22.1 Evidence indicates that natural selection can produce evolutionary change.
The Beaks of Darwin's Finches
• Darwin collected 31 finch specimens from three Galápagos Islands. (p. 454)
• Darwin found correspondence between 14 finch species and their food sources (p. 454)
• Observations suggest that beak differences evolved as adaptations to different food sources. (p. 455)
Peppered Moths and Industrial Melanism
• Adults range in color from light gray to black (dominant). (p. 456)
• Black moths were rare before 1850, but common after that. (p. 456)
• The Industrial Revolution caused trees to become sooty, making light-colored moths more visible to predators. Thus, darker moths became more prevalent than lighter moths. (p. 456)
• The second half of the twentieth century saw widespread pollution control, and subsequently a reversed trend away from melanism. (p. 457)
• No matter the agent or the selective force, selection favored dark moths in polluted habitats and light moths in pristine areas. (p. 457)
Artificial Selection
• Artificial selection has produced substantial change in almost every case to which it has been applied. (p. 458)
• Selection for a trait in a lab animal such as the fruit fly leads to strong and predictable evolutionary response. (p. 458)
• Differences in agricultural crops and the domestication of animals have resulted from generations of selection for desirable traits. (pp. 458-459)
• By extrapolation, selection, over the course of many millions of years, likely has the power to produce the current diversity of life. (p. 459)
22.2 Fossil evidence indicates that evolution has occurred.
The Fossil Record
• Rock fossils are created when an organism becomes buried in sediments, and hard tissue mineralizes. (p. 460)
• Fossils can be dated in a relative manner by looking at their relative position in rock strata, and dated in an absolute manner using radioactive isotopes and the ratio of derivative isotopes. (p. 460).
• At its largest scale, the fossil record documents the course of life through time. (p. 460)
• Demonstration of successive change is one of the strongest lines of evolutionary evidence. (p. 461)
The Evolution of Horses
• The evolution of horses is one of the best-studied cases in the fossil record. (p. 462)
• The earliest horses were small, with short legs and broad feet. (p. 462)
• Most changes to horses have been explained as adaptations to changing global climates. (p. 463)
• Modern horse diversity is relatively limited. (p. 463)
22.3 Evidence for evolution can be found in other fields of biology.
The Anatomical Record
• Homologous structures have different appearances and functions but are derived from the same body part in a common ancestor. (p. 464)
• Relict developmental forms in a wide variety of vertebrate embryos suggest that evolution has modified ancestral developmental patterns. (p. 464)
• Vestigial structures have no apparent function, but resemble structures of presumed ancestors. (p. 465)
The Molecular Record
• Recent descendants from a common ancestor initially exhibit relatively high DNA similarity. (p. 466)
• The more distantly related two organisms are, the larger the number of DNA differences, in both coding and noncoding regions, that evolve. (p. 466)
Convergent Evolution and the Biogeographical Record
• Different areas can exhibit groups of organisms that resemble one another. (p. 467)
• Natural selection appears to have favored parallel evolutionary adaptations within similar environments.
• Island forms are often closely related to species on the nearest mainland. (p. 467)
22.4 The theory of evolution has proven controversial.
Darwin's Critics
• Darwin's critics raise several objections to teaching evolution: evolution is not solidly demonstrated; there is a lack of fossil intermediates; the intelligent design argument; evolution violates the Second Law of Thermodynamics; proteins are too improbable; natural selection does not imply evolution; and the irreducible complexity argument. None of these objections has scientific merit. (p. 468)