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Science and Innovations

Earth Notes: The Colorado Plateau’s Prehistoric Baby Boom


One of the enduring mysteries of the Colorado Plateau is why the area’s ancient Puebloan population dropped to almost zero in the late 13th century, after peaking at as many as 40,000 people just 30 years earlier.

A new theory advanced by Washington State University researchers suggests that a poorly timed “baby boom,” coupled with extreme drought and an over-dependence on corn, was the reason.

Anthropologists examined evidence from hundreds of ancient sites to get a fix on what the region’s birthrates were. They found that long before Columbus, those rates reached a level exceeding even the highest on Earth today.

The researchers looked at statistics based on skeletal remains, as well as the transition in the use of tools for cutting meat to those used for pounding grain. Those data document a dramatic shift toward irrigated agriculture that occurred before extreme droughts began in the mid-1100s.

By that time, corn alone may have provided 80 percent of the calories people burned.

When the area’s climate got hotter and much drier, farming no doubt grew more difficult. The population appears to have grown too large to feed itself. As a result, thousands may have died of hunger or thirst, while others moved to the few places that still had reliable water.

The precise reasons for the big population drop will remain subject to debate. But, the new study is evidence that population growth in our fragile environment has clear consequences — and parallels in local history.

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