Prehistoric Graves Reveal Americas' First Baby Boom
for National Geographic News
|January 9, 2006|
A new study of prehistoric cemeteries in North America is adding weight to the theory that the development of agriculture helped fuel baby booms around the world.
According to the theory, populations swell when societies shift from a nomadic hunter-gatherer lifestyle to one based on the more sedentary routine of farming.
Staying put allows women to have more babies, and a farming economy provides more food to support the growing population, explained Jean-Pierre Bocquet-Appel, a researcher at the National Center for Scientific Research in Paris.
North America's first baby boom is reflected in the number of skeletons of children ages 5 to 19 found in ancient cemeteries across the continent, he said.
"That doesn't mean the living condition was worsening," Bocquet-Appel said. "It means there were plenty of young people everywhere, and because there were plenty of young everywhere, there were plenty of young who died."
When populations are stagnant or decreasing, by contrast, graveyards are full of old people but few young, he added. According to the theory, a cemetery's population reflects the living population around it.
Bocquet-Appel and anthropology graduate student Stephan Naji analyzed skeletal remains in 62 prehistoric North American cemeteries.
They found that the number of immature skeletons increased by 37 percent over a 600-to-800 year period that coincides with the adoption of farming in North America about 2,500 years ago.
The researchers will report their findings in the March-April issue of the journal Current Anthropology.
The baby-boom pattern has been observed in African and European cemeteries dating about 5,000 to 7,000 years earlier, according to Bocquet-Appel. This period also coincides with the shift in those regions from foraging to agriculture at the end of the Stone Age.
The researcher said the current study is the first to expand the theory to a worldwide scale.
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.
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 moveas nomadic hunter-gathering societies arethey 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 explosionrising 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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