Thu, 21 Mar 2013 11:00 CDT
© F. Demeter
A new genetic analysis suggests that humans left Africa no earlier than 95,000 years ago, pushing the date of that migration back more than 100,000 years.
Our early human ancestors may have left Africa more recently than thought, between 62,000 and 95,000 years ago, suggests a new analysis of genetic material from fossil skeletons.
The new findings are in line with earlier estimates, but contradict a more recent study that put humans' first exodus from Africa
least 200,000 years ago.
The new results "agree with what we know from archaeology," said study co-author Alissa Mittnik, a biologist at University of Tübingen, in Germany.
Exactly when the first humans emerged from Africa to colonize the world has been a topic of heated debate.
All of the estimates hinge on one number: the gene mutation rates
. By knowing how often genes change, and then counting up the number of genetic differences between different species or groups of people, scientists can create a "molecular clock" to decipher how long ago they shared a common ancestor.
Early studies used genetic differences in mitochondrial DNA
- genetic material inside the cells' energy-making structures that gets passed on from mother to child - between chimpanzees and humans.
But since that technique is based on the number of mutations divided by the time since the two shared a common ancestor, it requires an estimate of when the common ancestor of chimpanzees and humans
Newer research estimated the mutation rate in modern human families based on DNA from the nucleus, which involved another way of getting at the common ancestor timing. That method suggested humans were racking up genetic mutations at half the rate - meaning to reach the genetic differences we see today humans would've had to leave Africa more than 200,000 years ago.