assignment term 3 evolution by natural selection

Life Sciences Term 3

• 1: Evolution by Natural Selection
• Introduction

Evolution is a process of gradual change that takes place over many generations, during which species of animals, plants, or insects slowly change some of their physical characteristics.

Theories of human evolution are based on research and scientific evidence that support the concept of continual change.  Sources like geology, anatomy, embryology, genetics and physiology have been used as explanations for the theories.  Further lines of evidence are fossil records, modification of descent, Biogeography and genetics.

Lamarck and Darwin are two of many scientists that have formulated theories about evolution.  Lamarck’s theory has been rejected while Darwin’s theory of evolution through natural selection has been accepted.

Module overview

This module deals with Evolution by natural selection. The module starts with notes and important “tips” for learners. There is a detailed terminology list, followed by evidence of evolution, Lamarckism and Darwinism, punctuated equilibrium, artificial selection, speciation, mechanisms of reproductive isolation and evolution in present times.

Learning outcomes

By the end of this module, you will be able to:

• Teach the terminology associated with evolution
• Create a cross word puzzle on the computer
• Explain the following as evidence for evolution:
• Fossil records
• Biogeography
• Modification by descent
• Give a review of the contribution of each of the following to variation that exists amongst individuals of the same species:
• Crossing over
• Random arrangement of chromosones
• Random fertilisation
• Random mating
• Distinguish between continuous and discontinuous variation
• Describe and apply the evolutionary theories of Darwin and Lamarck
• Administer the gr.12 SBA task and assess the task correctly
• Explain what Punctuated Equilibrium is
• Explain what artificial selection is
• Able to classify questions according Bloom’s taxonomy
• Explain how speciation takes place through geographic isolation
• Give a brief outline of reproductive isolation mechanisms that help to keep species separate
• Describe and explain an example of natural selection and evolution in present times.

Study materials

Module structure

Unit 1: terminology and defining the concepts of evolution.

• View the link below for further information on this topic
• Complete activity 1.1 on pages 5 - 6 of the module guide
• Using the NEW Word document below, complete activity 1.2 on page 7 of the module guide. Save this Word document in the following format: Full name_Module 1. This document will be used for further activities in this module.

Activity 1.1: Word search activity o/s!!!

Unit 2: evidence of evolution and sources of variation.

• View the link below for further information on this topic.

Unit 3: Lamarckism and Darwinism

• Using the SAME Word document, complete activity 1.3 on page 12 of the module guide
• Access the forum tool below to discuss the following with your peers:
• How could Lamarck have re-worded his theory if he had all the knowledge available today?
• Using the SAME Word document, complete activities 1.4, 1.5 and 1.6 on pages 14 - 18 of the module guide. Should you elect to draw the diagrams / graphs manually, take a picture of your diagram and save the image file in the following format: Full name_Module1 1_Activity X.X
• Access the forum tool 1.6 below to discuss the following with your peers:
• At the rate humans are misusing the earth, the possibility to have a very different earth in 100 year's time is very strong. What impace will this have on the animal and plant species on earth?

Unit 4: Punctuated equilibrium

• For further information on this topic, view the link below
• Using the SAME Word document, complete activity 1.7 on pages 23 - 27 of the module guide
• Access the discussion tool below to reflect on the following with your peers:
• What other species can you think of where punctuated equilibrium has occurred? What role does the environment play in punctuated equilibrium?

Unit 5: Artificial selection

• For further information on this topic, click on the link below
• Using the SAME Word document, complete activity 1.8 on pages 29 - 31 of your module guide
• For your convenience, the weighting table has been included as a soft copy below. Ensure that this document is submitted with all other activities / documents at the end of this module.

Unit 6: Speciation

• Using the SAME Word document, complete activity 1.9 on pages 33 - 35 of the module guide
• Review activity 1.10 and reflect on how you can use this activity in your classroom.

Unit 7: Mechanisms of reproductive isolation

• Using the SAME Word document, complete activity 1.11 on pages 38 - 39 of the module guide.

Unit 8: Evolution in present times

• Click on the link below for further information on this topic
• Using the SAME Word document, complete activity 1.12 on pages 41 - 43 of the module guide
• Submit ALL your activity documents / image files by using the submission tool below.

Subject methodology

Enrichment resources.

Review the enrichment resources below. One of the videos by Origins Explained, runs through 10 alternative evolution theories. This video could open up some interesting discussions with your learners?

Technology support

The two links below entail online Evolution games which can be incorporated into your lesson plans on this topic. Are these resources which you'd be willing to investigate as teaching aids?

Module summary

Life exists in a variety of life forms and it is in the study of Evolution through Natural Selection that enables learners to understand where the biodiversity that exists today evolved from and how the millions of species came about.

• 2: Human evolution
• 3: Responding to the environment: Plants
• Additional resources: Past exam papers
• Additional resources: Lesson plans

Stay in touch

• http://mgslg.co.za/
• +27 (11) 830 0768 or +27 (11) 830 2201

Open Yale Courses

You are here, eeb 122: principles of evolution, ecology and behavior,  - adaptive evolution: natural selection.

Adaptive Evolution is driven by natural selection. Natural selection is not “survival of the fittest,” but rather “reproduction of the fittest.” Evolution can occur at many different speeds based on the strength of the selection driving it. These types of selection can result in directional, stabilizing, and disruptive outcomes. They can be driven by frequency-dependent selection and sexual selection, in addition to more standard types of selection.

You may view the Yale Galapagos site at:  http://cmi2.yale.edu/galapagos_public

Lecture Chapters

• Introduction
• Strength of Selection and the Speed of Evolution
• Why Evolution Can Be Slow
• Types of Selection
• Large Scale Selection

• Introduction to Ecology; Major patterns in Earth’s climate
• Behavioral Ecology
• Population Ecology 1
• Population Ecology 2
• Community Ecology 1
• Community Ecology 2
• Ecosystems 1
• Ecosystems 2
• Strong Inference
• What is life?
• What is evolution?

Evolution by Natural Selection

• Other Mechanisms of Evolution
• Population Genetics: the Hardy-Weinberg Principle
• Phylogenetic Trees
• Earth History and History of Life on Earth
• Origin of Life on Earth
• Gene expression: DNA to protein
• Gene regulation
• Cell division: mitosis and meiosis
• Mendelian Genetics
• Chromosome theory of inheritance
• Patterns of inheritance
• Chemical context for biology: origin of life and chemical evolution
• Biological molecules
• Membranes and Transport
• Energy and enzymes
• Respiration, chemiosmosis and oxidative phosphorylation
• Oxidative pathways: electrons from food to electron carriers
• Fermentation, mitochondria and regulation
• Why are plants green, and how did chlorophyll take over the world? (Converting light energy into chemical energy)
• Carbon fixation
• Recombinant DNA
• Cloning and Stem Cells
• Adaptive Immunity
• Human evolution and adaptation

Learning Objectives

• Define and recognize fitness , adaptation , and evolution by natural selection
• Explain predictions of and evidence for evolution by natural selection
• Identify, explain, and recognize the consequences of evolution by natural selection in terms of fitness, adaptation, average phenotype, and genetic diversity
• Differentiate between directional, stabilizing, disruptive, and balancing selection

A Short Primer on Genetics

Charles Darwin and Alfred Russel Wallace articulated the theory of evolution by natural selection without a modern understanding of genetics. But we have the advantage today of being able to discuss evolution with knowledge of genetics, so we’ll start with a brief primer on genetics. These basic genetic concepts are good to review to make sure we’re all on the same page:

• A ll living things have DNA as their genetic material. DNA is composed of nucleotide bases, commonly abbreviated as A, T, C, and G.
• DNA is organized into one or more chromosomes , which are linear or circular structures comprised of DNA and associated proteins
• An organism’s genome is the complete set of genes or genetic material for that species.
• A  gene  is a hereditary factor that determines (or influences) a particular trait.  A gene is comprised of a specific DNA sequence and is located on a specific region of a specific chromosome.  Because of its specific location, a gene can also be called a  genetic locus.
• An  allele  is a particular variant of a gene, in the same way that chocolate and vanilla are particular variants of ice cream.
• An organism’s  genotype  is the particular collection of alleles found in its DNA.  An organism with two of the same alleles for a particular gene is  homozygous  at that locus; an organism with two different alleles for a particular gene is  heterozygous  at that locus.
• An organism’s  phenotype is its observable traits, which can include physical features and behaviors. Some aspects of phenotype are influenced by genotype, and some are influenced by environment.
• A  mutation is a change in the DNA sequence (A, T, C, or G). Some mutations are deleterious (‘bad’), some have no effect (‘neutral’), and some are beneficial (‘good’).  Mutations create new alleles, so without mutations, there would be no new genetic variation.

Evolution by natural selection occurs when certain genotypes produce more offspring than other genotypes in response to the environment. It is a non-random change in allele frequencies from one generation to the next. In On the Origin of Species by Natural Selection (1859), Charles Darwin described four requirements for evolution by natural selection:

• the trait under selection must be variable in the population, so that the encoding gene has more than one variant, or allele.
• the trait under selection must be heritable , encoded by a gene or genes
• the struggle of existence , that many more offspring are born than can survive in the environment.
• individuals with different alleles have differential survival and reproduction that is governed by the fit of the organism to its environment

• The population initially contains only antibiotic-sensitive alleles (meaning the antibiotic will kill the cells), but mutations generate antibiotic resistant alleles. Now the trait under selection (antibiotic resistance) is variable in the population, with at least two alleles.
• The antibiotic-resistant individuals have offspring that are also resistant because they have the same gene mutation for resistance, indicating that the trait is heritable .
• Both sensitive and resistant bacteria have lots of offspring inside the infected human host (or on the petri dish) and compete for resources inside the host.
• Because the human host is taking a course of antibiotics (or the petri dish contains increasing dosages of antibiotic), bacteria with the sensitive alleles die more-so than bacteria with the resistant allele. The resistant bacteria are a better fit to the antibiotic-rich environment.

This brings us to the idea of Darwinian fitness , that the organisms that best match their environment will have relatively greater survival and reproduction than those that match less well. Fitness is quantified relative to the average individual in the population; individuals that produce more viable progeny (progeny that can live and reproduce themselves) than average have greater fitness. A trait that is heritable and increases the survival and reproduction odds for those that carry that trait is called an adaptation . If a trait confers 1% greater reproductive advantage, it confers a fitness of 1.01. A trait that confers 10% greater reproductive advantage has a fitness of 1.1. Of all the mechanisms of evolution we’ll discuss in this course, only natural selection results in adaptations. Remember, the measure of fitness is production of viable progeny – adaptive traits promote survival of individuals to reproductive age and/or promote reproductive success.

Evolution by natural selection results in individuals that are a better fit to their environment

Evolution by natural selection occurs when the environment exerts a pressure on a population so that only some phenotypes survive and reproduce successfully. The stronger the selective pressure or the selection event the fewer individuals make it through the sieve of natural selection. Those phenotypes that survive a strong selection event, such as a drought, are a better fit for an environment that suffers drought. Another way to say this is that they have higher Darwinian fitness .

The finches on the Galápagos islands have provided a robust study system for observing natural selection in action over the past decades (see the work of Peter and Rosemary Grant and their collaborators). The small finches on the island of Daphna Major have strong beaks to feed on seeds. Smaller beaked birds can only crack open the smallest seeds, while birds with larger beaks prefer larger seeds. In 1977, drought reduced the number of small seeds, so many small-beaked finches starved to death.

A drought on the Galápagos island of Daphne Major in 1977 reduced the number of small seeds available to finches, causing many of the small-beaked finches to die. This caused an increase in the finches’ average beak size between 1976 and 1978.

In the finch example above, the average phenotype has shifted so most individuals have larger beaks, which is a genetically controlled-trait in the finches. The larger beak size is an adaptation to the seed sizes available during drought conditions. A result of this shift is that small beak phenotypes have become rare or disappeared, so there is reduced phenotypic and therefore reduced genetic diversity in the finch population after selection. When a population displays a normal distribution for a particular trait, natural selection can drive change in populations in different directions depending on the type of selection.

Stabilizing selection results in a narrowing of the normal distribution, because individuals who had the ‘average’ phenotype, or the phenotype closest to the mean, tend to leave more offspring than those with phenotypes at either extreme. Directional selection results in a shift toward one end of the normal distribution, because individuals who had one extreme of the phenotype tend to leave more offspring than those with the other extreme. Disruptive or diversifying selection results in separation of the normal distribution into two distributions with elimination of the middle of the peak, because individuals with either extreme phenotype tend to have more offspring than those with the intermediate phenotype. Balancing selection occurs when multiple phenotypes (or alleles) are actively maintained in the population (i.e., no single phenotype has a consistent selective advantage over any other).  The two most common types of balancing selection are frequency-dependent selection, where fitness depends on how common the phenotype (or allele) is, and heterozygote advantage , where the heterozygote (with the combined phenotype of both alleles) has higher fitness than either homozygote.

