In this chapter students will learn:

• why it is important to understand evolutionary theory.
• the nature of science.
• the history of evolutionary thought.
• the basics of evolutionary theory.
• that mutations are key to evolution in all life forms ranging from the creation of new strains of a virus to the evolution of humans.

Introduction
Evolution is a fact. Nothing makes sense about human biology unless we understand evolution. Science is a good framework for understanding evolution.

The Nature of Science
Science is a framework with principles, methods, and ways of evaluating explanations.

History of Evolutionary Thought and Theory
Key people in the history of evolutionary thought include John Ray, Carolus Linnaeus, George Buffon, Jean-Baptiste Lamarck, James Hutton, Charles Lyell, Charles Darwin, Alfred Wallace, and Gregor Mendel. Darwin developed the theory of evolution by natural selection. Mendel provided the foundation for understanding genetics.

Modern Evolutionary Theory
Modern evolutionary theory builds on the work of Darwin and Mendel, including an understanding of how variation occurs, is selected, and is distributed. It includes the ideas and concepts of mutations, natural selection, sexual selection, inheritance, gene flow, genetic drift, adaptive radiation, and epigenetics.

1. What are the principles and methods of science?

2. Who were the key people in the development of evolutionary theory before 1859, and what were their contributions?

3. What are the key elements of Darwin’s Theory of Evolution by Natural Selection?

4. What was the contribution of Gregor Mendel to evolutionary theory?

5. What is the braided stream model of evolution?

6. What is the modern evolutionary synthesis, and how may it be distinguished from the extended evolutionary synthesis?

1. If you could go back in time, with whom would you rather have a conversation—Darwin, Wallace, or Mendel? Why?

2. What are some problems predicting how any kind of plant or animal species will continue to evolve biologically?

3. What are the implications of genetic engineering for the future of humanity?

4. How can the emergence and spread of COVID-19 be explained using the concepts outlined in this chapter?

adaptive radiation a process by which one species occupies a new ecological niche, quickly increasing its population and diversifying into new species

allele an alternate form of a gene

allele frequency the relative proportion of a particular allele occurring, compared to other alleles that could be selected

BCE "Before the Common Era," a secular calendar notation equal to BC/p>

CE "Common Era," a secular calendar notation equal to AD

COVID-19 the acronym given to the disease caused by a new coronavirus frist identified in 2019; COVID-19 created a global pandemic

DNA deoxyribonucleic acid; a molecule that contains the genetic instructions for living organisms

epigenetics the study of how parts of the genome may become activated or deactivated as an organism develops

extinctions that which occurs when a taxanomic group, usually a species, ceases to exist, either because it could not adapt to changing circumstances or because it evolved into a new species

gene a unit of heredity

gene flow the movement of genes between populations

genetic drift the random factor in evolution, including changes in allele frequencies by chance rather than selection

genetics the study of a particular gene or groups of genes, especially as it relates to inheritance

genome the complete genetic make-up of an organism

genomics the study of genomes

genotype the genetic make-up of an organism

genus a taxonomic category, above the level of species

gradualism the idea that evolutionary change is a long, slow process

hypothesis a possible explanation that may be tested using scientific methods

Inheritance of Acquired Characteristics the (incorrect) idea that characteristics acquired during one’s lifetime could be passed on to offspring

mass extinctions widespread and rapid extinctions, usually restricted to situations in which at least half of all living species become extinct

mutation an error in the replication of DNA

phenotype the physical expression of a genotype; what an organism looks like

punctuated equilibrium the idea that evolutionary change may alternate between periods of slow, gradual change and short periods of significant change

science a framework for investigating and understanding things, including a specific set of principles and methods

sexual selection when mates are chosen based on characteristics unrelated to survival

species a population that can mate and produce fertile offspring in natural conditions

speciation the evolution of new species or the process of creating species

theory in science, an extremely well-supported idea; an idea that has not been disproven

uniformitarianism the idea that the processes that created landscapes of the past are the same processes in operation today

Creation (movie). 2009. BBC Film.

Gould, S.J. (1997). Nonoverlapping Magisteria. Natural History 106 (March): 16-22.

Weiss, K.M., & Buchannon, A.V. (2009). The Mermaid’s Tale: Four Billion Years of Cooperation in the Making of Living Things. Cambridge, MA: Harvard University Press.

