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The Chapter in Review
Darwin's Theory of Evolution

Charles Darwin took a position as a naturalist aboard the HMS Beagle and made a trip around the world, largely in the Southern Hemisphere.

Before Darwin

Before Darwin, people believed that Earth was young, species did not change, variations were imperfections, and observations could substantiate these views.

  • Cuvier was an early paleontologist who believed that species do not change. He observed species come and go in the fossil record, and he said these changes were due to catastrophies.

  • Lamarck was a zoologist who hypothesized that evolution and adaptation to the environment do occur. He suggested that acquired characteristics could be inherited. For example, he said giraffes stretched their necks to reach food in trees, and then this change was inherited by the next generation.

Darwin's Conclusions

Darwin's conclusions based on geology and fossils are:

  • The Earth is very old, giving time for evolution to occur.

  • Living things are descended from extinct forms known only from the fossil record.

Darwin's conclusions based on biogeography are:

  • Living things evolve where they are. This explains, for example, why South America has the Patagonian hare, whereas England has the rabbit.

  • Living things are adapted to local environments. This explains why there are many types of finches and tortoises in the Galápagos Islands.

Natural Selection and Adaptation

According to Darwin, the result of natural selection is a population better adapted to its local environment than previous generations:

Darwin and Wallace

Alfred Russel Wallace was a naturalist who, like Darwin, traveled to other continents in the Southern Hemisphere. He also collected evidence of common descent, and his reading of Malthus caused him to develop the same mechanism for adaptation (natural selection) as Darwin. Darwin's work was more thorough, as evidenced by his book On the Origin of Species.

Evidence for Evolution

A theory in science is a concept supported by much evidence, and the theory of evolution is supported by several types of evidence:

  • The fossil record indicates the history of life in general and allows us to trace the descent of a particular group.

  • Biogeography shows that the distribution of organisms on Earth is explainable by assuming organisms evolved in one locale.

  • Anatomy and development of organisms reveals homologies explainable only by common ancestry.

  • Biochemical molecules of the same type occur in all organisms. Differences indicate the degree of relatedness.

Key Terms
Testing Yourself

Choose the best answer for each question.

  1. developed the idea that acquired characteristics can be inherited.

    1. Darwin

    2. Lamarck

    3. Wallace

    4. Sedgwick

    5. Cuvier

  2. The major feature Darwin noticed that differed among species of Galápagos finches was

    1. coloration.

    2. beak size.

    3. beak color.

    4. length of tail feathers.

  3. Which of the following is not an example of natural selection?

    1. Insect populations exposed to pesticides become resistant to the chemicals.

    2. Plant species that produce fragrances to attract pollinators produce more offspring.

    3. Rabbits that sprint quickly are more likely to escape predation.

    4. On a tree, leaves that grow in the shade are larger than those that grow in the sun.

  4. The variations necessary for natural selection

    1. occur randomly.

    2. are influenced by environment.

    3. can be caused by mutation.

    4. can be caused by recombination during meiosis.

    5. All of these are correct.

  5. Which is most likely to be favored during natural selection, but not artificial selection?

    1. fast seed germination rate

    2. short generation time

    3. efficient seed dispersal

    4. lean pork meat production

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  7. Natural selection is the only process that results in

    1. genetic variation.

    2. adaptation to the environment.

    3. phenotypic change.

    4. competition among individuals in a population.

  8. Why was it helpful to Darwin to learn that Lyell concluded the Earth was very old?

    1. An old Earth has more fossils than a new Earth.

    2. It meant there was enough time for evolution to have occurred slowly.

    3. There was enough time for the same species to spread out into all continents.

    4. Darwin said artificial selection occurs slowly.

    5. All of these are correct.

  9. In the following diagram, contrast Lamarck's proposal with Darwin's proposal by matching the phrases in the key to the letters in the diagram.


Originally, giraffe neck length varied.

Giraffes stretched their necks in order to reach food.

Struggle to exist causes long-necked giraffes to have the most offspring.

Originally, giraffes had short necks.

Today most giraffes have long necks. (used twice)

  1. All the finches on the Galápagos Islands

    1. are unrelated but descended from a common ancestor.

