Steven Pinker -- How the Mind Works - Hampshire High Italian ...

Revenge of the Nerds 169tant, but the differences are important, too! Developmental constraintsonly rule out broad classes of options. They cannot, by themselves, forcea functioning organ to come into being. An embryological constraint like"Thou shalt grow wings" is an absurdity. The vast majority of hunks ofanimal flesh do not meet the stringent engineering demands of poweredflight, so it is infinitesimally unlikely that the creeping and bumping cellsin the microscopic layers of the developing embryo are obliged to alignthemselves into bones, skin, muscles, and feathers with just the rightarchitecture to get the bird aloft—unless, of course, the developmentalprogram had been shaped to bring about that outcome by the history ofsuccesses and failures of the whole body.Natural selection should not be pitted against developmental, genetic,or phylogenetic constraints, as if the more important one of them is, theless important the others are. Selection versus constraints is a phonydichotomy, as crippling to clear thinking as the dichotomy betweeninnateness and learning. Selection can only select from alternatives thatare growable as carbon-based living stuff, but in the absence of selectionthat stuff could just as easily grow into scar tissue, scum, tumors, warts,tissue cultures, and quivering amorphous protoplasm as into functioningorgans. Thus selection and constraints are both important but are answersto different questions. The question "Why does this creature have suchand-suchan organ:*" by itself is meaningless. It can only be asked whenfollowed by a compared-to-what phrase. Why do birds have wings (asopposed to propellers)? Because you can't grow a vertebrate with propellers.Why do birds have wings (as opposed to forelegs or hands orstumps)? Because selection favored ancestors of birds that could fly.Another widespread misconception is that if an organ changed itsfunction in the course of evolution, it did not evolve by natural selection.One discovery has been cited over and over in support of the misconception:the wings of insects were not originally used for locomotion. Like afriend-of-a-friend legend, that discovery has mutated in the retelling:wings evolved for something else but happened to be perfectly adaptedfor flight, and one day the insects just decided to fly with them; the evolutionof insect wings refutes Darwin because they would have had toevolve gradually and half a wing is useless; the wings of birds were notoriginally used for locomotion (probably a misremembering of anotherfact, that the first feathers evolved not for flight but for insulation). Allone has to do is say "the evolution of wings" and audiences will nodknowingly, completing the anti-adaptationist argument for themselves.