The Tangle of Natural Purposes That Is Us
Darwin thought that many traits of organisms that appear to have been purposefully designed can instead be accounted for by natural selection. Human eyes are exquisitely engineered for extracting information from surrounding light. It certainly appears as though this had been the aim of their design. Darwin claimed, however, that this wonderful design did not result from any purpose or aim. Rather, during the evolution of humans, whenever one design performed better than another, that design tended to be preserved in future generations. Further improvements were accidentally thrown up (by genetic mutation, according to modern biology) then retained in turn, leading fi nally to the current design. And so for other superbly adaptive features of our design including some of our behavioral dispositions, for example, the protective eye blink refl ex. Indeed, spectacular design for current function is considered by biologists to be the very strongest evidence for the operation of natural selection-rather than, say, pleiotropy, genetic drift, exaptation, allometry, or an accidental by-product of design for some other purpose-in the evolution of a trait.