Humans are driving loss of entire branches of ‘Tree of Life,’ warn scientists

A study published in the Proceedings of the National Academy of Sciences (PNAS), on Monday (September 18), said that humans are driving the loss of entire branches of the “Tree of Life,” warning of the threat of a sixth mass extinction.

What makes this study unique is that it looks beyond just the examination of the loss of a species and rather examines the extinction of entire genera. The genus is essentially a biological classification which lies between the rank of species and that of family.

What did the study find?

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The study is largely based on the species listed as extinct by the International Union for Conservation of Nature (IUCN) and focuses on vertebrate species (excluding fish), for which more data is available.

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The researchers found that out of some 5,400 genera – which comprises some 34,600 species – 73 had become extinct in the last 500 years with most of them disappearing in the last two centuries. This was also compared with the extinction rate estimated from the fossil record over the very long term.

Explaining the severity of the situation, the co-author of the study and professor at the National Autonomous University of Mexico, Gerardo Ceballos told news agency AFP, “Based on the extinction rate in the previous million years we would have expected to lose two genera. But we lost 73.”

The study also gave a rough estimate – since not all species are known and the fossil record remains incomplete – that this process should have taken at least 18,000 years, not 500. “What is at stake is the future of mankind,” Ceballos said.

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Impact of human activity

Scientists have attributed this rapid change and loss to human activities like the destruction of habitats for crops or infrastructure, as well as overfishing, hunting and so on. Ceballos also warned how the loss of one genus can have consequences for an entire ecosystem.

“It is a really significant contribution, I think the first time anyone has attempted to assess modern extinction rates at a level above the species,” Robert Cowie, a biologist at the University of Hawaii who was not involved in the study, told AFP about the research.

“As such it really demonstrates the loss of entire branches of the Tree of Life,” a representation of living things first developed by Charles Darwin.

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The study shows that “we aren’t just trimming terminal twigs, but rather are taking a chainsaw to get rid of big branches,” Anthony Barnosky, professor emeritus at the University of California, told AFP.

Scientists broadly define a mass extinction as the loss of 75 per cent of species over a short period of time and by that “arbitrary,” definition a sixth mass extinction has not yet occurred, said Cowie, but warned that if “species continue to go extinct at the current rate (or faster), then it will happen.”

(With inputs from agencies)

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