Earth’s Mammal Size Decreased Due to Geographical Spread of Humans

Earth’s mammal size decreased due to geographical spread of humans around the world. Just roughly 120,000 years ago, life on Earth used to look a lot more imposing.  There were the six-ton giant ground sloth in South America, Bunyanesque beavers that weighed as much as an NFL linebacker, the 350- to 620-pound sabertooth cat in North America, the six-ton wooly mammoth in North America and Eurasia, and the two- to three-ton wooly rhino in northern Asia and Europe. It’s tough to imagine the world occupied with large animals like these.


But, throughout the time, the size of all of these animals became less so rapidly that scientists still can’t fully explain the reason behind this reduction.

Now, a new study published in the journal Science on Thursday claims that humans and other hominids were the main driving forces.

a team of biologists led by Felisa Smith, a paleoecologist at the University of New Mexico, Albuquerque, looked at the entire fossil record for 65 million years with an aim of providing a different perspective on this disappearance.

Their research discovered that decrease in mammal size was occurring simultaneously with the geographical spread of humans around the world. The researchers said that big animals don’t reproduce as fast as small ones and so humans had a major impact on mammal populations.

“This finding suggests that the homogenization of natural ecosystems was a consequence of hominid behavior in general and not specific to H. Sapiens,” Smith and her colleagues wrote. “As mammals play a critical role in shaping ecosystems, the downsizing trend will have a cascading impact on other organisms.”