The image below illustrates the different effects on a population due to stabilizing, directional, or disruptive (diversifying) selection:

Does evolution of bigger, sexually reproducing organisms happen on time scales faster than geologic time? 

Yes! There are lots of great examples of evolution, even in sexually reproducing species, that happen pretty quickly, on the order of years or decades. In fact, the relevant time unit is generations. Rock Pocket mice in the desert southwest are a long-studied example. These small tan mice are hunted by owls, visual predators who spot the mice by their contrasting color against the sand. Most mice are exactly the same color as the sand. This short video explains what happens to a pocket mice population that migrates onto black volcanic rock, with mutation rates and the number of generations until the population shifts from all tan to all black coat color.

Examples of how evolution matters to ordinary people

• The example of bacteria evolving resistance to antibiotics is just one example of how evolution affects people’s lives. Here are some questions for you to consider in the light of evolution:
• How is cancer an evolutionary disease? Cancer arises because individual cells acquire mutations that they pass on to their progeny via mitosis. These mutations allow these cells to escape growth inhibition and hog resources (by creating new blood vessels and ramping up metabolism).
• When we use insecticides in our homes, and farmers spray their fields, how will the targeted insect population evolve?
• When fishing regulations limit the catch to larger fish, what consequences might that have?

Additional optional readings

The Escape of the Pathogens: an evolutionary arms race

Antibiotic resistance: delaying the inevitable

UN Sustainable Development Goal (SDG) 3: Good Health and Well-being – Understanding the principles of evolution and natural selection can help us combat antibiotic resistance and develop effective medical treatments. Strong foundations in evolution can aid the development and proper application of vaccines and limit the spread of new and emerging infectious diseases.

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18.2: Understanding Evolution

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Learning Objectives

By the end of this section, you will be able to do the following:

• Describe how scientists developed the present-day theory of evolution
• Define adaptation
• Explain convergent and divergent evolution
• Describe homologous and vestigial structures
• Discuss misconceptions about the theory of evolution

Evolution by natural selection describes a mechanism for how species change over time. Scientists, philosophers, researchers, and others had made suggestions and debated this topic well before Darwin began to explore this idea. Classical Greek philosopher Plato emphasized in his writings that species were static and unchanging, yet there were also ancient Greeks who expressed evolutionary ideas. In the eighteenth century, naturalist Georges-Louis Leclerc Comte de Buffon reintroduced ideas about the evolution of animals and observed that various geographic regions have different plant and animal populations, even when the environments are similar. Some at this time also accepted that there were extinct species.

Also during the eighteenth century, James Hutton, a Scottish geologist and naturalist, proposed that geological change occurred gradually by accumulating small changes from processes operating like they are today over long periods of time. This contrasted with the predominant view that the planet's geology was a consequence of catastrophic events occurring during a relatively brief past. Nineteenth century geologist Charles Lyell popularized Hutton's view. A friend to Darwin. Lyell’s ideas were influential on Darwin’s thinking: Lyell’s notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for this change. In the early nineteenth century, Jean-Baptiste Lamarck published a book that detailed a mechanism for evolutionary change. We now refer to this mechanism as an inheritance of acquired characteristics by which the environment causes modifications in an individual, or offspring could use or disuse of a structure during its lifetime, and thus bring about change in a species. While many discredited this mechanism for evolutionary change, Lamarck’s ideas were an important influence on evolutionary thought.

Charles Darwin and Natural Selection

In the mid-nineteenth century, two naturalists, Charles Darwin and Alfred Russel Wallace, independently conceived and described the actual mechanism for evolution. Importantly, each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on H.M.S. Beagle , including stops in South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands west of Ecuador. On these islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape (Figure 18.2). The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the South American mainland. Darwin imagined that the island species might be species modified from one of the original mainland species. Upon further study, he realized that each finch's varied beaks helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.

Wallace and Darwin both observed similar patterns in other organisms and they independently developed the same explanation for how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection , or “survival of the fittest,” is the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits. This leads to evolutionary change.

For example, Darwin observed a population of giant tortoises in the Galápagos Archipelago to have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks. In times of drought when fewer leaves would be available, those that could reach more leaves had a better chance to eat and survive than those that couldn’t reach the food source. Consequently, long-necked tortoises would be more likely to be reproductively successful and pass the long-necked trait to their offspring. Over time, only long-necked tortoises would be present in the population.

Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, most characteristics of organisms are inherited, or passed from parent to offspring. Although no one, including Darwin and Wallace, knew how this happened at the time, it was a common understanding. Second, more offspring are produced than are able to survive, so resources for survival and reproduction are limited. The capacity for reproduction in all organisms outstrips the availability of resources to support their numbers. Thus, there is competition for those resources in each generation. Both Darwin and Wallace’s understanding of this principle came from reading economist Thomas Malthus' essay that explained this principle in relation to human populations. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Darwin and Wallace reasoned that offspring with inherited characteristics which allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment. It is the only mechanism known for adaptive evolution.

In 1858, Darwin and Wallace (Figure 18.3) presented papers at the Linnean Society in London that discussed the idea of natural selection. The following year Darwin’s book, On the Origin of Species, was published. His book outlined in considerable detail his arguments for evolution by natural selection.

It is difficult and time-consuming to document and present examples of evolution by natural selection. The Galápagos finches are an excellent example. Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important evidence of natural selection. The Grants found changes from one generation to the next in beak shape distribution with the medium ground finch on the Galápagos island of Daphne Major. The birds have inherited a variation in their bill shape with some having wide deep bills and others having thinner bills. During a period in which rainfall was higher than normal because of an El Niño, there was a lack of large hard seeds of which the large-billed birds ate; however, there was an abundance of the small soft seeds which the small-billed birds ate. Therefore, the small-billed birds were able to survive and reproduce. In the years following this El Niño, the Grants measured beak sizes in the population and found that the average bill size was smaller. Since bill size is an inherited trait, parents with smaller bills had more offspring and the bill evolved into a much smaller size. As conditions improved in 1987 and larger seeds became more available, the trend toward smaller average bill size ceased.

Career Connection

Field Biologist Many people hike, explore caves, scuba dive, or climb mountains for recreation. People often participate in these activities hoping to see wildlife. Experiencing the outdoors can be incredibly enjoyable and invigorating. What if your job entailed working in the wilderness? Field biologists by definition work outdoors in the “field.” The term field in this case refers to any location outdoors, even under water. A field biologist typically focuses research on a certain species, group of organisms, or a single habitat (Figure 18.4).

One objective of many field biologists includes discovering new, unrecorded species. Not only do such findings expand our understanding of the natural world, but they also lead to important innovations in fields such as medicine and agriculture. Plant and microbial species, in particular, can reveal new medicinal and nutritive knowledge. Other organisms can play key roles in ecosystems or if rare require protection. When discovered, researchers can use these important species as evidence for environmental regulations and laws.

Processes and Patterns of Evolution

Natural selection can only take place if there is variation , or differences, among individuals in a population. Importantly, these differences must have some genetic basis; otherwise, the selection will not lead to change in the next generation. This is critical because nongenetic reasons can cause variation among individuals such as an individual's height because of better nutrition rather than different genes.

Genetic diversity in a population comes from two main mechanisms: mutation and sexual reproduction. Mutation, a change in DNA, is the ultimate source of new alleles, or new genetic variation in any population. The genetic changes that mutation causes can have one of three outcomes on the phenotype. A mutation affects the organism's phenotype in a way that gives it reduced fitness—lower likelihood of survival or fewer offspring. A mutation may produce a phenotype with a beneficial effect on fitness. Many mutations will also have no effect on the phenotype's fitness. We call these neutral mutations. Mutations may also have a whole range of effect sizes on the organism's fitness that expresses them in their phenotype, from a small effect to a great effect. Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each offspring.

We call a heritable trait that helps an organism's survival and reproduction in its present environment an adaptation . Scientists describe groups of organisms adapting to their environment when a genetic variation occurs over time that increases or maintains the population's “fit” to its environment. A platypus's webbed feet are an adaptation for swimming. A snow leopard's thick fur is an adaptation for living in the cold. A cheetah's fast speed is an adaptation for catching prey.

Whether or not a trait is favorable depends on the current environmental conditions. The same traits are not always selected because environmental conditions can change. For example, consider a plant species that grew in a moist climate and did not need to conserve water. Large leaves were selected because they allowed the plant to obtain more energy from the sun. Large leaves require more water to maintain than small leaves, and the moist environment provided favorable conditions to support large leaves. After thousands of years, the climate changed, and the area no longer had excess water. The direction of natural selection shifted so that plants with small leaves were selected because those populations were able to conserve water to survive the new environmental conditions.

The evolution of species has resulted in enormous variation in form and function. Sometimes, evolution gives rise to groups of organisms that become tremendously different from each other. We call two species that evolve in diverse directions from a common point divergent evolution . We can see such divergent evolution in the forms of the reproductive organs of flowering plants which share the same basic anatomies; however, they can look very different as a result of selection in different physical environments and adaptation to different kinds of pollinators (Figure 18.5).

In other cases, similar phenotypes evolve independently in distantly related species. For example, flight has evolved in both bats and insects, and they both have structures we refer to as wings, which are adaptations to flight. However, bat and insect wings have evolved from very different original structures. We call this phenomenon convergent evolution , where similar traits evolve independently in species that do not share a recent common ancestry. The trait in the two species came to be similar in structure and have the same function, flying, but did so separately from each other.

These physical changes occur over enormous time spans and help explain how evolution occurs. Natural selection acts on individual organisms, which can then shape an entire species. Although natural selection may work in a single generation on an individual, it can take thousands or even millions of years for an entire species' genotype to evolve. It is over these large time spans that life on earth has changed and continues to change.

Evidence of Evolution

The evidence for evolution is compelling and extensive. Looking at every level of organization in living systems, biologists see the signature of past and present evolution. Darwin dedicated a large portion of his book, On the Origin of Species , to identifying patterns in nature that were consistent with evolution, and since Darwin, our understanding has become clearer and broader.

Fossils provide solid evidence that organisms from the past are not the same as those today, and fossils show the gradual evolutionary changes over time. Scientists determine the age of fossils and categorize them from all over the world to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years (Figure 18.6). For example, scientists have recovered highly detailed records showing the evolution of humans and horses (Figure 18.6). The whale flipper shares a similar morphology to bird and mammal appendages (Figure 18.7) indicating that these species share a common ancestor.

Anatomy and Embryology

Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For example, the bones in human, dog, bird, and whale appendages all share the same overall construction (Figure 18.7) resulting from their origin in a common ancestor's appendages. Over time, evolution led to changes in the bones' shapes and sizes in different species, but they have maintained the same overall layout. Scientists call these synonymous parts homologous structures .

Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past common ancestor. We call these unused structures without function vestigial structures . Other examples of vestigial structures are wings on flightless birds, leaves on some cacti, and hind leg bones in whales. Not all similarities represent homologous structures. As explained in Determining Evolutionary Relationships, when similar characteristics occur because of environmental constraints and not due to a close evolutionary relationship, it is an analogy or homoplasy. For example, insects use wings to fly like bats and birds, but the wing structure and embryonic origin are completely different. These are analogous structures (Figure 20.8).

Link to Learning

Watch this video exploring the bones in the human body.

Another piece of evidence of evolution is the convergence of form in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan, living in the arctic region have been selected for seasonal white phenotypes during winter to blend with the snow and ice (Figure 18.8). These similarities occur not because of common ancestry, but because of similar selection pressures—the benefits of predators not seeing them.

Embryology, the study of the anatomy of an organism's development to its adult form, also provides evidence of relatedness between now widely divergent groups of organisms. Mutational tweaking in the embryo can have such magnified consequences in the adult that tends to conserve embryo formation. As a result, structures that are absent in some groups often appear in their embryonic forms and disappear when they reach the adult or juvenile form. For example, all vertebrate embryos, including humans, exhibit gill slits and tails at some point in their early development. These disappear in the adults of terrestrial groups but adult forms of aquatic groups such as fish and some amphibians maintain them. Great ape embryos, including humans, have a tail structure during their development that they lose when they are born.

Biogeography

The geographic distribution of organisms on the planet follows patterns that we can explain best by evolution in conjunction with tectonic plate movement over geological time. Broad groups that evolved before the supercontinent Pangaea broke up (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America was most predominant prior to the southern supercontinent Gondwana breaking up.

Marsupial diversification in Australia and the absence of other mammals reflect Australia’s long isolation. Australia has an abundance of endemic species—species found nowhere else—which is typical of islands whose isolation by expanses of water prevents species to migrate. Over time, these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. Australia's marsupials, the Galápagos' finches, and many species on the Hawaiian Islands are all unique to their one point of origin, yet they display distant relationships to ancestral species on mainlands.

Molecular Biology

Like anatomical structures, the molecular structures of life reflect descent with modification. DNA's universality reflects evidence of a common ancestor for all of life. Fundamental divisions in life between the genetic code, DNA replication, and expression are reflected in major structural differences in otherwise conservative structures such as ribosome components and membrane structures. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences—exactly the pattern that we would expect from descent and diversification from a common ancestor.

DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events that allow freely modifying one copy by mutation, selection, or drift (changes in a population’s gene pool resulting from chance), while the second copy continues to produce a functional protein.

Misconceptions of Evolution

Although the theory of evolution generated some controversy when Darwin first proposed it, biologists almost universally accepted it, particularly younger biologists, within 20 years after publication of On the Origin of Species . Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound.

This site addresses some of the main misconceptions associated with the theory of evolution.

Evolution Is Just a Theory

Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word “theory” with the way scientists use the word. In science, we understand a “theory” to be a body of thoroughly tested and verified explanations for a set of observations of the natural world. Scientists have a theory of the atom, a theory of gravity, and the theory of relativity, each which describes understood facts about the world. In the same way, the theory of evolution describes facts about the living world. As such, a theory in science has survived significant efforts to discredit it by scientists. In contrast, a “theory” in common vernacular is a word meaning a guess or suggested explanation. This meaning is more akin to the scientific concept of “hypothesis.” When critics of evolution say it is “just a theory,” they are implying that there is little evidence supporting it and that it is still in the process of rigorous testing. This is a mischaracterization.

Individuals Evolve

Evolution is the change in a population's genetic composition over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. Individuals do change over their lifetime, obviously, but this is development and involves changes programmed by the set of genes the individual acquired at birth in coordination with the individual’s environment. When thinking about the evolution of a characteristic, it is probably best to think about the change of the average value of the characteristic in the population over time. For example, when natural selection leads to bill-size change in medium ground finches in the Galápagos, this does not mean that individual bills on the finches are changing. If one measures the average bill size among all individuals in the population at one time and then measures them in the population several years later, this average value will be different as a result of evolution. Although some individuals may survive from the first time to the second, they will still have the same bill size; however, there will be many new individuals who contribute to the shift in average bill size.

Evolution Explains the Origin of Life

It is a common misunderstanding that evolution includes an explanation of life’s origins. Some of the theory’s critics believe that it cannot explain the origin of life. The theory does not try to explain the origin of life. The theory of evolution explains how populations change over time and how life diversifies the origin of species. It does not shed light on the beginnings of life including the origins of the first cells, which define life. Importantly, biologists believe that the presence of life on Earth precludes the possibility that the events that led to life on Earth can repeat themselves because the intermediate stages would immediately become food for existing living things.

However, once a mechanism of inheritance was in place in the form of a molecule like DNA either within a cell or pre-cell, these entities would be subject to the principle of natural selection. More effective reproducers would increase in frequency at the expense of inefficient reproducers. While evolution does not explain the origin of life, it may have something to say about some of the processes operating once pre-living entities acquired certain properties.

Organisms Evolve on Purpose

Statements such as “organisms evolve in response to a change in an environment” are quite common, but such statements can lead to two types of misunderstandings. First, do not interpret the statement to mean that individual organisms evolve. The statement is shorthand for “a population evolves in response to a changing environment.” However, a second misunderstanding may arise by interpreting the statement to mean that the evolution is somehow intentional. A changed environment results in some individuals in the population, those with particular phenotypes, benefiting and therefore producing proportionately more offspring than other phenotypes. This results in change in the population if the characteristics are genetically determined.

It is also important to understand that the variation that natural selection works on is already in a population and does not arise in response to an environmental change. For example, applying antibiotics to a population of bacteria will, over time, select a population of bacteria that are resistant to antibiotics. The resistance, which a gene causes, did not arise by mutation because of applying the antibiotic. The gene for resistance was already present in the bacteria's gene pool, likely at a low frequency. The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects individuals that are resistant, since these would be the only ones that survived and divided. Experiments have demonstrated that mutations for antibiotic resistance do not arise as a result of antibiotic.

In a larger sense, evolution is not goal directed. Species do not become “better” over time. They simply track their changing environment with adaptations that maximize their reproduction in a particular environment at a particular time. Evolution has no goal of making faster, bigger, more complex, or even smarter species, despite the commonness of this kind of language in popular discourse. What characteristics evolve in a species are a function of the variation present and the environment, both of which are constantly changing in a nondirectional way. A trait that fits in one environment at one time may well be fatal at some point in the future. This holds equally well for insect and human species.

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Students explain evolution by natural selection differently for humans versus nonhuman animals

• Joelyn de Lima
• Tammy M. Long

W.K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060

Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland

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*Address correspondence to: Tammy M. Long ( E-mail Address: [email protected] ).

Department of Plant Biology, Michigan State University, East Lansing, MI 48824

Evolution is foundational to understanding biology, yet learners at all stages have incomplete and incorrect ideas that persist beyond graduation. Contextual features of prompts (e.g., taxon of organism, acquisition vs. loss of traits, etc.) have been shown to influence both the learning process and the ideas students express in explanations of evolutionary processes. In this study, we compare students’ explanations of natural selection for humans versus a nonhuman animal (cheetah) at different times during biology instruction. We found “taxon” to be a significant predictor of the content of students’ explanations. Responses to “cheetah” prompts contained a larger number and diversity of key concepts (e.g., variation, heritability, differential reproduction) and fewer naïve ideas (e.g., need, adapt) when compared with responses to an isomorphic prompt containing “human” as the organism. Overall, instruction increased the prevalence of key concepts, reduced naïve ideas, and caused a modest reduction in differences due to taxon. Our findings suggest that the students are reasoning differently about evolutionary processes in humans as compared with nonhuman animals, and that targeted instruction may both increase students’ facility with key concepts while reducing their susceptibility to contextual influences.

INTRODUCTION

Dobzhansky (1973) famously wrote, “Nothing in biology makes sense except in the light of evolution”. As such, evolutionary theory provides the needed context, underpinnings, and coherence to understand biological complexity ( Alters and Alters, 2001 ; Blackwell et al. , 2003 ). Evolution is to biology what plate tectonics is to geology, relativity is to time, and heliocentrism is to astronomy ( Deniz and Borgerding, 2018a ). However, despite its importance, it is perhaps one of the most controversial and polarizing science topics ( Glaze and Goldston, 2015 ; Pobiner, 2016 ). Across many countries and cultures, a significant proportion of people do not accept evolution as the unifying theory that explains the origin and diversity of life ( Downie and Barron, 2000 ; Miller et al. , 2006 ; Nehm and Schonfeld, 2007 ; Thagard and Findlay, 2010 ; Smith, 2010a , 2010b ; Allmon, 2011 ; Council of Europe, 2017 ; Oliveira and Cook, 2018 ; Deniz and Borgerding, 2018b ; Brenan, 2019 ).

Understanding evolution is a critical component of science literacy and its centrality to the biology curriculum is broadly valued by the scientific community. National and international reports that provide guidance for science teaching at both the K-12 and undergraduate level have stressed inclusion of evolution as a foundational concept ( AAAS, 2011 ; NGSS Lead States, 2013 ; UK Department of Education, 2015 ; Deniz and Borgerding, 2018a ). However, a significant number of students graduate from college without an understanding of evolution even after rigorous training in science ( Alters and Nelson, 2002 ; Kalinowski et al. , 2010 ; Pobiner et al. , 2018 ).

Students have great difficulty comprehending and explaining evolution, and misconceptions often persist despite explicit instruction ( Bishop and Anderson, 1990 ; Nehm and Reilly, 2007 ; Sinatra et al. , 2008 ; Bray Speth et al. , 2009 ; Catley and Novick, 2009 ; Morabito et al. , 2010 ; Smith, 2010a , 2010b ; Nehm and Ridgway, 2011 ). Some studies have suggested that students are also less likely to retain concepts related to evolution than noncontroversial topics such as photosynthesis ( Sinatra et al. , 2003 ; Nehm and Schonfeld, 2007 ; Glaze and Goldston, 2015 ). Developing conceptual understanding of evolutionary concepts is further inhibited by the presence of lexically ambiguous terms (e.g., pressure, purpose, cause, adapt; Mead and Scott, 2010a , 2010b ; Rector et al. , 2013 ).

Theoretical Framework and Research Questions

As with any concept, students’ knowledge and understanding of evolutionary theory is not created in a vacuum but is affected by the setting in which it is constructed ( Brown et al. , 1989 ; Hall, 1996 ; Van Oers, 1998 ). Context plays a vital role not only in shaping, but also in eliciting and activating this knowledge ( Jones et al. , 2000 ; Clark, 2006 ; Hofer, 2006 ; Sabella and Redish, 2007 ). These ideas are central to the theory of situated cognition which posits that learning and problem solving do not happen in abstraction, but rather by contextualizing and reasoning about information and problems using the particular context in which they are presented ( Brown et al. , 1989 ; Krish, 2009 ). According to this theory, knowledge is not directly transferred across contexts but is “ dynamically constructed, remembered, reinterpreted ” using contextual cues ( Clartcey, 2009 , p. 17). Therefore, understanding how context both helps and hinders learning and knowledge transfer is of paramount importance if we are to improve science literacy ( NASEM, 2016 , 2018 ).

As a construct, “context” can be complex because it can mean many things. For example, social and cultural contexts comprise multiple variables that characterize one’s physical space as well as associated norms, values, and behaviors. We are all likely familiar with the influence of one’s setting in how we approach and solve problems. For example, computing the same fraction may be perceived differently when baking a cake versus solving it as an item on a school math worksheet. Even experts are not immune from contextual influences. Gros et al. (2019) showed that experts struggled to solve simple math problems when contextualized around daily-life scenarios. Discipline imparts its own social and cultural context and has been shown to influence experts’ interpretations of relevant phenomena ( Schwarz et al. , 2020 ) and students’ reasoning and approaches to problem solving. For example, students coenrolled in college biology and chemistry courses used different language and reasoning when explaining both protein structure–function relationships ( Kohn et al. , 2018a ) and energy ( Kohn et al. , 2018b ) where differences were linked to the course in which they completed the assessment.

Given the potential for context to bias what knowledge is elicited, contextual features of prompts (i.e., prompt context) must be carefully considered when designing assessments. Prompt context can encompass a broad range of types and/or quantities of information included in a task stem, including personal perspectives, examples provided, activities of objects, amount of background text, etc. ( Son and Goldstone, 2009 ; Urhahne et al. , 2011 ; Krell et al. , 2012 ). Prompts that differ contextually despite testing for the same conceptual ideas have been shown to result in major differences in the content of students’ responses and performance on assessments ( Chi et al. , 1981 ; Potari and Spiliotopoulou, 1996 ; Schurmeier et al. , 2010 ). Even minor changes in phrasing can lead students to interpret a prompt differently than was intended or to focus on irrelevant or superficial features unrelated to the concept being assessed (e.g., diSessa et al. , 2004 ; Ozdemir and Clark, 2009 ). Often, such variations in task stems and assessment prompts create unintended differences between the items compared (e.g., the nature of examples provided results in differences in numbers of words or quantities of explanatory background) making it impossible to isolate the causal variable accounting for performance differences.

Assessing students’ conceptions of evolution, in particular, has proven especially sensitive to prompt context influences. Evans (2008) lists multiple studies that show major differences in responses to questions about micro- versus macroevolutionary processes. Kampourakis and Zogza (2008 , 2009 ) found the content of students’ responses related to differences in the structure and content of prompts that had been designed to be conceptually similar. However, among the many sources of variation in prompt context, organism (or biological taxon) emerges as a potential factor influencing students’ reasoning about evolution. An early study by Clough and Driver (1986) documented differences in the conceptual frameworks students applied when explaining evolution by natural selection for the origin and prevalence of different colors in caterpillars versus thick fur in Arctic foxes. Since then, numerous studies suggest organism may be a plausible/likely factor related to differences in students’ reasoning about and performance on evolution assessments (e.g., Ha et al. , 2006 ; Nehm and Schonfeld, 2008 ; Nehm and Ha, 2011 ; Göransson et al. , 2020 ).

Assessing evolutionary knowledge and understanding is most problematic when considering humans as the evolving organism. Ever since Darwin proposed evolutionary theory, human evolution by natural selection has been controversial. The society he lived in, including his peers (A.R. Wallace included), took objection to the fact that humans were not the exception ( Mayr, 1982 ). Even today, people are more willing to accept natural selection as an explanation for evolution of species other than humans ( Miller et al. , 2006 ; Nadelson and Southerland, 2012 ; Nadelson and Hardy, 2015 ). Such trends are seen even among college-educated adults ( Brenan, 2019 ). Many studies that have explored students’ acceptance of human evolution have shown that students reason differently in human versus nonhuman animal contexts ( Atran, 1998 ; Atran et al. , 2001 ; Nettle, 2010 ) and that acceptance of evolution increases when the organism in question is farther in evolutionary distance from humans ( Sinatra et al. , 2003 ; Evans, 2008 ).

While we know that evolution acceptance can be influenced when considering human versus nonhuman organisms ( Sbeglia and Nehm, 2019 ), we know less about whether differences extend to the content of students’ explanations about evolution by natural selection. Beggrow and Sbeglia (2019) showed that disciplinary context (anthropology vs. biology) was more important than prompt context (human vs. nonhuman) when explaining differences in student responses to questions about human and nonhuman evolution.

