Theory of Evolution

Essential Content

A. Evidence for The Theory of Evolution

1. Fossil Record

2. Comparative Anatomy

3. Comparative Embryology

4. Biogeography

5. Molecular Biology (Genetic Code)

6. Observed Evolutionary Change

B. Evolution through Natural Selection

1. Contributions to the development of a theory

a. Geologic Change

b. Overpopulation

c. Availability of Resources

d. Acquired Traits

C. Darwin’s Natural Selection

1. Darwin’s Observations

a. Variation of Traits on Galapagos Islands

b. Adaptations Within Species

2. Natural Selection

a. Inherited Variation

b. Differential Reproductive Success

c. Survival of the fittest

3. Speciation

Objectives

• Evaluate and explain the multiple bodies of evidence that support the scientific theory of evolution.

• Identify and describe anatomical similarities such as homologous and analogous structures and vestigial organs when referring to comparative anatomy and comparative embryology.

• Predict ancestry of certain organisms based on homologous or vestigial

• Evaluate the contributions of scientists such as Darwin, Lamarck, Lyell, Malthus, and Wallace aided in the development of the scientific theory of evolution.

• Describe conditions requires for natural selection including (tenets of Darwin) overproduction of offspring, inherited variation, and struggle to survive, which results on differential reproductive success.

• Explain how natural selection affects different types of traits in a species.

Vocabulary

evolution, natural selection, fossil record, comparative anatomy, homologous structure, analogous structure, vestigial structure, comparative embryology, biogeography, molecular biology, extinction, fitness, adaptations, mutation, variation, common ancestor

Evolution by Natural Selection

Darwin proposed a mechanism for evolution: natural selection.

This mechanism was elegant and logical, and it explained how populations could evolve (undergo descent with modification) in such a way that they became better suited to their environments over time.

Darwin's concept of natural selection was based on several key observations:

• Traits are often heritable. In living organisms, many characteristics are inherited, or passed from parent to offspring. (Darwin knew this was the case, even though he did not know that traits were inherited via genes.)

• More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.

• Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits (color, size, shape, etc.), and many of these features will be heritable.

Based on these simple observations, Darwin concluded the following:

• In a population, some individuals will have inherited traits that help them survive and reproduce (given the conditions of the environment, such as the predators and food sources present). The individuals with the helpful traits will leave more offspring in the next generation than their peers, since the traits make them more effective at surviving and reproducing.

• Because the helpful traits are heritable, and because organisms with these traits leave more offspring, the traits will tend to become more common (present in a larger fraction of the population) in the next generation.

• Over generations, the population will become adapted to its environment (as individuals with traits helpful in that environment have consistently greater reproductive success than their peers).