Natural Selection

The process by which heritable traits that improve an organism's odds of surviving and reproducing in a given environment become more common in a population over successive generations, first described by Charles Darwin and Alfred Russel Wallace in 1858. Natural selection requires only that individuals vary, that some of that variation is heritable, and that it affects reproductive success; it does not require conscious intent, and it acts on existing variation rather than producing new traits on demand. The monarch butterfly's bright orange and black warning coloration is a well-documented product of natural selection: caterpillars sequester toxic compounds from the milkweed they eat, carry the toxin into adulthood, and the conspicuous pattern advertises that toxicity to predators, a defense so effective that the unrelated, non-toxic viceroy butterfly has independently evolved a strikingly similar pattern of its own, a form of mimicry that only makes evolutionary sense as a product of selection.