Everyday, science seems to chip away at our autonomy. When researchers aren't uncovering physical differences in the way men and women use their brains, they're asserting genetic influences on intelligence, sexual orientation, obesity or alcoholism. Or they're suggesting that the level of some brain chemical affects one's chances of committing violent crimes. Each new finding leaves the impression that nature is winning out over nurture—that biology is destiny and free will an illusion. But the nature-nurture dichotomy is itself an illusion. As many scholars are now realizing, everything we associate with 'nurture' is at some level a product of our biology—and every aspect of our biology, from brain development to food preference, has been shaped by an environment. Asking whether nature or nurture is more important is like asking whether length or width is a better gauge of size. Darwin recognized more than 100 years ago that Homo sapiens evolved by the same process as every other species on earth. And philosophers such as William James were eager to apply Darwin's insights to human psychology. But during the first part of this century, the rise of 'social Darwinism' (a non-Darwinian, sink-or-swim political philosophy) and late Nazi eugenics spawned a deep suspicion of biologically inspired social science. By 1954, anthropologist Ashley Montagu was declaring that mankind has 'no instincts because everything he is and has becomes what she has learned, acquired, from his culture.' The distinction between innate and acquired seems razor sharp, until you try slicing life with it. Consider the development of the brain. While gestating in the womb, a child develops some 50 trillion neurons. But those cells become functional only as they respond to outside stimuli. During the first year of life, the most frequently stimulated neurons form. elaborate networks for processing information, while the others wither and die. You could say that our brains determine the structure of our brains. Social behavior. follows the same principle. From the old nature-versus-nurture perspective, a tendency that isn't uniformly expressed in every part of the world must be 'cultural' rather than 'natural'. But there is no reason to assume that a universal impulse would always find the same expression. As the evolutionists John Tooby and Leda Cosmildes have observed, biology can't dictate what language a child will speak, what games she'll feel guilty or jealous about. But it virtually guarantees that she'll do all of those things, whether she grows up in New Jersey or New Guinea. Biology, in short, doesn't determine exactly what we' Il do in life. It determines how different environments will affect us. And our biology is itself a record of the environments our ancestors encountered. Consider the sexes' different perceptual styles. Men tend to excel at spatial reasoning, women at spotting stationary objects and remembering their locations. Such discrepancies may have a biological basis, but researchers have traced the biology back to specific environmental pressures. Archeological findings suggest that men hunted, and women foraged, throughout vast stretches of revolutionary time. And psychologists Irwin Silverman and Marion Eals have noted that 'tracking and killing animals entail different kinds of spatial problems than does foraging for edible plants.' It can be inferred from the passage that what Montagu emphasized in his explanation is ______ .