Researchers examining extinction of large mammals as humans spread across the world see worrying trend

This article is more than 2 years old

This article is more than 2 years old

The cow could be left as the biggest land mammal on Earth in a few centuries, according to a new study that examines the extinction of large mammals as humans spread around the world.

The spread of hominims – early humans and related species such as Neanderthals – from Africa thousands of years ago coincided with the extinction of megafauna such as the mammoth, the sabre-toothed tiger and the glyptodon, an armadillo-like creature the size of a car.

“There is a very clear pattern of size-biased extinction that follows the migration of hominims out of Africa,” the study’s lead author, Felisa Smith, of the University of New Mexico, said of the study published in the journal Science on Thursday.

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Humans apparently targeted big species for meat, while smaller creatures such as rodents escaped, according the report, which examined trends over 125,000 years.

In North America, for instance, the mean body mass of land-based mammals has shrunk to 7.6kg (17lb) from 98kg after humans arrived.

If the trend continues “the largest mammal on Earth in a few hundred years may well be a domestic cow at about 900kg”, the researchers wrote. That would mean the loss of elephants, giraffes and hippos. In March, the world’s last male northern white rhino died in Kenya.

But other research casts doubt on a continued shrinking of mammals, partly because of conservation efforts to stave off threats to wildlife such as climate change, loss of forest habitats, pollution and expanding cities.

The International Union for Conservation of Nature chief scientist, Thomas Brooks, who was not involved in the study, said the projection of ever smaller mammals was “doom and gloom”.

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“Happily, I don’t think it’s very likely,” he said, adding that other research suggests large animals such as elephants are more likely to benefit in protected areas than smaller ones.

And a red list of threatened species, maintained by the union, also lists some wild mammals roughly the size of a cow – such as the African buffalo or the brown bear – as unendangered.

The Science study also excludes marine mammals such as the blue whale, the largest creature that has ever existed. It is listed as endangered on the red list but the populations are rising after a moratorium on hunting.

Smith said “my optimist hat would like to say that it’s not going to happen because we love elephants”. But she said populations of large land mammals were falling and “declining population is the trajectory to extinction”.