In this study, we aim to contribute to a growing understanding about the role of context in influencing students’ reasoning about evolution by asking: 1) How do contextual features influence the content of student responses to prompts about evolution by natural selection? In particular, we explore the influence of “humans” as a contextual feature in a prompt in comparison with nonhuman animals. Hereafter, and for the purposes of this study, we constrain our use of “context” to refer to a specific type of prompt context that explores item features of a prompt or task stem used in assessment (i.e., item-feature context). Our use of “context” is consistent with definitions offered by Krell et al. (2012 , 2015 ) and Nehm and Ha (2011) , where “context” refers to specific item features of an assessment prompt (e.g., the organism or trait that is the subject of the prompt) and influences of context are evaluated by comparing otherwise equivalent (i.e., isomorphic) prompts. And 2) How does a semester of active, learner-centered instruction influence the content of student responses to the same prompts? Evolution learning has long been known to be fraught with difficulty, including numerous misconceptions that are notoriously difficult to dislodge ( Bishop and Anderson, 1990 ; Nehm and Reilly, 2007 ; Sinatra et al. , 2008 ; Bray Speth et al. , 2009 ; Catley and Novick, 2009 ; Gregory, 2009 ; Morabito et al. , 2010 ; Smith, 2010a , 2010b ; Nehm and Ridgway, 2011 ). However, there is evidence that “active learning” approaches can be particularly effective in promoting more normative ideas about evolutionary processes ( Andrews et al. , 2011 ; Nehm et al. , 2022 ; Sbeglia and Nehm, 2022 ).

Setting, Participants, and Course Structure

This study was conducted at a large, public university in the Midwest in the United States with highest research activity ( The Carnegie Classification of Institutions of Higher Education, n.d. ). Data for these analyses came from student responses in a large introductory biology course for majors ( N = 194 students enrolled) that focused on content domains of genetics, evolution, and ecology. The course is targeted toward sophomores (59% of students in study) but also includes a significant number of juniors (31%) and few freshmen (3%) or seniors (7%). The course is the second in a two-course sequence required for life science majors; the first course focuses on cell and molecular biology. Of the enrolled students, 160 completed all required tasks and were included in the analysis. The study population was 61% female, 21% first-generation college students, and 21% non-White, with an average GPA of 3.2 (4.0 scale). In 2008–2009, the course was transformed to be active, collaborative, learner-centered, and focused on science practices, such as modeling, arguing from evidence, and analyzing and interpreting data. It is important to note, however, that the course was not designed nor modified in any way for the purposes of testing hypotheses related to this study.

Classes met twice weekly for 80-min per class meeting. A survey administered through CATME.org was used at the start of the semester to organize students into teams of four. Grouping criteria privileged diversity in students’ self-reported skills and leadership preferences, and homogeneity in their study habits and schedules. Instruction emphasized engaging students in practices, such as representing and interpreting data, reasoning from evidence, explaining phenomena through explanations and model-based assessments, and modeling biological processes and systems. Course-level learning goals were communicated in the syllabus and daily learning objectives were shared and discussed at the beginning of each class meeting.

Overall, the course was organized into three modules corresponding to primary content (genetics, evolution, and ecology) and linked by the theme of “biological variation”. For each module, overarching questions framed the content relative to the course theme and progressed as follows: 1) How does biological variation arise? How is it expressed and passed on to future generations of cells or organisms? 2) Why is biological variation important within a species? Why do populations differ over time and space? and 3) How does biological variation interact with the environment? Throughout, considerable emphasis was placed on connecting concepts learned in previous class periods to new content. For example, using one’s understanding of genes and alleles (from the genetics module) to explain natural selection (in the evolution module). In addition, case studies were used to explicitly link content across modules and emphasize a “common storyline” that cohered content (e.g., the genetics of the melanin system in dogs was linked to the evolution of dogs from wolves and to the ecology of wolves on Isle Royale).

Typical class periods consisted of short (5–20 min) bouts of instruction followed by questions or problem sets during which students worked in teams to test their ability to apply concepts, link new ideas to existing knowledge, and explore connections among related concepts and principles. In-class activities and homework were designed as low-stakes opportunities for practice and feedback and intentionally aligned with higher-stakes assessments (i.e., exams and quizzes) that aimed to test students’ ability to transfer their knowledge and skills. All assessments were designed using diverse cases and biological contexts to illuminate the transferability and foundational nature of core principles (e.g., central dogma, natural selection, matter transformation, etc.). This strategy was regularly and transparently communicated to students and students were frequently asked to model, explain, and compare instances of the same biological phenomenon across multiple cases (e.g., constructing models of evolution of antibiotic resistance in bacteria and comparing them directly to their models of evolution of fur color in mice). In this way, we aimed to promote students’ abilities to consistently elicit coherent mental models that linked canonical understandings of biological concepts and processes despite case-specific contextual variability.

Assessment Design

We designed four isomorphic prompts based on the ACORNS instrument ( Nehm et al. , 2012 ) to assess students’ explanations about natural selection in human and nonhuman animals. Prompts were designed as open-ended questions because prior research has shown they provide better insights into students’ thought processes and subject knowledge ( Foddy, 1993 ).

Each prompt contained the following basal structure: “ (Taxon) has (trait). How would biologists explain how a (taxon) with (trait) evolved from an ancestral (taxon) without (trait)? ” Contextual features of prompts varied in taxon (human vs. cheetah) and type of trait (structural vs. functional). Cheetahs were chosen as the organism to contrast with humans for several reasons. Cheetahs are broadly recognizable, and therefore a familiar context for students. In evolutionary terms, humans and cheetahs are not very distant (diverged approximately 96 MYA [ Kumar et al. , 2017 ] ), and therefore less likely to trigger perceptions about differences attributed to more distantly related species (e.g., snails or salamanders). In addition, prior studies have examined how students reason when the taxon is “cheetah” ( Bishop and Anderson, 1990 ; Nehm and Reilly, 2007 ; Nehm and Ha, 2011 ; Göransson et al. , 2020 ) so our prompt aligns well with prior studies that have examined students’ explanations of natural selection using the same context. “Structural traits” in this study refer to morphological traits that affect fitness, specifically “heel bones” in humans and “leg bones” in cheetahs. “Functional traits” are behavioral traits or abilities that similarly affect fitness, such as “walking upright” in humans and “running fast” in cheetahs. Because trait gain and trait loss have been shown to elicit different reasoning in students ( Nehm and Ha, 2011 ), we explicitly designed our prompts to only address trait gain.

From the four prompts, we created two forms of the assessment, hereafter “Human/Cheetah Assessment” (or, HCA, Figure 1A ). Each form contained two prompts that differed in taxon (one prompt with humans; one with cheetah) but only one trait type. In other words, forms controlled for trait type while testing for effects due to taxon. Form 1 assessed students’ reasoning about humans versus cheetahs with respect to structural traits, while Form 2 assessed reasoning about humans versus cheetahs for functional traits ( Figure 1A ). Each student therefore responded to prompts about both taxa (i.e., cheetah and human), but only one trait type (i.e., either structural traits or functional traits; not both; Figure 1B ). This design allowed us to fully distinguish differences in reasoning owing to organismal context from differences due to trait type.

FIGURE 1. Prompts used in the HCA . (A) Two forms of an assessment were developed that differed in trait type (structural vs. functional). (B) Each form prompted students ( n = 91, Form 1; n = 69, Form 2) to explain evolution by natural selection for both human and nonhuman animals. Students responded to the same form at the beginning and at the end of the semester.

To control for potential influences of order ( Schuman and Presser, 1996 ; Federer et al. , 2015 ), each form of the HCA was further divided into subforms that differed in the order of appearance of each taxon (i.e., half of the copies of each form had cheetah first and half had human first). Prior research has shown that student performance on assessment tasks can be affected by the sequence in which the assessment items are presented ( Monk and Stallings, 1970 ; Hambleton and Traub, 1974 ; Gray, 2004 ; Federer et al. , 2015 ; Carter and Prevost, 2018 ), and general recommendations are to take task order into consideration when designing assessments ( Schuman and Presser, 1996 ).

Students completed the HCA individually during class time for credit. Formative assessments were administered regularly in class and awarded credit for participation/effort. A study using the same ACORNS instrument, explored the effect of providing credit (extra credit vs. regular credit), and showed no differences in the patterns in student responses ( Sbeglia and Nehm, 2022 ).

In our study, each student provided responses to the same form of the HCA at the beginning and end of the semester (i.e., form was held constant, Figure 1B ). Only students who completed the HCA at both times were included in analyses ( N of students = 160). The two taxa (human and cheetah) were not referenced during instruction or assessment at any point in the course.

Coding Responses

Students’ explanations were coded using the online assessment tool EvoGrader ( Moharreri et al. , 2014 ). EvoGrader codes for the presence of six key evolution concepts (KCs; Variation, Heritability, Competition, Limited Resources, Differential Survival, and Nonadaptive) and three naïve ideas (NIs; Adapt, Need, and Use/Disuse; Table 1 ). EvoGrader’s reliability and validity have been established in previous studies (see Moharreri et al. , 2014 ) and demonstrated comparable to that of trained human raters (>0.81 Kappa) despite requiring 99% less time for scoring. It is important to note that EvoGrader evaluates presence/absence of concepts; additional analyses and coding approaches are necessary in order to make inferences about correct applications of concepts.

Modified from Moharreri et al. (2014) .

Data Analysis

Abundance and diversity of KCs and NIs . In ecology, abundance indices measure the relative frequencies of organisms in a community, while diversity indices (e.g., Shannon, Simpson) measure variation in the types of organisms (e.g., species) across different communities. In our analyses, we considered the sum of all students’ responses as analogous to a community, and subsets of them representing discrete populations (e.g., the population of responses to a cheetah prompt pre-instruction). We then explored both the diversity (KCs and NIs) and relative abundances of ideas (number of times each KC or NI appears) in the respective populations and in the community in general.

Regression analyses for total number of KCs and NIs . We fitted regressions to understand variation in the total number of KCs and NIs. Because the data (the number of KCs [or NIs] in a response) is discrete, we used a mixed-effects Poisson regression. Specifically, we modeled variation in the number of KCs (and NIs, as part of a separate model) as a function of five predictors of interest (prompt order, taxa, trait, task order, and pre/post) as well as one random intercept term (student ID). The random intercept term allows us to account for nonindependence in the data caused by having multiple measurements from the same student. The nonindependence is because responses from the same student are more similar on average than any two randomly selected responses.

We calculated the 95% confidence intervals on all parameter estimates based on the model standard errors (SEs). The models showed signs of underdispersion, so we refit the models to account for this in two different ways: 1) using a mixed-effects zero-inflated Poisson regression, and 2) using a mixed-effects Conway Maxwell Poisson regression. In both cases, the estimated coefficient values and p values were almost identical, indicating that dispersion was not a major problem. Therefore, we present the results from the mixed-effects Poisson here:

KC only: These responses had only key concepts. The maximum number of key concepts measurable by EvoGrader is six.

Mixed: These responses had both key concepts as well as naïve ideas.

NI only: These responses had only naïve ideas. The maximum number of naïve ideas measurable by EvoGrader is three.

None: These responses had no key concepts or naïve ideas.

The four groups are: KC only, Mixed (both KCs and NIs present), NI only and None (neither KCs nor NIs present).

For every pair of groups, we modeled the probability of a response belonging to each group as a function of five predictors of interest (prompt order, taxa, trait, task order, and pre/post) as well as one random intercept term (student ID). This approach of fitting several logistic regression models for all pairs of groups is equivalent to fitting one multinomial logistic regression predicting the probability of belonging to any of the four groups. We did not use the (conceptually simpler) multinomial approach in this case because of numerical instabilities producing unreliable output.

All statistical analyses were done using the R statistical environment v 3.6.3 ( R Core Team, 2020 ). We made use of the dplyr ( Wickham et al. , 2020 ) and tidyr ( Wickham and Henry, 2020 ) packages for data processing, lme4 ( Bates et al. , 2015 ) for mixed-effects logistic regressions, effects ( Fox, 2003 ) for computing and plotting marginal effects, DHARMa ( Hartig, 2018 ) to checking residuals of mixed-effects models for patterns of overdispersion and underdispersion and glmmTMB ( Brooks et al. , 2017 ) to fit mixed-effects Poisson regression.

Our results showed that students’ responses were influenced by both prompt context and instruction. Results of our specific analyses are presented with respect to each of our original research questions.

1) How do contextual features influence the content of student responses to prompts about evolution by natural selection?

Results of all three analytic approaches indicated that students’ responses ( N = 640 responses) were significantly influenced by both taxon and trait.

