Ancient Southwest Baby Boom Offers Lesson in Overpopulation

By April Reese | June 30, 2014 2:57 pm
Sites like Pueblo Bonito in northern New Mexico reached their maximum size in the early A.D. 1100s, just before a major drought began to decrease birth rates throughout the Southwest. Credit: Nate Crabtree Photography

Sites like Pueblo Bonito in northern New Mexico reached their maximum size in the early A.D. 1100s, just before a major drought began to decrease birth rates throughout the Southwest.
Credit: Nate Crabtree Photography

With 7 billion people now inhabiting the planet — more than at any other time in history — you’d think we’re having more babies than ever before. But a millennia ago, birth rates were actually higher in the Southwest than they are anywhere in the world today, researchers have found. Back then, the regional population soared — and then crashed eight centuries later. Can modern-day humans learn anything from the ancient Puebloans’ downfall?

Indeed we can, says a team of anthropologists at Washington State University, who report surprising population trends in the first millennial Southwest in as study published today in Proceedings of the National Academy of Sciences.

Tracking the Boom 

Sifting through a century’s worth of data on thousands of human remains found at hundreds of sites across the Four Corners region, the area where modern-day Arizona, New Mexico, Colorado and Utah meet, the researchers crafted a detailed chronology of what’s called the Neolithic Demographic Transition, when people began eating more grain and less meat.

WSU anthropology professor Tim Kohler and graduate student Kelsey Reese put the start of the ancient population boom in the region at around 500 A.D. By that time, people had adopted two of the hallmarks of civilization: settled agriculture and food storage. They were growing mostly maize, which had become a dietary staple, accounting for about 80 percent of calories. With plenty of food to go around, crude birth rates — the number of newborns per 1,000 people per year — increased steadily.

But those halcyon days came to a sudden end around 1300. Within 30 years, the northern Southwest was virtually uninhabited.

Mysterious Decline

It’s likely that Mother Nature played a significant role in the population’s decline: A major drought that gripped the area in the mid-1100s was the beginning of the end, Kohler says. Until about 1280, the farmers left and conflicts raged across the northern Southwest. But the babies kept coming.

“They didn’t slow down — birth rates were expanding right up to the depopulation,” he says. “Why not limit growth? Maybe groups needed to be big to protect their villages and fields.”

As many as 40,000 people lived in the region in the mid-1200s, but suddenly, it emptied out. No one is really sure why, but Kohler suspects the population became too big to feed itself as the climate changed and growing conditions worsened. And as people began to leave, the community deteriorated, making it more difficult for anyone staying behind to fight off intruders and build and maintain infrastructure, he says.

Interestingly, people in the southern Southwest, who had developed irrigated agriculture, did not experience the same population boom their dryland-farming neighbors to the north did.

Consequences of Growth

Kohler says the Sonoran and Tonto people, who inhabited what we know today as southern Arizona, probably didn’t have more children because it would have been difficult to develop more farmland for them to use given limited surface water supplies. And water from irrigation canals may have carried harmful disease-causing bacteria and viruses, he adds. Groups to the north, who relied on precipitation from the skies to water their crops, would have been able to expand maize production into new areas as their populations grew — until the drought came.

Whatever caused the northern ancient Puebloans’ decline, Kohler says, their fate shows that “population growth has its consequences.”

He points to the warning of Thomas Malthus, who warned back in the 18th century that humans would eventually become too numerous for Earth’s limited resources to support.

Despite huge advances in farming and food distribution systems, modern-day humans are still vulnerable to catastrophic changes, and shouldn’t take for granted the resources and climate we depend upon for survival, he says. Kohler: “We can learn lessons from these people.”

CATEGORIZED UNDER: Living World, top posts, Uncategorized
  • disqus_0NaovmuWmf

    It’s not likely that we will benefit from any historical information. Humans are notoriously inept at learning from history and past mistakes.

    • Imskeptical

      Plus, we have LOTS of reasons to drastically limit population right now, to which we do not appear to be paying attention: we are exhausting water supplies and habitat, polluting vast areas of land, air and water, and driving so many entire species to extinction. We won’t know we have reached the “tipping point” until we are well past it and it is too late.

