In present-day life forms, major parts and behaviors virtually always serve significant biological functions. Recently, such functions have been demonstrated even for the appendix and tonsils, traditionally regarded as merely vestigial. Meanwhile, nonfunctional parts and processes must always be of relatively minor significance. For instance, modern humans develop goose bumps when exposed to cold. This phenomenon, caused by contractions of tiny muscles in the skin, is believed to be a vestige of an earlier evolutionary stage, when the ancestors of humans possessed well-developed fur. For those ancestors, the contractions caused the hairs to stand on end, thus conserving heat.* Today, of course, we no longer possess fur, and goose bumps serve no apparent survival end. The phenomenon endures only because the energy cost and survival disadvantage it imposes on the organism is of marginal consequence. (Such phenomena raise an apparently insurmountable problem for those who reject evolutionary theory.)

Similarly, it has been observed that the most stable parts of the DNA strands—that is, those least susceptible to mutation—are those portions that are most crucial to the establishment of a viable organism. Thus the functional requirements of life tend to limit even the kinds and degree of accidental changes to life itself.     
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    *Frederick S. Hulse, The Human Species: An Introduction to Physical Anthropology (New York: Random House, 1963), p. 76.

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