Colby Cosh: Planets could be the reason early humans revolutionized farming

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It’s one of the great paradoxes of human origin: why in the blazes did we invent agriculture? The Neolithic transition from nomadic life to permanent agricultural settlements is recognized as our species’ first step toward the form of social organization we have now, leading to the existence of cities, states, literacy and nations. For almost a hundred years, the switch from hunting-gathering to farming has been acknowledged as a “revolution.”

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But this wasn’t a revolution that happened in one place and spread outward. Human self-domestication happened at least a half-dozen times across the globe, and on all of the large continental landmasses. Farming was discovered independently over a period of millennia by widely separated groups from New Guinea to Mesoamerica, peoples that had no possible contact with one another.

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The paradox is that in all these places, the Neolithic Revolution and its corresponding social complexity seem to have led to an immediate decline in general living standards. Archaeological evidence suggests that humans who “decided” to live off crops of primitive grains seem to have had, for a long time, lower life expectancies and poorer physical health than contemporary hunter-gatherers.

Their skeletons are shorter, a lot shorter, and the bones show more signs of chronic malnutrition and infectious disease. The early farmers were making a shift to a way of life higher in both mortality and fertility, and they couldn’t have known in advance that their new culture was more conducive to further social evolution than one based on hunting.

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There are a lot of Grand Theories about the multiple Neolithic Revolutions, and a new one by a 40-year-old Italian economist, Andrea Matranga, is the talk of econ Twitter this week. Matranga’s paper, “The Ant and the Grasshopper,” has been accepted by the Quarterly Journal of Economics, which is in itself a reputation-making achievement. It’s all the more impressive because the paper is sole-authored, and Matranga’s current academic platform is an assistant professorship at the unprepossessing Chapman University in Orange, Calif.

Matranga’s own explanation for the invention of agriculture is: “Believe it or not, it is down to extraterrestrial forces.” Yes, that’s an actual quote from a cheeky Twitter thread in which Matranga summarizes his hypothesis colourfully. The real idea is that the period of the Neolithic Revolutions coincided with a time when seasonal temperature and rainfall differences were maximized by coinciding features of Earth’s orbit — features attributable mostly to Jupiter’s gravitational tug on us.

The Earth goes around the Sun, or so they would have you believe, and Earth’s rotational axis is tilted relative to the Sun, which creates the seasons. But the Earth’s motion has other subtle wobbles and shimmies caused by Jupiter: the eccentricity of its elliptical orbit grows and shrinks, and the rotational axis “precesses,” or wobbles, meaning that the face of the Earth pointing toward the Sun at our closest approach to it changes over time.

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The implication of this is that over a period of millennia, and particularly in what we think of as the “temperate” zones, the magnitude of climate seasonality will itself change in a somewhat chaotic way. For some periods much longer than a human lifetime, seasonal changes might be almost beneath notice; a few millennia later, they become a dominant feature of human experience. And one hemisphere of the planet — say, the northern one — might end up with a lingering developmental advantage because it was favoured at the right moment by the precession of Earth’s axis.

Matranga pulls together a lot of math, astronomy and geography to show that the local Neolithic Revolutions coincide with maximum local seasonality, and then he builds some economic models of primitive society to suggest what effect this might have had on social organization and population evolution. Alfred Marshall would have told him to burn this part of his paper, but perhaps the equations are necessary for appearances. The crucial point is that Matranga has found a strong possible explanation for the Neolithic paradox — why, and when, humans in many places adopted a form of social organization that seems to have left most of them worse off on average.

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For it’s not just the average that matters. In a world that was more or less the same year-round, hunter-gatherers didn’t have to worry about food storage: they could migrate cyclically within a small range, following wild game, to keep up with modest seasonal effects. But if the seasons then got more intense, food storage would become more important to the long-term survival of the group: one winter could now finish everyone off.

Those hunter-gatherer skeletons from Neolithic times really are bigger and stronger than those of the farmers, but they are also marked noticeably, Matranga says, with “Harris lines” like the rings of a tree — a biological signal of periodic starvation. Those sedentary idiots eating grass — ancestors to most of us — might have been hungry year-round, but they prevailed, and eventually stumbled their way into civilization. For better or worse, as some would say.

National Post

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