      • SueAltringhamlat

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        Allison recently got a nice 6 month old Jaguar by working from a macbook.this website C­a­s­h­d­u­t­i­e­s­.­C­O­M­

        • johnclark1

          OUT damn spamspot!

      • Daniel LaLiberte

        Population data show that we HAVE been reducing the population growth rate since 1980, and the growth rate is projected to reach 0 in another 60 years. Almost everyone is having FEWER children, not more. How does population grow then? Population growth is almost always caused by advances in technology or availability of resources so fewer children die of starvation and disease. People who are used to having 6 children when 4 would likely die need to get used to having only 2.

        • Imskeptical

          Really? Worldwide? If that is true, it’s wonderful news. The latest information I had was pretty depressing.

        • H. Bloom

          In 60 years the planets population will be at 50 billion. I doubt the earth can sustain that much pollution by people.

  • pto

    The US needs public policies that give people incentives to have two or three kids and no more and foreign and immigration policies that doesn’t ignore or reward the problems of overpopulation in other countries.

    Limiting benefits for more than three children for US citizens would be politically unsustainable and socially unfair if we are seeing disproportionate immigration from countries which are economically unsustainable at their current populations and are doing little or not enough to limit their own population growth.

    • JohnEightThirtyTwo

      Or we could supply contraception to people who want it. Oh wait, Father Scalia says that would be a sin.

      • pto

        It is a sin… But sometimes we have to choose the lesser of evils. Creating a world of scarcity through over procreation will create more evil through societal conflict than just having sex with someone for the pleasure will.

        • Les Borean

          “It is a sin…”
          Sit down for this shocker:
          You are not god

          • pto

            No, but I have sinned.

    • John Boyle

      The USSC has now allows corporations to deny birth control on religious grounds. It seems like they want more births and anti-abortions laws. Now religious groups want to get more rulings in their favor for anything or person they want to discriminate against. So this all means greater population growth.

      • pto

        Population growth means economic growth… Which means the elite will have more, but unfortunately unless technology can improve our production, then that means less and less for the rest of us. And even if technology does keep up, competition in the labor market will depress wages which will continue making the economic divide worse.

      • Ivar Ivarson

        Two birth control methods were objected to by the Hobby Lobby closely held corporation. Many other birth control methods were not objected to. The employees can get “Plan B” pills and IUD devices if they pay for them themselves (although I suspect that the relevant insurance companies will be required to ‘pay’ for it out of their profits by the regulators). No corporation was allowed to “deny” birth control to anyone.

  • JohnEightThirtyTwo

    The first paragraph seems to confuse the birth rate per thousand with the total number of births. The latter is what the cited study looked at. The former is what you’d think would now be at a peak.

  • Robert Futscher

    Other studies that include Mexico have found that when the population in the four corners region went down the population of Mexico went up. The theory being that when the government failed the people just moved. First to Mexico and then from Mexico to the Phoenix area.

  • realthog

    “But a millennia ago”

    “Millennia” is the plural; the singular is “millennium.”

  • Anechidna

    Our population growth is slowing, birth rates are dropping in all except a few locations and these are not high population regions. But we do need to be conscious of population and food production and the costs to the earths resources of that production and population levels.

    Malthus is an interesting person and like many today failed to see that we can adapt and survive. Although the threat of an uncontrollable pandemic exists even today in spite of our capacity for healthcare.

  • quadrill

    Great information ! How do they really know these population #s? Not critical ,just wondering*

  • Zacocom Zaccom

    The amount of pollution in food is scary. Heavy metals all around. Yet they still insist on mining that poison. Let alone asbestos in most buildings around the planet. Did you ever heard of the Aznalcóllar Mine in Spain which broke polluting Doñana National Park, one of the most marvellous places all along two provinces.

    Well they are opening it again, no kidding. Because the town responsible of the catastrophe kept breeding and now they want to give them employment at everyones health cost.

  • philconl

    It’s obvious, but nowadays we have to have sensationalized fear mongering pro government power and control spew explanations that everyone is INDOCTRINATED with.


    It seems as though the most common reaction to diminishing returns is to put more effort into the very thing that isn’t working anymore.


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