The passenger pigeon. The Tasmanian tiger. The Baiji, or Yangtze river dolphin. These rank among the best-known recent victims of what many scientists have declared the sixth mass extinction, as human actions are wiping out vertebrate animal species hundreds of times faster than they would otherwise disappear.
Up to now, public and scientific interest has focused on extinctions of species. In their new study, Gerardo Ceballos, senior researcher at the Institute of Ecology at the National Autonomous University of Mexico, and Paul Ehrlich, Bing Professor of Population Studies, Emeritus, in the Stanford School of Humanities and Sciences, have found that entire genera (the plural of “genus”) are vanishing as well, in what they call a “mutilation of the tree of life.”
“In the long term, we’re putting a big dent in the evolution of life on the planet,” Ceballos said. “But also, in this century, what we’re doing to the tree of life will cause a lot of suffering for humanity.”
“What we’re losing are our only known living companions in the entire universe,” said Ehrlich, who is also a senior fellow, emeritus, by courtesy, at the Stanford Woods Institute for the Environment.
Information on species’ conservation statuses from the International Union for the Conservation of Nature, Birdlife International, and other databases has improved in recent years, which allowed Ceballos and Ehrlich to assess extinction at the genus level. Drawing from those sources, the duo examined 5,400 genera of land-dwelling vertebrate animals, encompassing 34,600 species.
A total of 73 genera of land-dwelling vertebrates, Ceballos and Ehrlich found, have gone extinct since 1500 AD. Birds suffered the heaviest losses with 44 genus extinctions, followed in order by mammals, amphibians, and reptiles.
Based on the historic genus extinction rate among mammals—estimated for the authors by Anthony Barnosky, professor emeritus of integrative biology at UC Berkeley—the current rate of vertebrate genus extinction exceeds that of the last million years by 35 times.
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