Darwin Online
darwin-online.org.uk

The Mermaid’s Tale (blog)
ecodevoevo.blogspot.ca

1. In what ways could the human design be bettered? How might those changes come about?

2. If someone gave you a plant with recessive red flowers, and another plant of the same kind with dominant blue flowers, and you interbred them, what color flowers would you expect to see and why?

3. How do Darwin’s research and publications affect our understandings of humans? If Darwin had never existed, how might our understandings today be different?

4. If any one of the steps in the scientific method were to be erased or ignored, how would this affect the quality of research being conducted?

5. Rather than through Darwin’s understanding of evolution, assume Lamarck’s Theory of the Inheritance of Acquired Characteristics were fact. How might you expect the human species to evolve?

6. If you were told that a new species of dog had just been discovered because of mutations within a previously existing species, what might you think?

7. Describe two scenarios involving a single species of bear: one in which they are subject to genetic drift, and another in which there is significant gene flow. Would they speciate, and how would these scenarios differ?

8. In what ways have humans contributed to species going extinct?

9. Do science and the theory of evolution disprove religious ideologies and beliefs? Justify your answer.

10. Imagine that during the last mass extinction 65 million years ago, the asteroid instead caused significantly less environmental changes. Additionally, dinosaurs had stronger requisite variability. What would change today and why?

Answers

1. This answer can vary significantly. It should demonstrate a general understanding of how evolution occurs (e.g., that it is not following the giraffe-neck process as in the theory of the inheritance of acquired characteristics).

• The example in the text is about bipedalism and how, as people age, this mechanism does not hold up well (hips, feet, knees, back). Bipedalism provides many advantages, but evolutionary measures like this come with consequences.
• Building on the bipedal example, you could describe how joint sockets (like the knee or hip) could evolve into something more stable (whether a bone formation mutation, or a different skeletal arrangement, etc.).
• Another example could build on the ability to digest lactose (or the digestive system overall, eliminating illnesses like Celiac disease). Examples can be unrelated to text examples, as long as they are reasoned out.

See page 58 of your text.

2. This answer could be red, blue, purple, or another color—the main point is how it is justified, showing a comprehensive understanding of Mendelian genetics (and its limitations).

• For example, if you chose the color blue, you should explain that the flowers were known to be pure strains of a plant that are known to have binary genotypes and phenotypes (i.e., the only possible colors for flowers are red and blue).
• The 3:1 ratio that Mendel discovered should also be referenced, relative to the color choice, and why and how other colors could result.

See pages 68–69 of your text.

3. Answers should include:

• Although Darwin did not specifically focus on humans in his seminal work, his later works explicitly discuss the implications of evolutionary theory.
• His works helped cement the knowledge that humans are part of the animal world and subject to the same processes witnessed in nature. This affects how we understand not only biology but also culture, so there are many implications.
• Without Darwin, the evolutionary theory would have still entered public knowledge, since it is based on empirical evidence. Wallace, another researcher at the time, came to the same conclusions as Darwin, so our understandings would likely be the same. However, if neither researcher had lived at that particular time, evolutionary theory would likely still have arisen, but at a later time; the timing of such research does make a difference on how it is received, so one can speculate on the differences this would have made.

See pages 63–67 of your text.

4. The answer should be able to spell out the four key steps of the scientific method, and why they together form the scientific method (e.g., it is not just creating a hypothesis that makes something scientific).

• A hypothesis must be testable, meaning there must be some way to collect and analyze data to either support or reject the hypothesis. The best hypothesis is usually the best hypothesis that fits the data today. We recognize that new research or a reevaluation of old research may bring new data, causing the rejection of a well-accepted hypothesis.
• Step 1: Create one or more testable hypotheses to explain observations or answer questions. Without a hypothesis, any experiment is not actually gathering empirical data or evidence; it is simply performing actions to observe.
• Step 2: Test hypothesis (or hypotheses), requiring the collection and analysis of data. If the hypothesis is not tested, then one can have no data to analyze, contributing nothing to the debates at hand.
• Step 3: Accept, modify, or reject hypothesis. If one does not situate the data in reference to its hypothesis, then it was simply performed.
• Step 4: Continually reevaluate hypothesis as new data becomes available and new hypotheses are created. Ensuring that hypotheses are continually reevaluated is a key aspect of science. There is never certainty in science. Scientists always leave room for doubt. By continually retesting and reevaluating hypotheses, science is self-correcting.
• Overall, all steps lead to scientists being able to make and test repeatable experiments and data so that the same conclusion can be independently verified (or refuted).

