Mammals Will Still Be Recovering From Human Destruction Long After We're Gone

A somber new study estimates that it could take several million years for mammal diversity to recover from humanity’s impact.

Humans have helped propel the extinction of more than 300 mammal species — equaling a staggering loss of 2.5 billion years’ worth of unique evolutionary history, according to a grim new study published Monday.

It could take many millions of years for mammals to evolve enough new species to recover from the destruction humans have caused, researchers estimated. The human species, however, won’t likely survive to see the day.

“We are doing something that will last millions of years beyond us,” paleontologist Matt Davis of Denmark’s Aarhus University, who led the new research, told The Guardian of humans’ devastating impact on biodiversity.

The new study, published in the Proceedings of the National Academy of Sciences, estimates that it could take up to 5 to 7 million years for mammal diversity to be restored to the level it was before the arrival of modern humans — and that’s assuming people cease all poaching, pollution and habitat destruction in the next 50 years.

Like many scientists, Davis believes the world is currently in the midst of a sixth mass extinction, also known as the anthropocene extinction or one caused by human activity. Davis told The Atlantic this week that “what we are going through now could have as big an impact as the asteroid” that killed off most of the dinosaurs.

It’s a “pretty scary” situation we’ve created, Davis said. “We are starting to cut down the whole tree [of life], including the branch [humans] are sitting on right now,” he told The Guardian.

For the study, Davis and his colleagues focused not just on the number of species that have gone extinct but also on how much evolutionary history they represent (or the amount of time each species had spent evolving before it was wiped out).

As The Atlantic explained, this metric, known as phylogenetic diversity, provides a useful perspective as some species are particularly unique and irreplaceable:

The pygmy sloth, for example, may be one of the most threatened mammal species, but it’s also one of the youngest, having diverged from its closest relative 9,000 years ago. The aardvark, by contrast, is the last survivor of a once-large group of mammals that split off from the others 75 million years ago. Losing the pygmy sloth would be like snapping off a tiny twig from the mammalian family tree; losing the aardvark would be like sawing down an entire branch.

The study found that from the rise of modern humans to the 16th century, two billion years of mammals’ unique evolutionary history was wiped out. Since then, humans have helped erase another 500 million years ― and an additional 1.8 billion years could be lost in the next five decades if the high rate of mammal extinctions continues.

The endangered red panda, threatened by climate change and habitat destruction, has been identified by researchers as a creature with an especially rich and unique evolutionary history.
The endangered red panda, threatened by climate change and habitat destruction, has been identified by researchers as a creature with an especially rich and unique evolutionary history.
Rebecca Naden/Reuters

Davis said he hopes the new research will help guide conservation work, specifically in helping to identify ― and prioritize ― endangered species with long evolutionary histories. The study, for instance, highlighted the black rhino, red panda and the indri, a large lemur endemic to Madagascar, as endangered animals with particularly long and unique lineages.

“It is much easier to save biodiversity now than to re-evolve it later,” Davis said in a news release.

Ultimately, however, piecemeal conservation efforts won’t be sufficient to stem the tide of extinctions and avert “worst-case scenarios,” Davis stressed.

“It’ll probably get worse, in all honesty,” he told The Atlantic. ”[We need] a massive, ambitious global-scale project that everyone will need to be involved in.”

“It comes down to whether politicians have the political will to make this happen,” he added.

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