Early humans are not to blame for the extinction of large mammals in Africa several million years ago, a new study proclaims.

Tyler Faith, a curator of archaeology at the Natural History Museum in Utah, and his team disputed the long-held belief that early humans contributed to the demise of megaherbivores through hunting. Instead, the changes in the environment actually caused these animals to die out.

Do Not Blame Human Ancestors

There used to be a great number of megaherbivores — plant-eating animals that weigh about 2,000 pounds — in Africa. Right now, only five of them still exist, namely the hippopotamus, giraffe, elephant, white rhino, and black rhino.

Some scientists have always attributed the disappearance of these animals to the evolution of tool-bearing and meat-eating hominids. Apparently, that is not the case.

The study published in the journal Science looked at the 7-million-year record on herbivore extinctions in eastern Africa. The researchers found that some 4.6 million years ago, there had been a steady decline of megaherbivore diversity in the continent and it had started way before human ancestors began butchering animals. In fact, the decline started way before the appearance of any hominin species who were capable of hunting the large mammals.

Environmental Factors

The team of researchers also looked at independent records of environmental and climatic trends from the last 7 million years, particularly the global atmospheric CO2 and stable carbon isotope records of vegetation structures.

The analysis revealed that 28 lineages of megaherbivores became extinct. It coincided with the expansion of grasslands that caused a drop in atmospheric CO2 over the past 5 million years.

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

Moreover, the loss of megaherbivores millions of years ago might have also caused the extinction of other animals. African carnivores who thrived by eating the meat of juvenile elephants, for example, might have died out because of the disappearance of their primary prey.