    2. are descended from a common ancestor, and therefore related.

    3. rarely compete for the same food source.

    4. Both a and c are correct.

    5. Both b and c are correct.

  2. Evolution is considered a

    1. hypothesis because it is supported by data from the fossil record.

    2. hypothesis because it is supported by multiple types of data.

    3. theory because it is supported by data from the fossil record.

    4. theory because it is supported by multiple types of data.

  3. Catastrophists were not able to explain

    1. multiple extinctions.

    2. the replacement of one group of organisms by another.

    3. successive changes that link groups of organisms in the fossil record.

    4. More than one of these are correct.

For questions 12–15, match the description with the type of evidence for evolution it supports, as listed in the key. Answers can be used more than once.

  1. biogeographical

  2. anatomical

  3. biochemical

  1. The genetic code is the same for all organisms.

  2. The human knee bone and spine were derived from ancestral structures that supported four-legged animals.

  3. The South American continent lacks rabbits even though the environment is quite suitable.

  4. The amino acid sequence of human hemoglobin is more similar to that of rhesus monkeys than to that of mice.

  5. Fossils that serve as transitional links allow scientists to

    1. determine how prehistoric animals interacted with each other.

    2. deduce the order in which various groups of animals arose.

    3. relate climate change to evolutionary trends.

    4. determine why evolutionary changes occur.

  6. Among vertebrates, the flipper of a dolphin and the fin of a tuna are

    1. homologous structures.

    2. homogeneous structures.

    3. analogous structures.

    4. reciprocal structures.

  7. Which of these pairs is mismatched?

    1. Charles Darwin—natural selection

    2. Cuvier—series of catastrophes explains the fossil record

    3. Lamarck—uniformitarianism

    4. All of these are correct.

  8. According to the inheritance of acquired characteristics hypothesis,

    1. if a man loses his hand, then his children will also be missing a hand.

    2. changes in phenotype are passed on by way of the genotype to the next generation.

    3. organisms are able to bring about a change in their phenotype.

    4. evolution is striving toward particular traits.

    5. All of these are correct.

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  10. Organisms

    1. compete with other members of their species.

    2. differ in fitness.

    3. are adapted to their environment.

    4. are related by descent from common ancestors.

    5. All of these are correct.

  11. DNA nucleotide differences between organisms

    1. indicate how closely related organisms are.

    2. indicate that evolution occurs.

    3. explain why there are phenotypic differences.

    4. are to be expected.

    5. All of these are correct.

  12. The fossil record offers direct evidence for common descent because you can

    1. see that the types of fossils change over time.

    2. sometimes find common ancestors.

    3. trace the ancestry of a particular group.

    4. trace the biological history of living things.

    5. All of these are correct.

  13. Molecular evidence is increasingly used today to establish relationships because

    1. genes are composed of DNA.

    2. the more similar the genes, the more likely two organisms are related.

    3. this evidence is objective and not subject to opinion.

    4. All of these are correct.

  14. For there to be homologous structures,

    1. a common ancestor had to have existed.

    2. analogous structures also have to exist.

    3. the bones have to be used similarly.

    4. All of these are correct.

Thinking Scientifically
  1. The human appendix, a vestigial extension off the large intestine, is homologous to a structure called a caecum in other mammals. A caecum, generally larger than our appendix, houses bacteria that aid in digesting cellulose, the main component of plants. How might the presence of the appendix be used to show our common ancestry with other mammals, and what might it tell us about the dietary history of humans?

  2. Geneticists compare DNA base sequences among organisms and from this data determine a gene's rate of evolution. Different genes have been found to evolve at different rates. Explain why some genes might have faster rates of evolution than other genes as populations adapt to their environments.

  3. Both Darwin and Wallace concluded that natural selection is the mechanism for biological evolution while observing life on islands. The Hawaiian and nearby islands once had at least 50 species of honeycreepers and these occurred nowhere else on Earth. Natural selection occurs everywhere and in all species. What characteristics of islands allow the outcome of natural selection to be so obvious?

Essentials of Biology Website

The companion website for Essentials of Biology provides a wealth of information organized and integrated by chapter. You will find practice tests, animations, videos, and much more that will complement your learning and understanding of general biology.