Humans are not unpunished by extinctions of large herbivores – then or now

What triggered the decline and eventual extinction of many megaherbivores, the giant plant-breeding mammals that roamed the Earth millions of years ago, has long been a mystery. These animals, which weighed at least 1,000 kg and included the eldest parents of elephants, rhinos, hippos and modern giraffes, reached a peak of diversity in Africa some 4.5 million years ago, in the Pliocene period (between 5.3 and 2.6 million years). . After that, their numbers slowly declined, in a trend that continued until the Pleistocene (2.6 million years ago, about 11,000 years ago).

This climate has been blamed on both the Earth's climate and hominins – our first human ancestors. However, a recent article has argued that the gradual extinction of megaherbivores was due to long-term environmental changes and that the behavioral evolution of hominins – such as the handling of tools and tools. use of fire – did not affect the decline of megaherbivores.

Although this seems to be true of the early decline of the megaherbivore population, we say that our ancient human ancestors may have contributed to more recent extinctions of megaherbivores. In addition, we are rehearsing the model today.

Ancient hominins in the land of giants

Genre Australopithecus is among the best known hominins of the Pliocene. Dating back to 4.2 million years, they shared a dozen species of large herbivores, including three giraffes, two hippos, two rhinoceros and five proboscidian species – a group of trunks and animal tusks that includes modern elephants and extinct mammoths and mastodons.

Australopithecus were omnivorous – but nothing indicates that they hunted large mammals. In fact, it is likely that megaherbivores played a beneficial ecological role for these first hominins. Thousands of years of grazing and migration have gradually opened wooded environments, which has created a perfect mix of woodlands and grasslands in which primitive hominins flourished. In these Pliocene landscapes, our ancestors and ancestors of modern elephants, rhinos, giraffes and hippopotamuses coexisted in relative harmony.

However, major climate and environmental changes had to separate the fate of hominins and megaherbivores. From the late Miocene (just before the Pliocene), then in the Pliocene and Pleistocene, ocean waters began to cool, atmospheric emissions of CO₂ began to decline, and in East Africa, grasslands began to expand, reducing forest cover. There is also evidence of more and more frequent fires.

Early hominins such as Australopithecus, comfortable in the grasslands and forests, were well adapted to these changing climatic and environmental conditions, as evidenced by their rich fossil record on several sites in Africa. However, megaherbivorous species that were only comfortable in wooded environments are struggling to survive.

Changing the behavior of hominins

At the time, more sophisticated hominines such as Homo erectus According to the authors of the recent study, megaherbivores appeared 1.8 million years ago already in decline for more than two million years. But that does not mean that Homo erectus did not sink the last nails into the collective coffin of megaherbivores. We believe that current archeological records are too poor to document the effects of hominin behavioral innovations, such as the use of tools, on extinctions of large Pleistocene mammals.

For example, we do not know how early use of fire – probably about 1.5 million years ago – influenced the landscapes and eating habits of large herbivores. In addition, nothing clearly indicates when hominins started to hunt large herbivores. Could they have hunted large mammals during periods of drought, as do some carnivores today? We think that the question of the role of hominins such as Homo erectus in the decline of megaherbivores remains open, despite the results of the recent study.

With the approach of more recent times in the history of the Earth, there is strong evidence that our species, Homo sapiens, played a major role in the wave of global megaherbivorous extinctions that occurred in the late Pleistocene, about 50,000 to 10,000 years ago. At that time, hominins developed over a large part of the globe and became sophisticated hunters of large animals. It was during this period that species of mastodons, woolly rhinos and lazy ground giants, among many others, were eventually exterminated.

A new wave of extinction

Of course, nowadays humans are responsible for such deep biodiversity loss that we may be experiencing a "sixth mass extinction", a calamity comparable to the worst biodiversity crises the Earth has seen since , 5 billion years old. Current evidence shows that human encroachment and hunting are destroying the natural environments of large herbivores such as elephants, rhinos, giraffes and hippos, leading to the decline of their populations.

But in the sea of ​​bad news of ongoing extinctions and habitat degradation, there are islands of hope that all is not lost. At the southern end of the Great Rift Valley in East Africa, Gorongosa National Park, Mozambique, is witnessing a rebirth of biodiversity. Populations of elephants, hippos and other mammals are increasing. Gorongosa shows us that with long-term planning and collaboration with local people, it is not too late to allow degraded ecosystems to rebuild and that, if the opportunity arose, nature had an amazing capacity for resilience.

Understanding the current biodiversity crisis from the depth-of-times perspective can help guide our efforts to conserve and restore the ecosystems we need for our own survival. Modern species of elephants, hippos, giraffes and rhinos are survivors of the deep past. The elephantidae appeared in the East African fossil record at about the same time as the early hominins and probably helped to shape the landscapes where our homin ancestors flourished. It is paradoxical that the single surviving hominin species is currently planting megaherbivores, as well as many other life forms, on the brink of extinction. We do it at our own risk.

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