Humans quit for the extinction of African mammals

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New research has challenged a long-held view that early humans helped eliminate many of the large mammals that once roamed Africa.

Today, Africa has five massive mammal species that eat plants. but there are millions of years ago, there were many more types of giant herbivores.

It is unclear why so many guys have gone, but many experts have blamed our ancestors for tooling and eating meat.

Now, researchers say that the decline of mammals began well before the appearance of humans.

In the journal Science, Tyler Faith, of the Natural History Museum of Utah, and his colleagues say that long-term environmental changes have been at the root of extinctions.

This mainly took the form of an expansion of grasslands, in response to lower levels of atmospheric carbon dioxide (CO₂).

"Despite decades of literature claiming that early hominins (human parents) had an impact on ancient African faunas, few attempts have been made to test this scenario or explore other solutions," said Dr. Faith.

A shift from predominantly vegetable and fruit consumption to predominant meat consumption may have resulted in the evolution of large human brains. This transition occurred in conjunction with the development of stone tools, which would have allowed our ancestors to butcher carcasses of animals; either as scavengers or hunters.

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To determine whether humans played a role, researchers compiled a record of seven million extinct herbivores in East Africa. They focused on the larger species, megaherbivores, which weigh more than 2000 lbs (907 kg).

Today, only elephants, hippos, giraffes and white and black rhinos fall into this category.

But the three million-year-old human parent "Lucy" (Australopithecus afarensis) shared its East African habitat with three species of giraffe, two species of rhinoceros, one hippopotamus and four elephant-like species.

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The results of the analysis showed that in the last seven million years, about 28 large mammal lines have disappeared in Africa.

In addition, the decline of herbivores began about 4.6 million years ago and the rate of decline has not changed since the onset of Homo erectus, one of the oldest human ancestors who could have contributed to the extinctions.

"This process of extinction began more than a million years before the earliest evidence of human ancestors making tools or dismembering animal carcasses and well before the appearance of any kind of hominins capable of to hunt them, as for example: Homo erectus, "said Dr. Faith.

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The researchers also examined the recordings of climate and environmental trends. They conclude that climate is a much more likely culprit than humans. Climate change seems to be causing the replacement of large shrubs and trees with grasslands.

"The key factor in the decline of Plio-Pleistocene megaherbivores appears to be the expansion of grasslands, which is likely related to an overall drop in CO₂ in the atmosphere over the past five million years. "said co-author John Rowan, of the University of Massachusetts at Amherst. .

"Low levels of CO₂ favor tropical grasses over trees, and as a result, savannas have become less woody and more open over time.We know that many extinct megaherbivores feed on woody vegetation, so that They seem to be disappearing parallel to their food source. "

The loss of large mammals in Africa could also explain other extinctions that have been blamed on our ancient ancestors.

For example, some scientists have suggested that increasingly carnivorous human groups lead to a decline in the number of predators and scavengers.

"We know that there are also major extinctions among African carnivores and that some of them, like saber-toothed cats, may have specialized on very large prey, perhaps juvenile elephants, "said co-author, Professor Paul Koch, of the University of California Santa Cruz (UCSC).

"Some of these carnivores may have disappeared with their megaherbivorous prey."

In the same issue of Science, René Bobe and Susana Carvalho, of Oxford University, warned against some conclusions: "It is not clear what ecological role hominins played in the long evolutionary history of megaherbivores. in Africa and how these roles have changed over time and have varied from one geographic area to another.

"Another question concerns the time when hominines have become systematic predators of animals larger than themselves."

They added: "The causes of megaherbivorous decline are probably complex, multidimensional, and variable in time and space.The precise timing of major behavioral innovations among hominans remains poorly limited by current archaeological and palaeontological records." .