Both before and after instruction, responses to questions about cheetahs had more KCs and fewer NIs than questions about humans (with the exception of Variation). Figure 2 shows the percentage of responses that contained each of the six KCs and three NIs for each taxon. Limited Resources was the KC most sensitive to the effect of taxon both before and after instruction. Pre-instruction, only 24% ( n = 38) of responses to the human prompt mentioned Limited Resources compared with 62% ( n = 99) of responses to cheetah. This was virtually unchanged with instruction, with 29% ( n = 46) and 63% ( n = 101) of responses to human and cheetah, respectively, mentioning Limited Resources. In contrast, Variation increased significantly with instruction, but there was almost no difference due to taxon. Interestingly, post-instruction Variation is the only instance in which we saw a higher frequency of a KC in the human prompt (approximately 6% n = 10 more) compared with cheetah.

FIGURE 2. Percentage of responses that contain each of the six key concepts and three naïve ideas pre- and post-instruction. KCs occurred more frequently in cheetah responses and responses written at the end of the semester. NIs occurred less frequently at the end of the semester. For numeric data equivalents refer to Supplemental Table S1.

The mixed-effects Poisson regression (Supplemental Figures S1 and S2) and the mixed-effects logistic regression (Supplemental Figures S3–S8) both show that taxa and trait influence the content of student explanations. Two of the other predictors of interest (prompt order, task order) did not show any effects. The results relating to the final predictor of interest (instruction, i.e., pre/post) are described in the next section.

Overall, responses had an average of 1.7 KCs and 0.4 NIs. Number of KCs differed between taxa, with a mean of 1.8 KCs for cheetah versus 1.4 KCs for human ( p < 0.001; Figure 3 ). Most of the responses did not have any NIs, and the number of NIs differed based on the type of trait. Responses had an average of 0.3 NIs when the prompt was about a functional trait and 0.2 NIs when the prompt was about a structural trait ( p < 0.05; Figure 4 ).

FIGURE 3. Average number of KCs in responses for each of the two taxa, estimated by the fitted model.

FIGURE 4. Average number of NIs in responses for each of the two traits, estimated by the fitted model.

Students’ responses were even less likely to have either KCs only or a mixture of KCs and NIs, than no KCs or no ideas (KCs nor NIs) in their responses to the human prompt (relative to the cheetah prompt, p < 0.001, Table 3 ).

Values with asterisks are statistically significant (*** p < 0.001; ** p < 0.01; * p < 0.05).

Lower- and upper-confidence intervals are provided in the brackets. This table provides the coefficients for “Taxon” and “Trait”, however the model also included “Pre/post-instruction” as a predictor.

50% less likely to include a mixture of KCs and NIs in their responses, as opposed to only NIs or no ideas at all (Supplemental Figures S4 and S6)

6% less likely to include only KCs than only NIs (Supplemental Figure S7)

10% less likely to include only KCs than no ideas (Supplemental Figure S5).

Students’ responses were more likely to have only KCs, than a mixture of KCs and NIs when they were responding to prompts about a structural trait (relative to a functional trait, p < 0.01, Table 3 ). Students included only KCs ∼15% more frequently than they included a mixture of KCs and NIs when writing about structural traits (Supplemental Figure S8).

2) How does a semester of active, learner-centered instruction influence the content of student responses to the same prompts?

Results of the abundance and diversity of KCs and NIs in students’ responses (pre- and post-instruction) are shown in Figure 5, A and B , respectively ( N = 640 responses for both). Although six KCs are possible, we observed no more than four within any response ( n = 47) and a majority contained at least two ( n = 398). No KCs were present in 96 student responses. For NIs, the maximum of three naïve ideas were present in only a single response and a majority had 0 naïve ideas ( n = 466).

FIGURE 5. Frequencies of (A) KCs and (B) NIs in student responses pre- and post-instruction.

Overall, our results show that instruction increases the number of KCs in responses and decreases the number of responses containing no KCs. Similarly, instruction decreases the number of NIs per response and increases the frequency of responses with no NIs.

Differential Survival was the most frequently applied KC; it was present in more than 50% ( n = 167) of the responses pre-instruction and more than 63% ( n = 207) responses post, irrespective of prompt context. The least used KC was Non-Adaptive, which appeared in only 1.5% ( n = 5) of the responses post-instruction ( Figure 2 ). Variation was the KC most responsive to instruction, with 33% ( n = 105) and 47% ( n = 150) responses including its pre- and post-instruction, respectively. Post-instruction, >93% ( n = 140) of the responses that mentioned Variation were in the KC Only group; only 6.6% ( n = 10) of those responses had any NIs at the end of the semester, compared with 14% ( n = 15) at the beginning of the semester ( Figure 2 ). Taxon-specific differences in KCs decreased moderately with instruction, with the greatest reductions observed for Heritability (4.4%) and Limited Resources (3.7%; Figure 2 ).

The above trends are further corroborated by regression analyses ( Figure 6, A and B ) that show the results of our mixed effects Poisson regressions for significant fixed effects (pre/post-instruction) for KCs and NIs, respectively. Table 4 gives the odds ratios of multiple logistic regressions that show the relative odds of belonging to one of the four previously mentioned groups ( Table 2 ) based on pre/post-instruction (post-instruction as the reference value).

FIGURE 6. Average number of (A) KCs and (B) NIs in responses for pre- and post-instruction, estimated by the fitted model.

Values with asterisks are statistically significant (*** p < 0.001; ** p < 0.01; * p < 0.05, λ p < 0.1).

Lower- and Upper-Confidence intervals are provided in the brackets.

This table provides the coefficients for “Pre/post-instruction”, however the model also included ”Taxon” and “Trait” as predictors.

Overall, students’ responses contained more KCs following instruction, regardless of taxon or trait type. Post-instruction had 30% more KCs compared with pre-instruction (1.9 vs. 1.4, respectively; p ≤ 0.001; Figure 6A ). Additionally, responses had 40% fewer NIs at the end of the semester ( p ≤ 0.001; Figure 6B ).

Students’ responses were even more likely to have KCs only, than a mixture of KCs and NIs, or only NIs, or no ideas (KCs nor NIs) in their responses pre-instruction (relative to pre-instruction, p ranging from <0.001 to <0.05; Table 4 ).

13% more likely to include only KCs in their responses in their responses, as opposed to a mixture of KCs and NIs (Supplemental Figure S8)

3% more likely to include only KCs than only NIs (Supplemental Figure S7)

3% more likely to include only KCs than no ideas (Supplemental Figure S5).

Similar patterns were seen even when the responses were separated by taxa ( Figure 7, A and B ). Postinstruction, the number of responses that included only KCs increased and most of the students’ responses included only KCs. Additionally, the number of responses that included a mixture of KCs and NIs, only NIs, and no ideas, decreased at the end of the semester.

FIGURE 7. Changes in the contents of the responses for students’ responses to the (A) cheetah prompt and (B) human prompt. A total of 160 students provided four responses each: one to the cheetah prompt and one to the human prompt at the start of the semester (pre), and the same at the end of the semester (post). Plots created using SankeyMATIC.

Our results are consistent with predictions that emerge from theories of situated cognition—students’ explanations about evolution by natural selection were influenced by both contextual features of prompts (taxon and trait type) and by instruction. Here, we explore our findings in view of previous studies and offer some possible explanations for the patterns we see. Additionally, we will discuss implications for instruction and assessment.

Contextual effects of the prompt

The isomorphic prompts in our study share a common underlying structure and are intended to assess equivalent knowledge despite minor variations in an item feature unrelated to the construct of interest. Because they share the same prompt stem (except for the specific item feature that was intentionally varied) they are designed to go beyond defined standards of equivalency in difficulty and complexity ( Kjolsing and Van Den Einde, 2016 ) to test for students’ ability to transfer concepts across contexts. Terms such as “explanatory coherence” ( Kampourakis and Zogza, 2009 ), “knowledge coherence” ( Nehm and Ha, 2011 ), and “causal flexibility” ( Evans, 2008 ) refer to one’s ability to produce similar responses to isomorphic prompts and identify a relevant concept despite irrelevant or peripheral details. For example, Weston et al. (2015) , found that changing a species on questions about photosynthesis did not influence students’ responses. They state that students did not consider the species in the prompt to be a relevant detail and therefore, did not consider it when formulating their response. In contrast, many studies, including our own, have shown that students’ explanations about evolution by natural selection are highly susceptible to contextual features of question prompts ( Kampourakis and Zogza, 2008 ; Schurmeier et al. , 2010 ; Prevost et al. , 2013 ). In particular, our findings are consistent with others that suggest taxon may be particularly influential in shaping students’ responses ( Nehm and Ha, 2011 ; Beggrow and Sbeglia, 2019 ; Göransson et al. , 2020 ).

In each of our analyses, we found that “taxon” was the most important variable influencing the number and type of KCs in a response and the group to which the response belonged. Responses to prompts about human evolution had fewer KCs and were more likely to have NIs despite instruction. This suggests that students are reasoning differently about humans compared with nonhuman animals. Beggrow and Sbeglia (2019) found that even students who study humans as a focal organism (e.g., anthropology majors) responded with fewer KCs and more NIs in responses to questions about evolution in humans as compared with nonhuman animals. Similar results were obtained by Ha et al. (2006) who found that students were less likely to use “natural selection after mutation” as an explanation in response to questions about human evolution as compared with questions about plants and other animals. It is possible that because students consider humans taxonomically unique ( Coley, 2007 ) and not part of the evolutionary tree ( Coley and Tanner, 2015 ; AAAS, 2018 ) that they are willing to reason differently about humans in evolution contexts.

Effects of instruction

Increased use of KCs and decreased sensitivity to prompt contexts can be important indicators of students’ understanding of evolution and acceptable measures of instructional efficacy. Our results show that patterns of KCs and NIs changed following instruction. Specifically, we observed an increase in the number of KCs and decrease in the number of NIs per response, as well as a modest reduction in response differences due to taxon. There is abundant literature documenting the difficulties of evolution learning and its resistance to instruction ( Bishop and Anderson, 1990 ; Nehm and Reilly, 2007 ; Sinatra et al. , 2008 ; Bray Speth et al. , 2009 ; Catley and Novick, 2009 ; Morabito et al. , 2010 ; Smith, 2010a , 2010b ; Nehm and Ridgway, 2011 ). However, active learning approaches have been shown promising in improving student outcomes. In the specific context of evolution instruction, active learning appears to be effective in producing improved conceptual knowledge as measured by performance on ACORNS instruments. For example, ACORNS assessments were used to document positive learning gains: in introductory biology where differing intensities of active learning were paired with misconception-focused instruction ( Nehm et al. , 2022 ) and in an intensive practice-based professional development program for teachers ( Cofré et al. , 2017 ). At the undergraduate level, Andrews et al. (2011) showed that practices such as purposefully eliciting and challenging naïve conceptions and emphasizing conceptual frameworks were effective in improving students’ understanding of natural selection.

In our study, we are unable to speculate about causal mechanisms that could explain our outcomes because we did not manipulate nor quantify either our “active learning” approach nor any of the specific pedagogical practices comprised within it. However, we note that our pedagogy did include opportunities for students to explicitly confront misconceptions and apply conceptual frameworks (e.g., central dogma, natural selection, etc.) across diverse cases during in-class, collaborative activities and on homeworks and exams. Overall, our findings are consistent with research that shows that although instruction can increase the accuracy of students’ explanations of evolution ( Halldén, 1988 ; Nehm and Reilly, 2007 ; Bray Speth et al. , 2009 , 2014 ; Andrews et al. , 2011 ; Pobiner et al. , 2018 ; Nehm et al. , 2022 ), influences of context often persist ( Ha et al. , 2015 ; Aptyka et al. , 2022 ).

Of the KCs assessed, Variation was most responsive to instruction. Students’ use of Variation increased by 10.6% and 17.5% in cheetah and human contexts, respectively. In the course that was the target of this study, variation was a central theme. Course content was organized around the central questions of: 1) how does biological variation originate at the molecular level? 2) How is molecular-level variation expressed at the organismal level? And, 3) what are the consequences of organismal variation for evolution of populations and ecosystem function? Our data revealed that students gained an appreciation of variation during the semester (14% more inclusion of Variation on average in the post-semester responses). Our findings are consistent with those of Bray Speth et al. (2014) that observed improvement in students’ representations of origin of variation using a similar instructional approach. Additionally, in our study, variation was elicited to a greater extent by the human prompt post-instruction. This could be an artifact of student’s general tendency to categorize by species (not recognize individual-level variation) when asked about nonhuman animals as compared with humans ( Nettle, 2010 ), rather than a direct consequence of instruction causing them to appreciate Variation differentially between the species.

An appreciation of the causes, consequences, and extent of Variation is central to understanding evolution ( Halldén, 1988 ; Shtulman, 2006 ; Gregory, 2009 ; Emmons and Kelemen, 2015 ). Darwin himself recognized the importance of Variation ( Darwin, 1868 , p. 192) and lamented the lack of understanding of its origin ( Darwin, 1859 , p. 167). In our study, few of the responses that included Variation had any naïve ideas (9.8% of n = 255 responses across all taxa and at both time points). This is consistent with the findings of Shtulman and Schulz (2008) , who showed that students who have a better understanding of within-species variation also have an accurate and mechanistic understanding of natural selection.

