First, environment, though it determines nothing, influences everything – shaping lives the way wind shapes a tree. Humans occupy a vastly bigger environmental range than any comparable animal. Other great apes – and we should never forget that we are just well adapted apes – inhabit continuous or contiguous niches. Apart from some extinct hominids, we are the only apes to have spread over almost the entire land surface of the globe. Every shift to new physical surroundings demanded adaptations in our ancestors’ ways of life, opening chasms of culture across physical boundaries.
Second, psychic qualities matter. Humans moved out of their East African environment of origin because they were exceptionally imaginative animals, capable of envisioning life in an unexperienced world. Imagination or, more simply, the power of seeing something that isn’t there, is what biologists call a “spandrel”: an unevolved consequence of our ancestors’ evolved power of anticipation – the power of seeing what is not yet there – which our ancestors needed to make up for their physical deficiencies in competition with stronger, faster, more agile animals with better teeth, talons, jaws and digestions. Our bad memories helped. Humans who congratulate themselves on their supposedly superior memories are wrong: in quantifiable ways, chimps and gorillas outperform students in some kinds of memory-test. The unreliability of witnesses proves our shortcomings. If anticipation is seeing what’s not yet there, memory is the ability to see what’s there no longer. Both overlap with and contribute to imagination. Every false memory is an innovation added to experience.
Finally, divergence is not the whole story. At intervals in history, human groups have re-established contact, exchanged culture and, at least in some respects, grown more like each other. So convergence threads into the story of divergence. Cultural contagion accelerated about half a millennium ago, reaching across the globe, as explorers, colonizers, conquerors, merchants and missionaries crossed previously unnavigated oceans and united formerly sundered civilisations. We are now in a peculiarly intense phase of convergence, which we usually call globalization: all over the world, people want to adopt the same politics and economics, wear the same dress, eat the same food, buy the same art, listen to the same music, even talk the same language….
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