The Invention of Childhood, or Why It Hurts to Have a Baby [Excerpt] - 0 views
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It’s impossible to overstate the colossal impact this turn of events had on our evolution, but it requires some context to fully appreciate what it means. Our habit of being born early is part of a larger, stranger phenomenon that scientists call neoteny, a term that covers a lot of evolutionary sins at the same time it explains so much of what makes us the unique, even bizarre creatures we are.
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you might think that neoteny is simply a matter of a species holding on to as many youthful traits of an ancestor as long into adulthood as possible
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And our brain development is anything but arrested. In fact, just the opposite. As I said, complicated.
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The different ways some parts of us seem to accelerate and mature while others bide their time or halt altogether has generated a flock of terms related to neoteny—paedomorphosis, heterochrony, progenesis, hypermorphosis, and recapitulation.
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In the end, however, it comes down to this—each represents an evolution of evolution itself, an exceptional and rare combination of adaptations that changed our ancestors so fundamentally that it led to an ape (us) capable of changing the very planet that brought it into existence.5 Put another way, it changed everything.
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Mostly we think of Darwin’s “descent by natural selection” as a chance transformation of newly arrived mutations—usually physical—into an asset rather than a liability, which is then passed along to the next generation.
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But what neoteny (and paedomorphosis and all the rest) illustrate is that the forces of evolution don’t simply play with physical attributes, they play with time, too, or more accurately they can shift the times when genes are expressed and hormones flow, which not only alters looks but behavior, with fascinating results.
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By being born “early,” our youth is amplified and elongated, and it continues to stretch out across our lives into the extended childhood that makes us so different from the other primates that preceded us.
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All of the evidence emphatically points to our direct, gracile ape ancestors steadily extending their youth. They were inventing childhood.
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Exactly how all of this unfolded on the wild and sprawling plains of Africa isn’t clear precisely, but there can be no doubt that it did. We stand as the indisputable proof.
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The clustered neurons that together compose the brains of all primates grow at a rate before birth that even the most objective laboratory researcher could only call exuberant, maybe even scary.
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But for most species that growth slows markedly after birth. The brain of a monkey fetus, for example, arrives on its birthday with 70 percent of its cerebral development already behind it, and the remaining 30 percent is finished off in the next six months. A chimpanzee completes all of its brain growth within twelve months of birth.
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You and I, however, came into the world with a brain that weighed a mere 23 percent of what it would become in adulthood.
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even arriving in our early, fetal state, with less than a quarter of our brain development under our belts, we are still born with remarkably large brains.
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this approach to brain development is so extraordinarily strange and rare that it is unique in nature.
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evolution doesn’t plan. It simply modifies randomly and moves forward. And in this case, remember, remaining in the womb full term was out of the question. For us it was be born early, or don’t be born.
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we simply haven’t yet gathered enough clues to know precisely when an early birth became unavoidable. There are, however, a few theories.
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Some scientists believe earlier births would have begun when the adult brain of some predecessor or another reached 850 cc.
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The lake, the streams and the rivers that fed it, and the variability of the weather made the area a kind of smorgasbord of biomes—grasslands, desert, verdant shorelines, clusters of forest and thick scrub. The bones of the extinct beasts that lie by the millions in the layers of volcanic ash beyond the shores of Lake Turkana today attest to its ancient popularity.
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In fact it was so well liked that Homo ergaster, Homo habilis, and Homo rudolfensis were all ranging among its eastern and northern shores 1.8 million years ago
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Viewed from either end of the spectrum, none of the clues about his age have made much sense to the teams of scientists who have labored over them. Each was out of sync with the other. Some life events were happening too soon, some too late, none strictly adhering to the growth schedules of either modern humans or forest apes. Still, the skeleton’s desynchronized features strongly suggested that the relatives of this denizen of Lake Turkana were almost certainly being born “younger,” elongating their childhoods and postponing their adolescence. Apes may be adolescents at age seven and humans at age eleven, but this creature fell somewhere in between.