Study finds chimps, humans split 4m years ago
3:03 PM February 24
A new study has found chimpanzees and humans split from a common ancestor just four million years ago - a much shorter time than current estimates of five million to seven million years ago.
The researchers compared the DNA of chimpanzees, humans and our next-closest ancestor, the gorilla, as well as orang-utans.
They used a well known type of calculation that had not been previously applied to genetics to come up with their own "molecular clock" estimate of when humans became uniquely human.
"Assuming orang-utan divergence 18 million years ago, speciation time of human and chimpanzee is consistently around 4 million years ago," they wrote in their study, published in the Public Library of Science journal PLoS Genetics.
The theory of a molecular clock is based on the premise that all DNA mutates at a certain rate. It is not always a steady rate but it evens out over the millennia and can be used to track evolution.
Experts agree that humans split off from a common ancestor with chimpanzees several million years ago and that gorillas and orang-utans split off much earlier.
But it is difficult to date precisely when, although most recent studies have put the date at somewhere around five million to seven million years ago.
Asger Hobolth of North Carolina State University in the United States, and colleagues from the University of Aarhus in Denmark and the University of Oxford in Britain, looked at four regions of the human, chimpanzee, and gorilla genomes.
They used a statistical technique called the hidden Markov model, developed in the 1960s and originally applied to speech recognition.
What they found may contradict some other recent research. They found evidence that it took only 400,000 years for humans to become a separate species from the common chimp-human ancestor.
Just last May, David Reich of the Broad Institute at the Massachusetts Institute of Technology and Harvard Medical School's Department of Genetics found evidence that the split probably took four million years to occur, although his team put the final divergence at just 5.4 million years ago.
"I don't think it really contradicts our paper," Dr Reich said via email.
"We were focusing on a maximum time for the common ancestor of humans and chimpanzees, while they were focusing on a best estimate."
Experts have long known that humans and chimpanzees share much DNA, and are in fact 96 per cent identical on the genetic level.
One year ago, Soojin Yi and colleagues at the Georgia Institute of Technology said they found genetic evidence that chimpanzees may be more closely related to humans than to gorillas and orang-utans.
Their look at the molecular clock showed humans evolved one unique trait just one million years ago - our longer life span and our long childhood that means humans reach sexual maturity very late in life compared to other animals.
- Reuters Source: Reuters
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