It Will Take Mammals Millions Of Years To Recover From Humanity

The black rhino, like many large mammalian species alive today, is at a high risk of extinction. Stuart G Porter/Shutterstock

Mammal diversity is dwindling to such a degree that it will take 3 to 5 million years to restore current levels of biodiversity and 5 to 7 million years to return biodiversity to pre-human levels. And that's only if extinction rates fall back to natural levels within 50 years, a study published in the Proceedings of the National Academy of Sciences has found.

"Although we once lived in a world of giants: giant beavers, giant armadillos, giant deer, etc., we now live in a world that is becoming increasingly impoverished of large wild mammalian species," Jens-Christian Svenning, an ecologist at Aarhus University and study co-author, said in a statement.

"The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly."

This is the sixth mass extinction in 450 million years and the only one not caused by a natural disaster but rather the destructive activities of one species (in this case, us). In the first five mass extinctions, biodiversity very slowly crept back to previous levels with evolution filling the gaps with a wave of new species. Now, researchers at Aarhus University have used advanced evolutionary simulations to predict how long it would take to return to the levels of biodiversity we see today if pollution, poaching, and habitat destruction (and, therefore, extinction levels) return to natural levels in 50 years or less. 

To do so, the team regenerated 2.5 billion years of evolutionary history using an extensive database of mammals, both alive and extinct. Their models accounted for the fact that many species alive today (including the black rhino) are facing extremely high rates of extinction – the Asian elephant, for example, has less than a 33 percent chance of surviving into the next century. Using data on the evolutionary relationships and body sizes of all the different mammalian species, the team worked out the amount of time that would be lost from past and potential future extinctions, and how long it would take to recover.

How the smaller mammals will have to evolve and diversify over the next 3-5 million years to make up for the loss of the large mammals. Matt Davis/Aarhus University
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