Human history in a nutshell, Part 1: Evolution

It was about six million years ago that we last shared a common ancestor with a biologically distinct gang — chimps and other apes. But our species, Homo Sapiens, is only a couple of hundred thousand years old. Between those two chronological markers, a lot of evolution happened.

In fact, over those six million years, quite a large number of more or less “human” or proto-human species came and went. The line of descent that produced us was only one of many. All the others petered out.

As the story unfolded among all these variant creatures, two different basic strategies evolved. Call one vegetarian. Its practitioners relied on a menu much like that of modern apes — fruits, nuts, berries, etc. A pretty reliable diet, but due to low nutritional content, much energy was devoted to eating and digesting — they literally had to consume a lot to get the energy to consume a lot. A big digestive system was required, diverting resources that otherwise could have gone to their brains.

The other group went for brains rather than guts. This required a high energy diet, i.e., including meat. But meat was hard to get, for such weak little critters lacking fangs and claws. Getting meat required brains.

All well and good, except that bigger brains meant bigger heads, a bit of a problem for mothers giving birth. And that was exacerbated by a second evolutionary trajectory. Hunting meat proved to be a lot easier for early humans if, instead of going on all fours, they could efficiently walk upright and even run. Doing that called for changes to pelvic architecture, which had the effect of narrowing the birth canal. So the bigger-headed babies had to fit through a smaller opening. Something had to give.

What gave was the gestation period. If humans functioned otherwise like apes do, babies would spend not nine months in the womb but twenty, and come out ready for action. But their heads by twenty months would be so big they couldn’t come out at all. So we make do with nine months, about the limit mothers can bear, and the least babies can get by with. Consequently they require lengthy attentive nurturing, which of course has had a vast impact upon humans’ way of life.

Earlier birth thus meant longer childhood, and a lot of a person’s development outside the womb as his or her brain responds to things around it. This in turn is responsible for another huge fact about human life: we are not cookie-cutter products but very different one from another. And that fundamental individualism, with each person having his own perspectives and ideas, played a great role in the evolution of our culture and, ultimately, civilization.

Another key part of the story was fire. We romanticize the mastery of fire (e.g., in the Prometheus myth) as putting us on the road to technology. But that came much later. Fire was our first foray into taking a hand in our own evolution. It began with cooking. Remember that trade-off between gut and brain? Cooking enabled us to get more nutrition out of foods and digest them more easily. That enabled us to get by with a smaller gut — and so we could afford a bigger brain.

This omnivorous big-brain model seemed to work out better than the vegetarian one; the vegetarians died out and the omnivores became us. (This is not intended as a knock on today’s vegetarians.) But notice again how much actually had to be sacrificed in order to produce our supersized brains. And that this was a bizarre one-time fluke of evolutionary adaptation. It happened exactly once. None of the other zillions of creatures that ever existed ever went in this unique evolutionary direction.

In other words, if you think evolution of a species with world-dominating intelligence was somehow inevitable or pre-ordained, consider that it didn’t happen for 99.999+% of Earth’s history. It was an extreme freak in the workings of evolution.

Indeed, it’s a mistake to conceptualize “evolution” as progress upward toward ever greater heights (culminating in Homo Sapiens). It’s because of that erroneous connotation of progress that Darwin didn’t even use the word “evolution” in his book. The process has no goal, not even the “selfish-gene” goal of making things good at reproducing themselves. It’s simply that things better at reproducing proliferate, and will grow to outnumber and eclipse those less good at reproducing. Our species happened to stumble upon a set of traits making us very good reproducers. But insects are even better at it, and there are way more of them than us.

(Much of what’s in this essay came from reading Chip Walter’s book, Last Ape Standing.)

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