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

170 J HOW THE MIND WORKSHow can anyone say that any organ was selected for its current function?Maybe it evolved for something else and the animal is only using it forthat function now, like the nose holding up spectacles and all that stuffabout insect wings that everyone knows about (or was it bird wings?).Here is what you find when you check the facts. Many organs that wesee today have maintained their original function. The eye was always aneye, from light-sensitive spot to image-focusing eyeball. Others changedtheir function. That is not a new discovery. Darwin gave many examples,such as the pectoral fins of fishes becoming the forelimbs of horses, theflippers of whales, the wings of birds, the digging claws of moles, and thearms of humans. In Darwin's day the similarities were powerful evidencefor the fact of evolution, and they still are. Darwin also cited changes infunction to explain the problem of "the incipient stages of useful structures,"perennially popular among creationists. How could a complexorgan gradually evolve when only the final form is usable? Most often thepremise of unusability is just wrong. For example, partial eyes have partialsight, which is better than no sight at all. But sometimes the answer isthat before an organ was selected to assume its current form, it wasadapted for something else and then went through an intermediate stagein which it accomplished both. The delicate chain of middle-ear bones inmammals (hammer, anvil, stirrup) began as parts of the jaw hinge of reptiles.Reptiles often sense vibrations by lowering their jaws to the ground.Certain bones served both as jaw hinges and as vibration transmitters.That set the stage for the bones to specialize more and more as soundtransmitters, causing them to shrink and move into their current shapeand role. Darwin called the earlier forms "pre-adaptations," though hestressed that evolution does not somehow anticipate next year's model.There is nothing mysterious about the evolution of birds' wings. Halfa wing will not let you soar like an eagle, but it will let you glide or parachutefrom trees (as many living animals do), and it will let you leap ortake off in bursts while running, like a chicken trying to escape a farmer.Paleontologists disagree about which intermediate stage is best supportedby the fossil and aerodynamic evidence, but there is nothing hereto give comfort to a creationist or a social scientist.The theory of the evolution of insect wings proposed by Joel Kingsolverand Mimi Koehl, far from being a refutation of adaptationism, isone of its finest moments. Small cold-blooded animals like insects struggleto regulate their temperature. Their high ratio of surface area to volumemakes them heat up and cool down quickly. (That is why there are