Spread of humans results in the destruction of mammals

From an average weight of 100 kilos about 125,000 years ago to less than 17kg now; and shockingly, to less than 3kg in just 200 years. That is the sordid story of extinction of mammals around the globe as human civilisation spread across the globe.

A study published in the journal Science warns that in 200 years the domestic cow would be the largest terrestrial mammal left. But the average weight of mammals would have plunged to less than 3kg, the size of a Yorkshire terrier.

According to Felisa Smith, the lead author of the study and a professor of biology at the University of New Mexico, “mammalian body size around the globe will revert to what the world looked like 40 million years ago.”

Long, long ago – between 2.6 million and 12,000 years ago – massive mammals roamed around the earth. They included elephant-sized ground sloths, saber-toothed cats and wooly mammoths. Unfortunately, they are all extinct now, as human civilisation spread across the globe.

And these creatures did not disappear, as is commonly believed, because of climate change on earth. Smith believes that shifting climates including the setting in of ice age, caused adaptations in animals, but was not the primary cause of their extinction.

It was only after the spread of human beings that large-bodied mammals started getting extinct. And it began to happen only after the emergence of humans as a species, says the study.

Surprisingly, about 125,000 years ago the average body size of mammals in Africa was half that of those in other continents. This was the time when archaic humans and other hominins had set root in Africa.

Smith says the only time bad in the animal world is when humans are involved. “We are efficient predators and have been for a really long time — so there's not a value judgment here — it's just what hominids did,” she said.