See pages 61–62 of your text.

5. This answer can vary widely, depending on what human characteristics are chosen to extrapolate from, but it needs to define what the theory means (especially when contrasted with Darwin’s theory).

• This theory assumed that acquired specific traits could be passed on to the offspring of a species (the classic example being a giraffe and its long neck).
• In humans, one could speculate that our species could deviate, depending on one’s occupation and/or environment. For example, people who play professional sports might produce offspring who inherit their fast reaction times or ability to slam dunk a basketball.
• The main point here is understanding which traits are acquired, and which traits are genetic.

See page 66 of your text.

6. The understanding of mutations in this scenario and answer necessarily need to reflect the fact that mutations are not inherently negative, or positive—it depends on the context. Mutations are simply errors in DNA replication. While the word errors sounds bad and errors can result in negative consequences such as disease and deformities, mutations are also responsible for positive variation in all populations.

The answer therefore needs to explain one’s envisioning of the new dog species: Were the mutations spontaneous and beneficial (e.g., a new coloring and stronger legs through genetic drift)? Or were mutations perhaps caused by exposure to radiation or viruses (creating a species of dog that is blind and crippled)? It should also note that species are not formed overnight or through a single interbreeding example and need time over generations to form.

See pages 70–71 of your text.

7. This answer requires one to be able to define the key terms and justify one’s position. There are many traits one could choose to describe how these processes could affect a bear population (claw length, weight and height, coloring, teeth, etc.).

• Genetic drift is a random factor in evolution, occurring when changes in allele frequency come about by chance.
• Gene flow occurs when genes move between populations that are members of the same species but do not normally mate together. Because of separation, new alleles may have formed in one population that may be passed on to others.
• Speciation is the process by which new species emerge. It can happen in numerous ways. Sometimes new species emerge from geographic isolation. Sometimes one entire species evolves into one or more different species. In other cases, however, it is a single population of a species that evolves into another species, coexisting for a time with its ancestral species before the ancestral species become extinct.

See page 71 of your text.

8. This answer should explore what going extinct means, along with an understanding of our involvement in complex processes involving, for example, ecological niches and changes. If possible, one could choose species that have actually gone extinct (e.g., passenger pigeon, the dodo, etc.) and describe how humans were the catalyst for these events. One could also more generally describe the main ways in which humans could make a species go extinct (e.g., overhunting, devastating natural habitats, depleting resources used by another species, etc.).

See pages 74–75 of your text.

9. This answer should recognize the fact that one can believe in both evolution and be religious and explain how such perspectives exist. It should reference and explain nonoverlapping magisteria, and demonstrate knowledge on the subject of science as a framework. However, there is leeway within this question for specifics, and one may choose to also include information on specific beliefs that are incompatible.

See pages 59-60 of your text.

10. This requires the application of the concept of requisite variability (and the consequences of environmental changes) onto a hypothetical situation that could have multiple answers. Thus, requisite variability should be defined, as should extinction.

• Sometimes a species simply does not have the variability within its population to adapt to changing environments (i.e., not enough variability from which nature can choose favorable traits), the variability may be reduced by genetic drift, or the existence of a new species evolving in the regions or coming from elsewhere may outcompete the existing species.
• An asteroid hitting earth caused significant climate change, which the dinosaurs could not effectively adapt to (not having the requisite variability). Small mammals had coexisted with dinosaurs, and many mammals likely became extinct as well. However, with the removal of dinosaurs and changes in environments, some species of small mammals were able to quickly evolve, adapting to changing environments and occupying new ecological niches.
• In the new scenario, dinosaurs would have faced different environmental conditions with a larger population (other species that were more varied would have been less affected). This would have likely meant not only that dinosaurs would have continued evolving (whether through genetic drift or gene flow) but also that the current dominant species today would not have been able to find a stronghold on the ecological niche, as they had done in the scenario that actually occurred in our past.

See page 76 of your text.

