"Most human beings now obtain a large share of the provision for their daily lives from others to whom they are not related by blood or marriage. Even in poor rural societies people depend significantly on nonrelatives for food, clothing, medicine, protection, and shelter. In cities, most of these nonrelatives crucial to our survival are complete strangers. Nature knows no other examples of such complex mutual dependence among strangers. A division of labor occurs, it is true, in some other species, such as the social insects, but chiefly among close relatives—the workers in a beehive or an ant colony are sisters. There are some cases of apparent cooperation between colonies of ants founded by unrelated queens, though the explanation of this phenomenon remains controversial….
"No solution to this puzzle can be found in evolutionary biology alone. Ten thousand years is too short a time for the genetic makeup of Homo sapiens sapiens to have adapted comprehensively to its new social surroundings. If it were somehow possible to assemble together all your direct same-sex ancestors—your father and your father’s father and so on if you’re male, your mother and your mother’s mother and so on if you’re female; one for each generation right back to the dawn of agriculture—you and all of these individuals could fit comfortably in a medium-sized lecture hall. Only half of you would have known the wheel, and only 1 per cent of you the motor car….
"Yet evolutionary biology has something important to tell us all the same. For the division of labor among human beings has had to piggyback on a physiology and a psychology that evolved to meet a far different set of ecological problems. These were problems faced by hunter-gatherers, mainly on the African woodland savannah, over the six or seven million years that separate us from our last common ancestor with chimpanzees and bonobos. Some time in the last two hundred thousand years or so—less than one-thirtieth of that total span—a series of changes, minuscule to geneticists, vast in the space of cultural potential, occurred to make human beings capable of abstract, symbolic thought and communication.
"Just when they occurred involves difficult issues of dating, but since all human beings share these capacities the genetic changes that made them happen probably occurred at least 140,000 years ago. But the first evidence of the new cultural capabilities to which they gave rise is found in the cave paintings, grave goods, and other symbolic artifacts left by hunter-gatherer communities of anatomically modern man (Cro-Magnon man, as he is sometimes known), which are no older than sixty or seventy thousand years—and most are much younger. These capabilities seem to have made a move toward agriculture and settlement possible once the environmental conditions became favorable, after the end of the last ice age.
"Indeed, the fact that agriculture was independently invented at least seven times, at close intervals, in different parts of the world suggests it was more than possible; it may even have been in some way inevitable. These capabilities also enabled human beings to construct the social rules and habits that would constrain their own violent and unreliable instincts enough to make society possible on a larger, more formal scale. And they laid the foundation for the accumulation of knowledge that would provide humanity as a whole with a reservoir of shared skills vastly greater than the skills available to any single person. But these cultural capabilities did not evolve because of their value in making the modern division of labor possible. Quite the contrary: modern society is an opportunistic experiment…"
--Paul Seabright, The Company of Strangers