In “Genes Confirm Europeans’ Blow to Native Americans” (Science, December 9, 2011), Michael Balter tells us,
Now, a study published this week in the Proceedings of the National Academy of Sciences pushes the pendulum back toward dramatic population declines. Using both modern and ancient mitochondrial DNA (mtDNA) from Native Americans, an international team concludes that about 500 years ago, the number of reproductively active Native American women quickly plunged by half, indicating a “widespread and severe” contraction in population size.
Disease has been fingered by many sources, as well as Europeans’ violence.
Anthropologists and historians have argued about such uncertainties for decades, in large part because estimating early Native American population numbers is very difficult. Most researchers agree that in North America north of Mexico, Native Americans numbered only about 500,000 by the year 1900. But estimates for the year 1500 have varied wildly, from 20 million to just over 1 million, thus generating dramatically different percentages for post-European contact population crashes. (The Native American population has since rebounded, reaching about 3 million in the United States today.) “The demographic history of the Americas before and after Columbus has been among the most hotly debated topics in archaeology and history,” says anthropologist Clark Larsen of Ohio State University in Columbus.
One problem is that political pressure influences the estimates, up or down.
Because mtDNA is inherited through the mother, the pair was able to estimate the so-called effective population size—in this case the number of women actually bearing children— from the time of the peopling of the Americas about 15,000 years ago to nearly the present day. The team found that this number reached its highest point about 5000 years ago and precipitously declined, by about 50%, about 500 years ago. It then began to rise again. (The team did not try to estimate actual population numbers, because the relationship between effective population size and total population size can vary widely.)
Five thousand years ago is about 3000 BC, roughly contemporary with other developments in civilization elsewhere in the world.