Evolution, Organic

Evidence for Evolution

Matt Ridley points out that two fundamental questions need to be answered to demonstrate evolution. Do populations and species change through time? And do living organisms share a common ancestor? The evidence used to answer these questions in the affirmative comes from a number of sources, including observation of evolution on a small scale, the presence of extensive variation among populations and subspecies, homology, adaptive radiation, and the fossil record.

Evolution “on a small scale,” over a number of generations rather than over millions of years, has been achieved under domestic and experimental conditions and observed in the wild. The origin and development of domestic breeds of animals and plants has been a topic of interest to anthropologists and clearly demonstrates that species change. In On the Origin of Species (1859), Charles Darwin discusses the production of domestic breeds as the result of “accumulative selection” by humans and points out that breeders and horticulturalists intentionally modify breeds within a human lifetime. He particularly concentrates on the origin of pigeon breeds. Darwin also addresses “unconscious selection,” in which a breed is altered simply by breeding the “best” individuals (for example, the English pointer dog). In both techniques, the breeder is allowing only those individuals with extreme values of a particular character to produce offspring during each consecutive generation (the “traditional breeder's approach”). This shifts the mean value for the selected characteristic during successive generations in the descendants: The breeder is applying directional selection to the particular trait of interest (the somewhat unfortunate term “artificial selection” is often applied to this methodology, which could be misconstrued). Darwin expands upon this discussion in The Variation of Animals and Plants Under Domestication (1883) and states that domestication is a gigantic experiment in selection. Modern [Page 899]discussions of the principles and results of plant and animal breeding are couched in terms of genetics.

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