North America once hosted many species of large mammals. These include the giant, elephant-like mammoths and others, such as gigantic sloths, beavers, and armadillos. Then, something happened, and by about ten thousand years ago, most North American animals weighing more than a hundred pounds were extinct. One suspect in this mass extinction mystery is humanity.

It’s thought that human groups specializing in big game hunting began arriving in the Americas about fourteen thousand years ago and rapidly spread, devastating animal populations wherever they went. However, the evidence for human guilt is only circumstantial. Humans may have entered and spread across the Americas at roughly the right time to be the culprit. Critics point to limited archeological evidence of hunting on the massive scale needed to produce the extinction. Some point to another suspect: rapid climate change.

In 2021 a team of researchers from Germany published an analysis of the geological evidence grounded in new statistical techniques. Their analysis supports the climate change hypothesis. The researchers claimed that variations in the abundance of large mammal species were better correlated with changing climate than with evidence for human presence. Large mammal populations appear to have increased as the climate warmed near the end of the last ice age about fifteen thousand years ago. The extinctions may correspond to a period during which the warming was abruptly interrupted by a time of drastic cooling called the Younger Dryas period, about thirteen thousand years ago. Researchers think the relative suddenness of the changes would cause significant ecological disruption.