Humans get a new cousin

And then there were eight. A team of researchers has identified a previously unrecognised species of orangutan, adding an extra member to the great ape family.

The discovery means that now humans have seven close relatives: two species of gorilla, plus chimpanzees, bonobos and three orangutans.

The new species, formally named Pongo tapanuliensis in a paper published in the journal Current Biology, is critically endangered and comprises a single colony of fewer than 800 individuals living in Batang Toru on the island of Sumatra.

An international team of researchers from 34 institutions, led by anthropologist Alexander Nater of the University of Zurich in Switzerland, pursued two lines of evidence to determine if the ape colony was different enough from the two already acknowledged orangutan species – known as the Bornean and Sumatran – to be defined as a third.

Firstly, they used the skull of a specimen killed during what they describe as a “human-animal conflict” to compare head and jaw characteristics with those of 33 adult male orangutans. In so doing, they found “consistent differences” in skull and tooth size between the Batang Toru ape and the others.

After that, they analysed 37 orangutan genomes. This revealed that not only was P. tapanuliensis a separate species, but also a very ancient one.

The analysis revealed that the new species split away from the others around 3.3 million years ago. The Bornean and Sumatran species, in contrast, split from each other only around 674,000 years ago.

One of the researchers, biological anthropologist Colin Groves from the Australian National University in Canberra hails the team’s achievement.

“It’s a very significant discovery,” he says. “The orangutan is one of our closest living relatives and we’ve now found there is more diversity within orangutans than we knew.”