1. Genetic drift occurs when

• a) a species becomes extinct and a new species takes over its region.
• b) species rapidly adapt to new ecological niches caused by climate change.
• c) genes move between populations that do not normally mate with one another.
• d) random mutations occur in a population.

2. A hypothetical species becomes extinct when

• a) it is outcompeted by another species for resources in its region.
• b) genetic flow with another species creates a third species.
• c) they need human intervention to continue their existence (e.g., in zoos or rehabilitation centers).
• d) mutations occur in their DNA.

3. Which of the following is an example of speciation?

• a) A large valley has separated a group of bears, eventually leading to two new species of bears.
• b) A species of bears encounters another species of bears; when they interbreed, their offspring are infertile.
• c) A species of bear has developed night vision.
• d) Two species of bears live in the same geographical area that recently experienced significant climate change. One group of bears adapts to the colder temperatures faster and outsurvives the other species.

4. A plant has orange flowers. Its phentotype is therefore

• a) red.
• b) yellow.
• c) orange.
• d) unknown.

5. An empirical finding requires which of the following conditions?

• a) Being hypothesized, experimented upon, and discussed.
• b) Being observed, measured, and analyzed, while also being repeatable.
• c) Being presented in an academic arena (e.g., journal or conference).
• d) Being unique and occurring in natural settings.

6. A scientist is analyzing the results of an experiment that run counter to her hypothesis. She is now reevaluating the hypothesis to begin a new experiment. This is what step in the scientific method?

• a) The second.
• b) The third.
• c) The fourth.
• d) None; what has happened does not align with the scientific method.

7. On his voyages, Darwin noted that finches adapted to their specific contexts; they had, for example, long beaks for poking through bark. Darwin’s eventual theory is thus based on the connection between

• a) skeletal structure and food sources.
• b) homogeneity and speciation.
• c) diversity and environment.
• d) exploration and ecosystems.

8. Complete the following analogy. Finches were to Darwin as what were to Mendel?

• a) Giraffes.
• b) Pea plants.
• c) Maps.
• d) Primates.

9. According to the theory of the Inheritance of Acquired Characteristics, if two smart academics were to produce children, those children would

• a) be very intelligent and know how to conduct excellent research.
• b) not be intelligent, since that trait is canceled out by both parents having it.
• c) constitute a new species.
• d) be more adaptable and able to acquire more efficient use of their resources.

10. Imagine a set of twins who are identical but do not look exactly identical (some traits differ). The study of how factors other than DNA have influenced their occurrence of specific traits is known as

• a) adaptive radiation.
• b) epigenetics.
• c) gradualism.
• d) mutations.

Answers

1. d

Feedback: Genetic drift is a random factor in evolution. The term describes what happens when changes in allele frequency occur by chance.

See page 71.

2. a

Feedback: Extinction means that all members of that species die; sometimes this occurs when the existence of a new species evolving in the regions or coming from elsewhere may outcompete the existing species.

See pages 74-75.

3. a

Feedback: Genetic drift and geographical isolation contribute to this particular example of speciation,i.e., the emergence of a new species.

See pages 73-74.

4. c

Feedback: A genotype is the actual genetic make-up (which is unknown in this scenario), and a phenotype is its physical expression, in this case flowers.

See page 69.

5. b

Feedback: Science is a framework, consisting of principles, methods, and ways of evaluating explanations. It is often described as being empirical, meaning it relies on things that can be observed, measured, and analyzed. It often requires experiments. Results from those experiments must be repeatable by others.

See page 60.

6. c

Feedback: This is an example of how the fourth and final step occurs: reevaluating a hypothesis when new data becomes available.

See pages 61-62.

7. c

Feedback: The diversity he witnessed was a result of mutations suited to particular environments.

See pages 66-67.

8. b

Feedback: Just as Darwin’s scientific findings relied on insights based on observations of finches in the Galapagos, Mendel’s findings relied on breeding pea plants.

See page 68.

9. a

Feedback: Lamarck proposed that an individual who acquired specific traits could pass those traits on to its offspring.

See page 66.

10. b

Feedback: We realize that genes are the primary way traits are inherited, but that other factors, such as chemical reactions, may also have a role. Epigenetics essentially refers to the study of how factors other than DNA or genes may influence the occurrence of specific traits.

See page 75.