Big Mammals Went Extinct Because Of Ancient Humans, Reveals Study

If man's impact on big animals continues on its current trend, in 200 years the largest mammal on Earth will be the domestic cow.

3d illustration of prehistoric men hunting a young mammoth.
Esteban De Armas / Shutterstock

If man's impact on big animals continues on its current trend, in 200 years the largest mammal on Earth will be the domestic cow.

Early humans are to blame for the extinction of Earth’s big mammals shows a new study published today (April 20) in the journal Science.

The research points out that our impact on larger animals, which even now is increasing their risk of extinction, is not a new thing but actually dates back to man’s very beginning.

It seems that long before the earliest hominids first emerged, animals were a lot bigger than those that are still around today. About 2.6 million years ago our planet was populated by massive mammals, such as wooly mammoths as well as elephant-sized and monstrous saber-toothed cats, reports USA Today.

As soon as our early ancestors learned how to hunt and began targeting the big beasts of the late Pleistocene, our planet’s larger animals began to slowly disappear, evolving into the smaller, better-adapted versions we see today.

According to lead author Felisa Smith, a paleoecologist at the University of New Mexico, her team combed through “the entire fossil record for 65 million years, in million-year increments,” to see at what point big size became a disadvantage.

“For 65 million years, it didn’t matter what size you were,” she said in a statement.

Then, as soon as we hit the scene, Earth’s mammals started to shrink because it was “bad to be big.”

Although there were many factors involved that ultimately led to the disappearance of Earth’s largest mammals — as giants progressively died out and animals were forced to relinquish their big body size in order to adapt to the new world — the spread of hominids and humans all over the seven continents played a major role.

“This decline is coincident with the global expansion of hominins over the late Quaternary,” the authors write in their paper.

That was the moment when Earth’s largest mammals started dying out at a rate “unprecedented in 65 million years of mammalian evolution,” the research reveals.

“It wasn’t until human impacts started becoming a factor that large body sizes made mammals more vulnerable to extinction,” study co-author Kate Lyons, from of the University of Nebraska-Lincoln, told USA Today.

She stated that the extinction of larger animals “occurred not very long after the birth of us as a species” because “it just seems to be something that we do.”

The rise of Homo erectus 1.8 million years ago came with a shift in the diet of hominids, who started to depend a lot less on plants and focus on hunting for meat.

Logically, bigger groups went after bigger animals, Smith points out.

“You hunt a rabbit, you have food for a small family for a day. You hunt a mammoth, you feed the village,” she said.

Even though Earth’s mighty creatures clearly became a food source for the fast-rising hominids, it’s also possible that we targeted larger mammals not just out of hunger.

Ancient humans might have started going after them to eliminate competition — as it happens today in the case of wolves, elephants, orangutans, and the big cats of Africa. Even now large animals are hunted down if they infringe on human settlements and steal livestock and crops.

Surprisingly, the research unveiled that wherever hominids went, animals drastically dropped in body size. Over the course of 100,000 years, mammals lost about 50 percent of their average body size, Smith’s team uncovered.

Africa now harbors Earth’s largest mammals, but 125,000 years ago animals here had already shrunk and were about half smaller than on the rest of the continents.

“We suspect this means that archaic humans and other hominins had already influenced mammal diversity and body size,” said Smith.

In Australia, mammals’ average body size is now just one-tenth of what it used to be 125,000 years ago. In North America, mammals have shrunk on average from 216 pounds to about 17 pounds – the size of a bobcat – states the Washington Post.

And the trend is still going on, largely because of us.

“If the current trend continues, terrestrial mammal body sizes will become smaller than they have been over the past 45 million years,” warn the researchers.

Based on the study’s predictions, if man’s influence over the shrinking of animals keeps up its current pace, the largest mammal we’ll be seeing 200 years from now will be the domestic cow, the Washington Post reports.