Researchers have discovered one of the greatest baby booms in the history of North America, and it could very well be the warning sign scientists are looking for that rapid population growth is not always a good thing.
Washington State University researchers have reconstructed a model of the Neolithic Demographic Transition in the Four Corners region of the Southwest United States and found that a Native American "growth blip" spanning several centuries took place between 500 and 1300 A.D.
The findings, which were published in the Proceedings of the National Academy of Sciences, reveal that the agricultural civilizations of that period experienced extremely high birth rates at a level that "possibly exceeded the highest in the world today," but it was followed by a mysterious crash. By the turn of the 14th century, the area was eerily empty.
"We can learn lessons from these people," says Tim Kohler, lead researcher and WSU Regents professor of anthropology.
Kohler and his colleague, graduate student Kelsey Reese, examined thousands of human remains including stone tools left in the area to map out a chronological sketch of the Neolithic Demographic Transition of the region, with the transition of stone tools from meat-cutters to grain-pounders reflecting the differences in crude birth rates, or the number of babies born per 1,000 persons.
Neolithic farmers in the region began growing corn around 2,000 B.C., but it was only a millennium and a half after that the population adapted. By 400 B.C., 80% of the average person's daily caloric intake consisted of corn. By that time, birth rates began soaring until around 500 B.C.
But birth rates varied by area. For example, the irrigation-dependent populations of the Sonoran Desert and Tonto Basin in what is now known as the state of Arizona had lower numbers than the people thriving in the San Juan basin and northern San Juan of New Mexico and southwest Colorado. This may be due to a variety of reasons, such as contamination of their irrigation channels or the ability of less advanced semi-nomadic communities to expand their farmlands.
Between 1000 A.D. and 1280 A.D., the region suffered from one of its worst dry spells, leading to wars and conflicts between communities fighting for limited resources. Surprisingly, birth rates remained high. Kohler notes communities perhaps needed to be bigger to protect themselves from warring neighbors. By the mid-1200s, the researchers say the population in the region reached as many as 40,000 people.
However, their numbers all of a sudden dropped to almost nothing some 30 years after, and anthropologists are scratching their heads over the mysterious disappearance of the human population in the region. Kohler believes that the population was too big to feed itself and, as people began leaving, the communities became too small to defend themselves and build infrastructure. This is, of course, just one of many guesses, but Kohler says the crash that followed the ancient baby boom is a sign that "population growth has its consequences."
