Extinctions during human era worse than thought

9 hours ago A new and more precise recalculation of the normal background extinction rate what it would be without the human presence shows the rate to be lower, meaning that the rate of extinction in the human era is as much as 10 times worse than had been thought. Credit: Wikimedia Commons

It's hard to comprehend how bad the current rate of species extinction around the world has become without knowing what it was before people came along. The newest estimate is that the pre-human rate was 10 times lower than scientists had thought, which means that the current level is 10 times worse.

Extinctions are about 1,000 times more frequent now than in the 60 million years before people came along. The explanation from lead author Jurriaan de Vos, a Brown University postdoctoral researcher, senior author Stuart Pimm, a Duke University professor, and their team appears online in the journal Conservation Biology.

"This reinforces the urgency to conserve what is left and to try to reduce our impacts," said de Vos, who began the work while at the University of Zurich. "It was very, very different before humans entered the scene."

In absolute, albeit rough, terms the paper calculates a "normal background rate" of extinction of 0.1 extinctions per million species per year. That revises the figure of 1 extinction per million species per year that Pimm estimated in prior work in the 1990s. By contrast, the current extinction rate is more on the order of 100 extinctions per million species per year.

Orders of magnitude, rather than precise numbers are about the best any method can do for a global extinction rate, de Vos said. "That's just being honest about the uncertainty there is in these type of analyses."

From Fossils to Genetics

The new estimate improves markedly on prior ones mostly because it goes beyond the fossil record. Fossils are helpful sources of information, but their shortcomings include disproportionate representation of hard-bodied sea animals and the problem that they often only allow identification of the animal or plant's genus, but not its exact species.

What the fossils do show clearly is that apart from a few cataclysms over geological periodssuch as the one that eliminated the dinosaursbiodiversity has slowly increased.

The new study next examined evidence from the evolutionary family treesphylogeniesof numerous plant and animal species. Phylogenies, constructed by studying DNA, trace how groups of species have changed over time, adding new genetic lineages and losing unsuccessful ones. They provide rich details of how species have diversified over time.

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Extinctions during human era worse than thought