The evolution of organisms is a change in traits that occurs over a long period of time. Let us understand the theory of natural selection systematized by Darwin and its evidence.
Basic Knowledge
Evidence for evolution: ① Fossil record (changes in the ages of strata and biota; transitional fossil = Archaeopteryx, intermediate between reptiles and birds). ② Comparative anatomy: homologous organs (same origin, different form: a bird's wing and a human arm) and vestigial organs (homologous organs that have lost their function: the human coccyx). Analogous organs (different origin, similar form: a bird's wing and an insect's wing) are evidence of convergent evolution. ③ Embryological evidence (similarity in early developmental forms). ④ Molecular biological evidence (DNA sequences are more similar in more closely related species).
Darwin's theory of natural selection (1859): ① Variation (genetic variation exists among individuals) → ② Overproduction (more offspring are born than can survive) → ③ Struggle for existence → ④ Natural selection (individuals with suitable traits survive and reproduce in greater numbers) → ⑤ Heredity (selected traits are passed to offspring, changing the population).
Modern synthesis (neo-Darwinism): Integrates natural selection, Mendelian genetics, and population genetics. Mutation and recombination are sources of variation.
Explain the diversification of finches in the Galápagos Islands using the four elements of natural selection.
Answer: ① Variation: There were individual differences in the shape and size of beaks within the ancestral finch population. ② Struggle for existence: There were more individuals than the amount of food available on each island. ③ Natural selection: Individuals with beak shapes suited to each island's food sources (seeds, insects, cacti, and so on) had an advantage in survival and reproduction. ④ Heredity: Suitable beak traits were passed to offspring, and the finches diverged into species adapted to the environment of each island.
- Evidence for evolution = fossils, homologous organs, embryology, and molecular biology
- Homologous organs = same origin, different form (a bird's wing and a human arm)
- Analogous organs = different origin, similar form (evidence of convergent evolution)
- Vestigial organs = homologous organs that have lost their function (the human coccyx)
- Darwin = variation, overproduction, struggle for existence, natural selection, and heredity
- Archaeopteryx = transitional fossil between reptiles and birds
- Modern synthesis = natural selection + Mendelian genetics + population genetics
Points to Note
① Do not confuse homologous organs (same origin, different form) with analogous organs (different origin, similar form). ② Natural selection is not teleological. ③ The inheritance of acquired characteristics in the theory of use and disuse (Lamarck) has been rejected, and the theory of natural selection is accepted.
Practice
- Give one example of homologous organs and explain why it is evidence for evolution.
- State Darwin's five steps of natural selection in order.
- Between what kinds of organisms is Archaeopteryx considered an intermediate form?