LONDON — Humans' evolutionary split from their closest relatives, chimpanzees, may have been more complicated, taken longer and occurred more recently than previously thought, scientists said Wednesday.
A comparison of the genomes, or genetic codes, of the two species suggested that the initial split took place no more than 6.3 million years ago and probably less than 5.4 million years ago.
The process may have taken about 4 million years, and there could have been some inter-breeding before the final break.
"The study gave unexpected results about how we separated from our closest relatives, the chimpanzees," said David Reich of the Broad Institute and Harvard Medical School's Department of Genetics.
Instead of analyzing genetic differences, Reich and other researchers from the Massachusetts Institute of Technology and Broad Institute looked at variations in the degree of divergence between the two species in different regions of the genomes.
The analysis, published in the journal Nature, shows some regions in the human genome are older than others, which means they trace back to different times in the common ancestral population of the two species.
The youngest regions are unexpectedly recent, the researchers say, which means the separation was more recent than previously thought. "A hybridization event between human and chimpanzee ancestors could help explain both the wide range of divergence times ... as well as the relatively similar X chromosomes," Reich said.
Hybridization refers to the initial separation of two species, followed by interbreeding and then the final split.