Low CO2 killed the megafauna star


As with the present day fauna and flora extinctions, humans have been traditionally blamed for the extinction events over the past several tens of thousands of years. Maybe not so anymore, regarding one particular one:

A new study disagrees with a longstanding view that humans wiped out large animals that previously occupied Africa.

In research published in the journal Science on Friday, authors analyzed records on megaherbivore communities in eastern Africa over seven million years. A megaherbivore is a mammal weighing more than 2,000 pounds. They concluded that extinctions of diverse mammal communities in Africa occurred before evidence of human hunting.

The animal decline might have instead been because of environmental factors such as declining atmospheric carbon dioxide and expansion of grasslands, researchers write.

“Low CO2 levels favor tropical grasses over trees, and as a consequence savannas became less woody and more open through time,” John Rowan, a postdoctoral scientist from the University of Massachusetts Amherst who was involved in the research, said in a statement. “We know that many of the extinct megaherbivores fed on woody vegetation, so they seem to disappear alongside their food source.”

Analysis suggests 28 lineages of megaherbivores went extinct, starting around 4.6 million years ago, according to lead author Tyler Faith, an assistant professor in the Department of Anthropology at the University of Utah. Today, only elephants, hippopotamuses, giraffes and white and black rhinoceroses exist.

So while today the scientific consensus blames man-made emissions of CO2 for the wave of extinctions over the past 50 years ago, it seems that the problem 50,000 years ago was that the early modern humans were not pumping enough CO2 into the atmosphere to save the big African mammals. We just can’t seem to get it right.

It’s safe to speculate that the African extinctions, just like the later American and north Asian ones, resulted from a mixture of factors, not just overeager Cro Magnon hunters. Humans are certainly capable of hunting species to extinction or near extinction – see the North American buffalo or the flightless dodo bird. Neither, however, has been decimated by the native peoples around them but by the modern, commercially-minded colonisers. The fact that neither the Americans nor Siberia host, for example, the mammoths anymore has as much to do with human migrations as with the climatic change following the end of the last Ice Age. I suspect thought that had there been environmental activists amongst the hunter and gatherer tribes of 10,000BC, they would have firmly pointed a finger of guilt at their fellow tribesmen for the disappearance of all sorts of big hairy creatures, from the sabre-toothed tigers to giant sloths. One thing we humans have always liked are simple explanations for complex phenomena. Oh, and blaming ourselves for everything.