We observed that although the presence of naïve ideas decreased post-instruction, they still persisted in students’ responses. At the start of the semester, 34% of responses had naïve ideas compared with the 20% of responses at the end of the semester. Our results are consistent with many studies that have shown that naïve ideas, a form of intuitive thinking, are remarkably resistant to change and frequently coexist with correct scientific conceptions that are fundamentally mutually exclusive ( Bishop and Anderson, 1990 ; Nehm and Reilly, 2007 ; Sinatra et al. , 2008 ; Bray Speth et al. , 2009 ; Smith, 2010a , 2010b ; Nehm and Ridgway, 2011 ; Shtulman and Valcarcel, 2012 ).

Linking findings with existing theory

Literature offers several insights that could account for the difficulties associated with teaching and learning evolution. Here, we discuss three hypotheses that may inform our understanding of the patterns we observed: worldview and intuitive thinking, prior knowledge and experience, and scientific expertise.

Students’ worldview and intuitive thinking.

A worldview is a set of deeply entrenched beliefs and expectations that form the framework of a person’s individuality and define how they see the world around them ( Glaze and Goldston, 2015 ). A worldview that is composed of seemingly coherent ideas can also have inconsistencies ( Gabora, 1998 ). These inconsistencies occur as a result of trying to generalize or create an abstraction based on new ideas and concepts, some of which fit into the existing worldview, and some of which need to be “stretched”. There are multiple theories that explain what happens when these new ideas conflict with or threaten an existing worldview ( Proulx et al. , 2012 ). One potential strategy is preventing the idea from being assimilated into the worldview and thereby holding conflicting views simultaneously ( Gabora, 1998 ; Taber et al. , 2011 ).

Worldviews regarding evolution often do not change after instruction ( Blackwell et al. , 2003 ; Cavallo and McCall, 2008 ) and can hinder understanding and acceptance of evolutionary theory ( Alters and Nelson, 2002 ; Nehm, 2006 ; Evans, 2008 ). Smith (2010a) proposes that such barriers due to worldview can be overcome through education and exposure to empirical evidence. Ingram and Nelson (2006) showed that after instruction about evolution students’ positive views toward evolution increased and students who showed the greatest gains were those who were initially undecided about evolution. Dunk et al (2019) argue that instruction about the nature of science and consideration of students’ social and religious identities can help to increase not only evolutionary knowledge but also acceptance. Cofré et al. , (2018) showed that evolution education that included explicit instruction on the nature of science increased acceptance of evolution. Regardless of the specific mechanism, inconsistencies between students’ worldviews and tenets of evolutionary theory (especially with respect to human evolution) could make students more susceptible to contextual influences.

Intuitive ways of thinking can also pose barriers to evolutionary understanding by promoting contextual susceptibility. Smith (2010b) describes these predictable ways of thinking as “rules of thumb” or default approaches that are ingrained into the brain. If one’s intuitions have proven useful in some contexts or gone unquestioned, they are more likely to be used in new situations where there is a general lack of knowledge. Researchers have documented such expected patterns when students reason about biological entities, processes, and phenomena ( Inagaki and Hatano, 2006 ; Coley and Tanner, 2015 ). Coley and Tanner (2015) categorized biological-intuitive thinking into three different types that they called “construals” namely: teleological thinking, essentialist thinking, and anthropocentric thinking. These patterns of reasoning are powerful and can pose incredible barriers to learning because students do not understand that their reasoning itself is erroneous ( Sinatra et al. , 2008 ). Among the most prevalent of these intuitive patterns is teleology, which is attributing a purpose to all events and their cause to intentional agency ( Coley and Tanner, 2015 ). For example, it is common in human discourse to explain an unexpected observation, phenomenon, or pattern by simply stating, “there must be a reason for it.” Such intuitive thinking that everything must have a “reason” or was guided by an overarching force aligns with naïve ideas like need and adapt, where new variation is perceived to arise within a species because it is needed and perpetuates notions that all members of a species are the same. The tendency to consider members of a species as “all the same” can deter students from appreciating the variation that is necessary for evolutionary change.

Students’ prior evolutionary knowledge and education.

Students arrive at every course with previous knowledge and prior conceptions about evolution that they have gained through their formal education and lived experiences. This knowledge often includes evolutionary misconceptions which have been well-documented in the literature (e.g., Gregory, 2009 ; West et al. , 2011 ). Alters and Nelson (2002) , listed several factors such as inconsistent language usage and contradictory learning that can contribute to misconceptions. For example, colloquial terms such as “fitness” and “adaptation” that have distinct meanings in and out of evolution contexts or seeing humans and dinosaurs coexisting in various media.

By the time students reach the undergraduate classroom, their knowledge about evolution has also been influenced by their formal education, the quantity and quality of which is not consistent. Although evolution is now a part of the required curriculum in many countries, it is not required in some and banned outright in others. Even in countries that require evolution to be taught, the grades at which it is introduced, the perspective from which it is taught, and the focus of evolution education varies widely ( Deniz and Borgerding, 2018b ). In the United States, 20 states have adopted the Next Generation Science Standards (NGSS), which are generally more comprehensive than other state standards with respect to evolution ( Gross et al. , 2013 ). However, in their review of the NGSS, Gross et al. (2013) stated that while these standards were better than many state standards with respect to evolution, they too had some important weaknesses including the way they dealt with heredity and the links between DNA and evolutionary relationships. In terms of our study, the major drawback we noticed with the NGSS is that they do not even mention human evolution.

Among the states that have not adopted the NGSS, some do not even mention the word “evolution” in their standards and others make superficial references to it ( Lerner, 2000 ; Vazquez, 2017 ). Additionally, adopting standards for evolution education does not guarantee they are actually being implemented ( Glaze and Goldston, 2015 ) or that they are being implemented consistently. In some cases, students continue to be taught alternative theories in addition to, or at times instead of evolution ( Bowman, 2008 ). Multiple studies have documented troublesome issues with teachers responsible for evolution education, ranging from inadequate preparation for teaching evolution ( Smith, 2010b ) to de-emphasizing or avoiding teaching it ( Glaze and Goldston, 2015 ) to purposefully teaching students that “evolution is wrong” ( BouJaoude et al. , 2011 ). Such variability and inconsistency in students’ instruction about evolution make it difficult to make any sort of assumptions about their prior knowledge before entering the undergraduate classroom.

Even at the undergraduate level, evolution is rarely presented as a unifying theme for understanding biology, despite its pervasiveness as an explanatory construct across biological research. Instead, evolution is generally taught as a distinct topic without explicitly making it clear how it plays a role in other biological concepts and processes. This is reflected in the structure of textbooks frequently used in undergraduate biology instruction and in the syllabi derived from them ( Nehm et al. , 2009 ). Additionally, in the context of this particular study, while “Evolution” is one of the core concepts in Vision and Change ( AAAS, 2011 ), the report does not refer to human evolution either (to be fair – it does not use any other taxa as a reference either).

Such differences in the quantity and quality of students’ prior evolutionary knowledge at both the K-12 and undergraduate levels could explain students’ susceptibility to contextual influences as well as the difficulty associated with changing students’ mental models of evolution that have been shaped by years of exposure and experiences.

Students’ scientific expertise.

As novice science learners, students may be more sensitive to contextual influences when learning complex concepts, such as evolution. There are major differences between the way experts and novices approach problem solving in any field. Experts have a deeper conceptual understanding of their subject matter which enables them to be flexible in identifying and retrieving bits of relevant knowledge. This leads experts to intuitively see patterns that novices are unable to discern ( NRC, 2000 ). Additionally, experts are more able to identify and focus on the abstract principles that underlie a problem’s structure while novices tend to focus on more superficial features ( Chi et al. , 1981 ; Hmelo-Silver and Pfeffer, 2004 ; Nehm and Ridgway, 2011 ). As novices, it is not surprising that students are influenced by prompt contexts. However, our data suggest that instruction can decrease students’ sensitivity to context, perhaps indicating they are making progress in their transition from novice to expert.

Implications for instruction and assessment

Multiple studies that have looked at different instructional strategies and contexts and have shown varying levels of improvements in students’ understanding of evolution in general ( Bray Speth et al. , 2009 , 2014 ; Kampourakis and Zogza, 2009 ; Aptyka et al. , 2022 ; Nehm et al. , 2022 ; Sbeglia and Nehm, 2022 ), and human evolution in particular ( Alters and Nelson, 2002 ; Kalinowski et al. , 2010 ; Bravo and Cofré, 2016 ; Pobiner, 2016 ; Pobiner et al ., 2018 ).

Many researchers have called for evolution to be taught using humans as a focal organism. Nettle (2010) showed gains in student understanding of evolution in general after students were taught evolution in the context of humans. Pobiner et al. (2018) and Pobiner (2016) propose teaching about human evolution as a direct and effective way to decrease barriers to accepting and subsequently understanding evolution. However, Beggrow and Sbeglia (2019) did not find any particular affordances offered by teaching evolution in a human context. Deeper learning can result when the learner identifies with the subject matter and finds it relevant ( NRC, 2009 ). Therefore, because students are highly likely to find themselves and their development interesting ( Pobiner et al. , 2018 ), teaching evolution in the human context could mean that students find it relevant and identify with it. We would like to offer the suggestion that while teaching evolution in a solely human context is not optimal, including humans as one of the contexts could be very important.

At various institutions and at the national level, numerous efforts are underway to renovate and align the biology core curriculum. In particular, there is considerable interest in increasing the prominence of science practices as an explicit objective at all levels to teach science as it is practiced and to encourage students to think and reason about science similar to practitioners ( AAAS, 2011 ; Cooper et al. , 2015 ). A lack of scientific accuracy in students’ reasoning is often not because of a lack of knowledge of the scientific principles, but due to inadequate activation, recruitment, or transfer of those scientific principles across contexts ( Brown et al. , 1989 ; Clark, 2006 ; Clartcey, 2009 ; Nehm and Ha, 2011 ; diSessa, 2013 ; Aptyka et al. , 2022 ). Multiple recent meta-analyses have shown that instructional models that incorporate active learning improve student learning gains broadly ( Freeman et al. , 2014 ; Shi et al. , 2020 ; Theobald et al. , 2020 ; Bredow et al. , 2021 ). Additionally, studies that have used the ACORNS instrument to measure learning gains of active learning strategies in evolution classrooms have shown similar results ( Cofré et al. , 2017 , 2018 ; Nehm et al. , 2022 ). Our study, as well as that of Bray Speth et al. (2014) , showed gains in student performance in understanding variation after a semester of active learning that incorporated modeling-based practices. Perhaps by using scientific practices such as data analysis, modeling, and argumentation during active learning instruction, and including humans as an instructional context, will lead to a deeper, more conceptual understanding of evolution, an increased ability to transfer relevant concepts, and thereby decrease susceptibility to contextual influences.

Finally, our findings have clear implications for assessment. A common strategy in university classrooms is to design parallel, or alternative, versions of assessments for the purpose of creating multiple exam forms or assessing concepts using contexts that are different from those used during instruction. It is generally assumed that these minor variations are of little significance when measuring learning outcomes. The assumption is that students will identify the underlying concepts being assessed, recruit the relevant knowledge, and transfer it to the new context. However, it has been established that ensuring parallel prompts are equivalent in terms of difficulty is both important and challenging to accomplish ( Hamp-Lyons and Mathias, 1994 ; Lee and Anderson, 2007 ; Sydorenko, 2011 ; Li, 2018 ). The prompts used in our study were designed not just to test for equivalent content but were truly isomorphic, in that they utilized the same prompt stem. The words that varied were also remarkably similar in that both taxa were mammals, close in evolutionary terms ( Kumar et al. , 2017 ), and familiar to students ( Nehm et al. , 2012 ). However, despite the high degree of prompt similarity, we still saw differences in student responses based on seemingly minor variations in context. Our data, as well as the broader corpus of findings about contextual influences, suggest that assumptions about equivalence among assessments that vary in context are frequently unwarranted. Care must be taken to ensure assessments are fair and unbiased − particularly in high-stakes situations, such as exams or when the assessments are linked to rewards or inclusion in programs or other educational opportunities. To buffer against contextual effects, instruction should feature multiple contexts of the same concept or phenomenon and instructors should provide explicit guidance that distinguishes the underlying principles that transfer across contexts.

Limitations and Future Directions

Due to the constraints of the study design, the degree to which the findings of this study can be generalized is difficult to predict. We compared student responses to prompts about trait gain in two taxa (cheetah and human) and are therefore unable to say how our findings might apply to other taxa that are at different evolutionary distances from humans, or whether students would respond similarly about trait loss. Such systematic comparisons could be explored through the design of multiple prompts varying in evolutionary distance and administered across a large sample of students.

Students’ responses were coded by an online automated response tool (EvoGrader) that only identified the presence/absence of six key concepts and three naïve ideas with respect to evolution. Additional evolutionary concepts (including threshold concepts) or other biologically relevant information (e.g., the level of biological organization at which variation occurs) may have been present in student responses but were not considered in our assessment of outcomes. Similarly, students’ use of language and consistency in their application of KCs and NIs at different points in their narratives were not considered and could potentially influence interpretation of students’ meaning.

