Chapter 1: Adaptation by Natural Selection

Chapter Outline

1. What Is Adaptation?

1. Components of an organism that help it survive and reproduce.
2. The human eye is an example of a complex adaptation.
3. Before Darwin, adaptation was explained as the work of a heavenly designer.

2. Darwin's Theory of Adaptation

1. After medical school, Darwin spent time on the H.M.S. Beagle charting the coast of South America and studying the flora and fauna there.
2. Darwin returned to London and developed three postulates of adaptation:
• Population increases infinitely, but the environment is finite.
• Organisms vary, and variation affects survival.
• Variation is heritable.
3. Galápagos finches
• Peter and Rosemary Grant of Princeton University studied the finches for years.
• Drought struck Daphne Major in the late 1970s, and plant life dwindled.
• Large, hard seeds and beak-size variation contributed to adaptation.
• Finches with deeper beaks survived in larger numbers than those with smaller beaks (Fig. 1.9).
• Beak depth was passed on to new generations (Fig. 1.10), causing a 4% increase in average beak depth in the finch population.
• The Grants’s long-term research shows stabilizing selection and equilibrium in beak size (Fig 1.13).
4. Individual versus species
• Darwin put forward that a species is dynamic—a population made up of individuals.
• Selection creates adaptations that are beneficial to the individual, not necessarily to the population or species.

3. What Are Complex Adaptations?

1. Continuous variation is important for complex adaptations.
2. Complex adaptations are the result of small, random variations.
3. Complex adaptations require all intermediate steps to be useful.
• Example: Human eye (Fig. 1.15)
4. Convergent evolution occurs when a similar adaptation occurs in unrelated groups of animals.
• Examples: Eyes, marsupials

4. How Fast Does Evolution Occur?

1. Change can occur rapidly. Examples include:
• Beak morphology of Galápagos finches
• Body size of Jersey elk
• Dog breeds
• Eye
2. Nilsson and Pelger of Lund University simulated the evolution of the eye in fish and found that this complex structure could evolve in less than a million years.

5. Problems Darwin Could Not Solve

1. Blending inheritance would eliminate variation by making each individual the average of its parents.
2. Natural selection would also eliminate variation by removing variants from populations.
3. How can new traits be introduced to a population?

In This Chapter

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