Prehistoric Graves Reveal Americas' First Baby Boom

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The study is based on an idea first proposed in 1983 by anthropologists Lisa Sattenspiel, now at the University of Missouri at Columbia, and Henry Harpending, now at the University of Utah in Salt Lake City, that more immature skeletons found in a cemetery reflect a growing population.

"This is exactly what happens on average in the European, African, and North American cemeteries," Bocquet-Appel said.

He notes that as a general rule immature skeletons make up about 20 percent of a culture's graveyards before the advent of agriculture. This rises to about 30 percent as the shift to agriculture occurs.

Clark Larsen, an anthropologist at Ohio State University in Columbus, said the paper "makes a very good case" for the link between baby booms, fertility, and agriculture.

"I think it's quite neat," he added.

Population Pressure

According to Bocquet-Appel, baby booms are both the cause and the consequence of the shift from hunting and gathering to agriculture.

"The cause was probably a by-product of the sedentarism … . The change in mobility … has big consequences concerning the fertility of women," he said.

When women are on the move—as nomadic hunter-gathering societies are—they must carry their young. As a result, children are more likely to breast feed, which inhibits the mother's menstrual cycle and inhibits fertility, he explained.

In a farming community, children do not spend as much time in their mother's arms, lowering their opportunity to suckle. Without a suckling baby, a woman is able to have another child.

"[This] is in fact the very cause of the birth explosion—rising fertility," Bocquet-Appel said. "Meanwhile there is a new systemic economic regime, which has a bigger carrying capacity, which can feed a lot of mouths."

Both a sedentary lifestyle and a shift to an economy that increases the food supply are needed for a baby boom, he added.

For example, he said, a hunter-gatherer society that settles by the sea to eat fish for a hundred years may experience higher fertility rates from the sedentary lifestyle. But if they catch no more fish, they will not have sufficient food to feed the growing population.

"In that case, rapidly the population will probably crash," he said.

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