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Two Supposed Examples of Darwinian Evolution
Looking for proof of evolution? Biology textbooks frequently cite two examples to show that Darwinian evolution can take place in the real world.The first commonly offered example involves a species of moths in 19th-century England. The species had two varieties, one light- and the other dark-colored. For years the lighter variety predominated, since its coloration more closely matched the bark of trees on which it rested.
However, as soot from many factories gradually darkened the tree bark, the lighter moths stood out against the now-darkened tree trunks. Birds could see the light moths better and soon devoured most. Before long the darker moths, being better camouflaged against the darker bark, became the more common variety. "In fact this is the first direct evidence actually obtained," says a biology textbook, "to support Darwin's theory that natural selection occurs" (Contemporary Biology, 1973, p. 567). Convincing evidence-or is it?
This actually might have been a case of Darwinian natural selection changing the species to confer a survival advantage-if the light moths had turned into dark ones. But no such thing happened. In fact, both types were already in existence. The lighter moths didn't evolve into darker moths. They were eaten. The proportion of dark moths increased while the light moths decreased.
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