This study did not explore whether there are patterns in susceptibility to contextual influences based on demographic characteristics (e.g., sex, race, grades, etc.). Such information could be useful when designing assessments that aim to be fair, accessible, and unbiased in their potential to measure student learning.

Finally, our study reports findings from one introductory biology course taught by one instructor. Although the course had been transformed to be active, learner-centered, and used evidence-based pedagogies, such as cooperative learning, high-frequency low-stakes assessment, and an emphasis on science practices, it was not designed to explicitly test any particular hypothesis about contextual susceptibility. As such, we can neither claim that our findings are broadly generalizable across other course contexts or instructors, nor can we point to specific causal mechanisms underlying the patterns we observed. Identifying the mechanisms that explain how and why students do or do not succumb to minor variations in context will be a significant and impactful contribution to literature, but will require multiple systematically designed studies to do so.

ACKNOWLEDGMENTS

We thank Mitch Distin for his contributions to conceptualizing and designing the study and for help with data collection; Etiowo Usoro and Patrycja Zdziarska for logistical and technical support throughout the project; Mridul Thomas for help with data analysis; and Melanie Cooper, Amelia Gotwals, and Katherine Gross for comments on earlier versions of the manuscript. We also thank Francesco Pomatti and Anita Narwani at the Department of Aquatic Ecology at Eawag, Switzerland for providing space and resources while writing this manuscript. We gratefully acknowledge all the students whose anonymous assessments were used in this study. Finally, we would like to point out that it is not “tea” unless it is made with the leaves of Camellia sinensis.

This is Kellogg Biological Station Contribution No. 2365. This material is based in part upon research supported by the National Science Foundation under grant numbers DRL 1420492, DRL 0910278, DUE 2012933, and DBI-0939454. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Submitted: 3 June 2021 Revised: 24 August 2023 Accepted: 8 September 2023

© 2023 J. de Lima and T. M. Long. CBE—Life Sciences Education © 2023 The American Society for Cell Biology. This article is distributed by The American Society for Cell Biology under license from the author(s). It is available to the public under an Attribution–Noncommercial–Share Alike 4.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/4.0).

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Understanding Evolution

Your one-stop source for information on evolution

Teaching Resources Database

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Grade level

Found 101 resources:

La Supervivencia del más Astuto

Grade Level(s):

• UC Museum of Paleontology

Resource type:

Time: 10 minutes

Este cómic nos habla de los esfuerzos de un grillo macho para atraer a una pareja. Y en el proceso, revela (destruye) algunos típicos malentendidos sobre lo que significa estar evolutivamente “adaptado”.

View details »

Semejanzas y diferencias: Comprendamos las homologías y evolución convergente (nivel secundaria)

• Online activity or lab

Time: 30 minutes

Esta investigación interactiva explica qué son las homologías, cómo reconocerlas y cómo es que evolucionan.

Semejanzas y diferencias: Comprendamos las homologías y evolución convergente (nivel bachillerato)

Artificial selection with elaine ostrander and team.

• Classroom activity

In this article (and the linked assignments and student readings), students examine and interpret data that the team used to study the genes undergoing artificial selection during the development of different dog breeds. Use the tabs at the bottom of the feature to find related videos, assignments, and lessons to build this example into a lesson sequence on artificial selection.

Sexual Selection with Maydianne Andrade

Time: 1 hour

In this article (and the linked assignments and student readings), students examine and interpret data that Maydianne collected to help her figure out why redback spiders evolved a mating behavior in which the male spider is often killed by the female spider. Use the tabs at the bottom of the feature to find related videos, assignments, and lessons to build this example into a lesson sequence on sexual selection.

Mecanismos: Los procesos de la evolución

Time: Varies

Aprende sobre los procesos básicos que han moldeado la vida y producido su asombrosa diversidad. Este artículo se encuentra en Evolución 101 .

Selección natural

Time: 30-40 minutes

La idea más famosa de Darwin, “La selección Natural”, explica la gran diversidad de la vida. Aprende cómo funciona, explora algunos ejemplos, y descubre cómo evitar falsas ideas. Este artículo se encuentra en Evolución 101 .

Evo in the news: Human evolutionary history impacts our COVID-19 risk

• Evo in the News article

This news brief from November 2020 explains how a gene from Neanderthals made its way into human populations and now affects COVID-19 risk.

La historia evolutiva del ser humano afecta nuestro riesgo de padecer COVID-19

Este resumen de noticias de noviembre de 2020 explica cómo un gen de los Neandertales que se introdujo en las poblaciones de los humanos modernos, afecta al riesgo de padecer COVID-19.

Mate choice and fitness consequences

• Annotated journal article

Students read a 2005 paper on the fitness consequences of mate choice alongside an interactive guide that asks the reader to answer key questions about each section of the article.

Selection and evolution with a deck of cards

• Evolution: Education and Outreach

Time: 1-2 class periods

This classroom exercise introduces the concept of evolution by natural selection in a hypothesis-driven, experimental fashion, using a deck of cards.

Natural Selection & Sexual Selection: An Illustrated Introduction

• Cornell Lab of Ornithology

Time: 15 minutes

This illustrated video explores how natural and sexual selection can shape the way animals look and act, sometimes transforming the drab into the magnificent. To access the associated multiple choice and open answer questions, you'll need to register with the site.

Hardy-Weinberg Equilibrium According to Hoyle

• Cronkite, Donald

Time: One class period

Students achieve an understanding of the Hardy-Weinberg Equilibrium by using decks of playing cards without recourse to algebra.

Stickleback Evolution Virtual Lab

• Howard Hughes Medical Institute

Time: 3 hours

This virtual lab teaches skills of data collection and analysis to study evolutionary processes using stickleback fish and fossil specimens.

Spoons, forks, chopsticks, straws: Simulating natural selection

• Kathryn Flinn

Time: 50 minutes

In this classroom activity, students participate in demonstrating how natural selection works. They play the roles of predators with different feeding appendages (spoons, forks, chopsticks, or straws) and compete to gather beans as prey.

Similarities and differences: Understanding homology and convergent evolution

This interactive investigation explains what homologies are, how to recognize them, and how convergent traits evolve.

Relevance of evolution: Medicine

Explore just a few of the many cases in which evolutionary theory helps us understand and treat disease. Bacterial infections, HIV, and Huntington's disease are highlighted.

Problem-based discussion: Natural selection in Darwin’s finches

Time: 5-20 minutes

This set of two PowerPoint slides featuring questions for problem-based discussion (i.e., open-ended questions that engage students with each other and with course material) can be easily incorporated into lectures on natural selection.

Preying on Beans

Time: 50-60 minutes

Students act as predators searching for prey (beans) in two different settings to demonstrate the processes of adaptation and selection.

Population genetics, selection, and evolution

Time: Two to three 50-minute class periods

This hands-on activity, used in conjunction with a short film, teaches students about population genetics, the Hardy-Weinberg principle, and how natural selection alters the frequency distribution of heritable traits. It

Origami Birds

Time: Three to four class periods

Students build and evolve and modify paper-and-straw "birds" to simulate natural selection acting on random mutations.

Natural selection: The basics

Darwin's most famous idea, natural selection, explains much of the diversity of life. Learn how it works, explore examples, and find out how to avoid misconceptions. This article is located within Evolution 101 .

Natural selection from the gene up: The work of Elizabeth Dahlhoff and Nathan Rank

• Research profile

Find out how we investigate evolutionary adaptations by following two scientists and their team as they figure out how the willow leaf beetle survives in different climates.

Natural selection and evolution of rock pocket mouse populations

This lesson serves as an extension to the Howard Hughes Medical Institute short film The Making of the Fittest: Natural Selection and Adaptation. It provides an opportunity for students to analyze amino acid data and draw conclusions about the evolution of coat-color phenotypes in the rock pocket mouse.

Natural selection and adaptation slide set

Time: 2 minutes

This set of five PowerPoint slides featuring personal response questions (i.e., multiple choice questions that can be used with "clicker" technology) can be incorporated into lectures on natural selection and adaptation in order to actively engage students in thinking about evolution.

The Natural Selection Game

• Gendron, Robert

Time: 1 to 2 class periods

This is a board game that simulates natural selection. It is suitable for an introductory biology class and for more advanced classes where you could go into more detail on important principles such as the role of variation and mutation.

Molecular genetics of color mutations in rock pocket mice

This lesson requires students to transcribe and translate portions of the wild-type and mutant rock pocket mouse Mc1r genes and compare sequences to identify the locations and types of mutations responsible for the coat color variation described in a short film.

The Making of the Fittest: Natural Selection and Adaption

This 10-minute film describes the research of Dr. Michael Nachman and colleagues, whose work in the field and in the lab has documented and quantified physical and genetic evolutionary changes in rock pocket mouse populations.

Mechanisms of evolution slide set

This set of three PowerPoint slides featuring personal response questions (i.e., multiple choice questions that can be used with "clicker" technology) can be incorporated into lectures on the mechanisms of evolution in order to actively engage students in thinking about evolution.

The Evolution Lab

• Lab activity

The Evolution Lab contains two main parts. In the first, students build phylogenetic trees themed around the evidence of evolution, including fossils, biogeography, and similarities in DNA. In the second, students explore an interactive tree of life and trace the shared ancestry of numerous species.

Mechanisms of evolution

Learn about the basic processes that have shaped life and produced its amazing diversity. This article is located within Evolution 101 .

The Beetle Project: Investigating insects in a warming world

Time: 30 min to 10 class periods

This adaptable instructional module uses insects as a model system to illustrate the biological impacts of climate change, with the goal of engaging students with a range of hands-on and minds-on activities that increase their understanding of how science works, evolutionary processes, and the impacts of climate change.

• Smithsonian National Museum of Natural History

Time: Seven 50-minute class periods

In this advanced 4-lesson curriculum unit, students examine evidence to compare four different explanations for why many malarial parasites are resistant to antimalarial drugs; investigate how scientific arguments using G6PD data show support for natural selection in humans; design an investigation using a simulation based on the Hardy-Weinberg principle to explore mechanisms of evolution; and apply their understanding to other alleles that have evolved in response to malaria.

Testing a hypothesis

Students watch a short film about natural selection in humans and answer questions on a worksheet that reinforce the evolutionary story behind malaria and sickle cell anemia prevalence.

Investigating Natural Selection

• National Academy of Sciences

Time: Three class periods

Students experience one mechanism for evolution through a simulation that models the principles of natural selection and helps answer the question: How might biological change have occurred and been reinforced over time?

High altitude adaptations: The work of Emilia Huerta-Sánchez

This research profile follows statistician and population geneticist Emilia Huerta-Sánchez as she studies the adaptations that allow Tibetan highlanders to live 13,000 feet above sea level without developing altitude sickness.

Fire ants invade and evolve

Time: 40 minutes

Understanding the evolution of fire ants may help scientists control the spread of these pests, which have already taken over much of the U.S.

Evolution connection: Transcription and translation

• Evo Connection slide set

Time: 5 minutes

This short slide set relates the role of RNA in the processes of transcription and translation to RNA's evolutionary history and the remnants of the RNA world. Save the slide set to your computer to view the explanation and notes that go along with each slide.

Evolution connection: Proteins, carbohydrates, and nucleic acids

This short slide set weaves basic information about carbohydrates, proteins, and nucleic acids into one evolutionary story regarding the evolution of lactose tolerance, which relates to students' everyday lives. Save the slide set to your computer to view the explanation and notes that go along with each slide.

Evolution of human skin color

Time: Seven to ten 50 minute class periods

Students examine evidence for the relationship between UV and melanin in other animals; investigate the genetic basis for constitutive skin color humans; learn to test for natural selection in mouse fur color; investigate how interactions between UV and skin color in humans can affect fitness; and explore data on migrations and gene frequency to show convergent evolution of skin color.

Evolution and E. coli: Natural selection in a constant environment

In this reading-, writing-, and discussion-based activity, students explore bacterial evolution occurring in a stable environment, which counters the intuitive misconception that environmental change is a necessary component to natural selection. A landmark study provides the backdrop against which students can challenge their thinking about what it means for a population to evolve.

Evolution and Antibiotic Resistance

Time: One to three class periods

Students learn why evolution is at the heart of a world health threat by investigating the increasing problem of antibiotic resistance in such menacing diseases as tuberculosis.

Evolution 101

Time: multiple days

This in-depth, multi-part course takes you through evolutionary theory and mechanisms, from definitions to details, natural selection to genetic drift, mutations to punctuated equilibrium.

Evolución 101

¿Qué es la evolución y cómo funciona? Introducción a la evolución ofrece información detallada y práctica sobre los patrones y los mecanismos de la evolución.

Evo in the News: When fighting leukemia, evolutionary history matters

This news brief, from December 2011, describes how evolutionary history can factor into the success of a bone marrow transplant.

Evo in the news: Warming to evolution

Global warming increasingly affects many aspects of our environment, from the sea level to tropical storm strength. But that's far from the full story. This news brief from July 2006 describes how global warming has already begun to affect the evolution of several species on Earth.

Evo in the news: Toxic river means rapid evolution for one fish species

This news brief from March 2011 examines the genetic basis for the evolution of resistance to PCBs in the Hudson River tomcod. Though this is great for the tomcod, what might it mean for other organisms in the ecosystem?

Evo in the news: The recent roots of dental disease

Time: 20 minutes

This news brief from March 2013 describes new research suggesting that human dietary changes associated with the invention of agriculture and the Industrial Evolution caused an epidemic of tooth decay and gum disease. This link between diet and oral health is an example of a mismatch to modernity, a case in which a disease results from a modern lifestyle feature that our lineage has not experienced during the course of its evolutionary history.

Visualizing life on Earth: Data interpretation in evolution

Time: 2 hours

This web-based module leads students through an exploration of the patterns in the diversity of life across planet Earth. Students are scaffolded as they practice data interpretation and scientific reasoning skills.

Viruses and Host Evolution

• Chamberlain, Don

Time: Four class periods

Students learn about natural selection in rabbits by observing the effects of a virus on the Australian rabbit population.

Evo in the news: Superbug, super-fast evolution

Methicillin-resistant staph infections now contribute to more US deaths than does HIV. This news brief from April of 2008 explains the quirks of bacterial evolution that make them such a threat.

Evo in the news: Sex, speciation, and fishy physics

More than 500 species of cichlid fish inhabit Africa's Lake Victoria. This news brief from March 2009 explains new research suggesting that the physics of light may have played an important role in cichlid diversification and in the recent drop in their diversity.

Evo in the news: Seeing the tree for the twigs

Recent research has revealed that, in at least some ways, chimpanzees have evolved more than humans have. This news brief from May 2007 delves into this finding further and, in the process, debunks common misperceptions of human evolution.

Variations in the clam species Clamys sweetus

Time: 3 x 45-minute sessions

This series of hands-on activities complements the HHMI DVD Evolution: Constant Change and Common Threads and has been designed to engage students in thinking about the mechanism of natural selection by encouraging them to formulate questions that can be answered through scientific investigation, data collection, and pattern recognition.

Evo in the news: Quick evolution leads to quiet crickets

The tropical island of Kauai has always been a quiet place, but now it may be getting even more quiet. This news brief, from December 2006, reveals how Kauai's cricket population has evolved into a "chirpless" variety in just a few years.

Evo in the news: No more mystery meat

This news brief from April 2013 describes new research on the origin of American cattle breeds. The story told by the cows' genes crisscrosses the trajectory of human evolutionary history from wild aurochs that lived alongside Neanderthals, to Christopher Columbus and, ultimately, the American West.

Evo in the news: Musseling in on evolution

This news brief, from September 2006, reviews a recent case of evolution in action. In just 15 years, mussels have evolved in response to an invasive crab species. Find out how biologists uncovered this example of evolution on double time.

Variability and Selection in Natural Populations of Wood Lice

• Berkelhamer, Rudi

Time: 3-hour lab

In this lab, students measure the amount of variation in a natural population of terrestrial wood lice and then determine which traits are subject to selection by predators by performing a simulated predation experiment.

Evo in the news: Livestock kick a drug habit

This news brief, from September of 2005, describes the FDA ban on the use of the antibiotic Baytril in poultry production. The decision was made in order to reduce the danger presented by the evolution of antibiotic resistant bacteria.

Evo in the news: Influenza, an ever-evolving target for vaccine development

Some vaccines provide lifelong protection with one or a few doses, but the flu requires a new shot every year. And in some years, the flu shot is hardly effective at all. Why is the flu vaccine different from so many other vaccines? This news brief from February 2013 provides the evolutionary explanation.

Evo in the News: Hybrid sharks aren’t “trying” to adapt

This news brief, from February 2012, describes the discovery of hybrid sharks in Australian waters, debunks some common misconceptions regarding the discovery, and examines the possible evolutionary trajectories of these animals.

Evo in the News: Grasshoppers change their tune. Is it evolution in action?

This news brief, from December 2012, describes new research into how traffic noise affects insect populations. Several hypotheses to explain the change in grasshoppers' songs are examined.

Evo in the news: Got lactase?

The ability to digest milk is a recent evolutionary innovation that has spread through some human populations. This news brief from April 2007 describes how evolution has allowed different human populations to take advantage of the nutritional possibilities of dairying and links evolution with the prevalence of lactose tolerance among people of different ethnicities.

Evo in the news: Ghosts of epidemics past

HIV and malaria both constitute global health threats, respectively affecting more than 30 million and 200 million people worldwide. This news brief from October 2008 describes new research that reveals an unexpected evolutionary link between the two.

Evo in the news: Fighting the evolution of malaria in Cambodia

This news brief from December 2009 focuses on one of the world's most deadly infectious diseases: malaria. Malaria is normally treatable, but now some strains are evolving resistance to our most effective drug. Find out how researchers and doctors are trying to control the evolution of the disease.

Evo in the news: Evolving altitude aptitude

This news brief from October 2010 examines new research that makes it clear that Tibetan highlanders have not just acclimated to their mountain home; evolutionary adaptations have equipped them with unique physiological mechanisms for dealing with low oxygen levels.

Evo in the News: Evolutionary history in a tiny package

This news brief, from March 2012, describes the discovery four new species — all miniature chameleons — and explores the concept of island dwarfism.

Evo in the news: Evolution’s dating and mating game

This news brief from May of 2008 describes new research on octopus mating and reveals how evolution can favor some surprising courtship behaviors.

Evo in the news: Evolution in the fast lane?

Have humans, with all of our technological advances, exempted ourselves from further evolution? Perhaps not. This news brief, from February 2008, examines genetic research which suggests that human evolution may haved actually accelerated in our recent history.

Evo in the news: Evolution down under

This news brief, from September of 2008, describes an unusual contagious cancer currently decimating Tasmanian devil populations. Learn about the fascinating interplay between the evolution of the devils and the evolution of the disease.

Evo in the news: Evolution and the avian flu

This news brief, from November of 2005, describes the threat of avian flu. The stage is set for this virus to evolve into a strain that could cause a deadly global pandemic.

Evo in the news: Conserving the kakapo

This news brief, from April 2006, chronicles how researchers are using evolutionary theory to guide their strategies for conserving a critically endangered parrot - with some impressive results!

Evo in the news: Better biofuels through evolution

This news brief from April 2009 describes how synthetic biologists are using the process of directed evolution to improve the efficiency of biofuel production.

Evo in the news: Bed bugs bite back thanks to evolution

This news brief of September 2010 examines the resurgence of bed bugs throughout the country, and the real bad news is that those bed bugs have evolved resistance to the chemicals most commonly used for eradication.

Evo in the news: Antibiotic resistant bacteria at the meat counter

This news brief from May 2013 describes research showing that a large percentage of the meat in supermarkets is contaminated with antibiotic resistant bacteria. An evolutionary perspective explains how antibiotic resistance arises in the first place and why the prevalence of resistant bugs in livestock has health professionals and scientists worried.

Evo in the news: Another perspective on cancer

This news brief, from October of 2007, describes the evolutionary underpinnings of cancer. Recognizing cancer as a form of cellular evolution helps explain why a cure remains elusive and points the way toward new treatments.

Evo in the News: Acidic oceans prompt evolution

This news brief, from October 2012, describes new research into the evolutionary response that ocean acidification may prompt in some plankton species.

Comic strip: Survival of the sneakiest

This comic follows the efforts of a male cricket as he tries to attract a mate, and in the process, debunks common myths about what it means to be evolutionarily "fit."

Color variation over time in rock pocket mouse populations

Students watch a short film and complete a worksheet and graphing exercise that reinforces the concepts of variation and natural selection.

Students learn about variation, reproductive isolation, natural selection, and adaptation through this version of the bird beak activity.

Candy Dish Selection

• Tang, Carol

Students find that selection occurs in a dish of mixed candies.

Breeding Bunnies

Students simulate breeding bunnies to show the impact that genetics can have on the evolution of a population of organisms.

Artificially Selecting Dogs

• Collins, Jennifer

Time: 90 minutes

Students learn how artificial selection can be used to develop new dog breeds with characteristics that make the dogs capable of performing a desirable task.

Angling for evolutionary answers: The work of David O. Conover

Human activity has certainly affected our physical environment - but it is also changing the course of evolution. This research profile follows scientist David O. Conover as he investigates the impact of our fishing practices on fish evolution and discovers what happened to the big ones that got away.

Aloha, spider style! The work of Rosemary Gillespie

Time: one class period

This research profile follows Dr. Rosemary Gillespie to Hawaii as she evaluates hypotheses about the evolution of the colorful happy-face spider.

Allele and phenotype frequencies in rock pocket mouse populations

Time: One or two class 50-minute periods

This video and worksheet use real rock pocket mouse data collected by Dr. Michael Nachman and his colleagues to illustrate the Hardy-Weinberg principle.

Adaptation: The case of penguins

• Visionlearning

The process of natural selection produces stunning adaptations. Learn about the history of this concept, while you explore the incredible adaptations that penguins have evolved, allowing them to survive and reproduce in a climate that reaches -60°C!

This article appears at Visionlearning.

What did T. Rex Taste Like?

Time: 2-4 hours

In this web-based module students are introduced to cladistics, which organizes living things by common ancestry and evolutionary relationships.

Webcast: Selection in action

• Video Lecture

Time: 60 minutes

In lecture two of a four part series, evolutionary biologist David Kingsley discusses how just a few small genetic changes can have a big effect on morphology, using examples from maize, dog breeding, and stickleback fish.

This lecture is available from Howard Hughes' BioInteractive website.

Webcast: Endless forms most beautiful

In lecture one of a four part series, evolutionary biologist Sean Carroll discusses Darwin and his two most important ideas: natural selection and common ancestry.

Darwin and Wallace: Natural selection

Darwin and Wallace came up with the idea of natural selection, but their idea of how evolution occurs was not without predecessors.

This article is located within  History of Evolutionary Thought .

Big Beans, Little Beans

Time: Variable

Students measure and note the variation in the lengths of lima beans. Students then compare the growth rate of different sized beans.

Battling bacterial evolution: The work of Carl Bergstrom

This research profile examines how the scientist Carl Bergstrom uses computer modeling to understand and control the evolution of antibiotic resistant bacteria in hospitals.

Battle of the Beaks

Time: Two class periods.

Students learn about adaptive advantage, based on beak function, by simulating birds competing for various foods.

Adaptation to altitude

Time: Eight 50-minute class periods

In this set of sequenced lessons, students learn how to devise an experiment to test the difference between acclimation and adaptation; investigate how scientific arguments show support for natural selection in Tibetans; design an investigation using a simulation based on the Hardy-Weinberg principle to explore mechanisms of evolution; and devise a test for whether other groups of people have adapted to living at high altitudes.

A look at linguistic evolution

We typically think of evolution occurring within populations of organisms. But in fact, evolutionary concepts can be applied even beyond the biological world. Any system that has variation, differential reproduction, and some form of inheritance will evolve if given enough time. Find out how an understanding of evolution can illuminate the field of linguistics.

This article appears at SpringerLink.

Las chinches de cama pican de nuevo gracias a la evolución

Las chinches de cama puede parecer un viejo problema pasado de moda, sin embargo ahora están de vuelta — y con venganza. Hace cincuenta años, estas plagas chupadoras de sangre estaban casi erradicadas en los Estados Unidos gracias, en parte, al uso de pesticidas como el DDT. Hoy, se arrastran entre las sabanas — y atormentan a los desgraciados soñadores — en todo el país...

Juego evolutivo de citas y apareamiento

Largamente asumidos como solitarios, al menos una especie de pulpo lleva una compleja vida amorosa. El mes pasado, los biólogos Christine Huffard, Roy Caldwell y Farnis Boneka reportaron los resultados de los primeros estudios a largo plazo sobre el comportamiento de apareamiento de pulpos en la naturaleza...

Sexo, especiación y física subacuática

Evolución en las noticias relata una reciente historia que señala como comprender física básica puede revelar como la evolución esta ocurriendo hoy — en especial, como la física de la luz tiene influencia sobre la selección sexual, especiación y el colapso de la biodiversidad, producto de la polución causada por los humanos...

Mejores biocombustibles gracias a la evolución

Actualmente, la mayoría de nosotros llenamos nuestro tanque de gasolina con combustibles fósiles, es decir, restos de plantas y animales que murieron muchos millones de años atrás y eventualmente se convirtieron en petróleo — pero, por supuesto, esto no puede perdurar para siempre. El petróleo es un recurso limitado y en algún momento se va a terminar. Para ayudar a solucionar este problema, muchos científicos, políticos, gente de negocios y ciudadanos preocupados han puesto sus esperanzas en los biocombustibles...

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 7, introduction to evolution and natural selection.

• Natural selection and the owl butterfly
• Biodiversity and natural selection
• Variation in a species
• Darwin, evolution, & natural selection
• Natural selection

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Video transcript