Our ancestors made the evolutionary split with gorillas around 10-million years ago, but we still share a remarkable number of genes with the great ape, according to a ground-breaking study published on Wednesday.
A worldwide consortium of scientists sequenced the genome of the western lowland gorilla and compared more than 11Â 000 of its key genes with those of modern humans, Homo sapiens, and chimpanzees.
Gorillas diverged from the human-chimp lineage around 10-million years ago, and around 4-million years later, Homo and chimps emerged on their own as a separate species, a figure that tallies with fossil evidence.
The comparison also overturns convictions about similarities between the major primates, the investigators said.
As expected, humans and chimps shared the most genes, they found.
But 15% of the human genome is closer to the gorilla genome than it is to the chimpanzee — and 15% of the chimp genome is closer to the gorilla genome than it is to human.
Evolutionary divergence
“Our most significant findings reveal not only differences between the species reflecting millions of years of evolutionary divergence but also similarities in parallel changes over time since their common ancestor,” said Chris Tyler-Smith from Britain’s Wellcome Trust Sanger Institute.
“We found that gorillas share many parallel genetic changes with humans — including the evolution of our hearing.
“Scientists had suggested that the rapid evolution of human hearing genes was linked to the evolution of language. Our results cast doubt on this, as hearing genes have evolved in gorillas at a similar rate to those in humans.”
Gorillas themselves began to split into two groups, the eastern lowland gorilla and the western lowland gorilla, about a million years ago.
The study throws cold water over the notion that when primate species diverged, this happened rather abruptly, over a relatively short period.
Instead, the process was longer and very gradual.
Kissing cousins
There was probably a fair amount of “gene flow”, or inter-breeding between slightly different genetic strains, both before gorillas split from the other apes and before gorillas themselves diverged into two species.
There could well be a parallel in the split between chimps and bonobos, or between modern humans and Neanderthals, say the authors.
A new theory about Neanderthals is that they were more than kissing cousins — Homo sapiens occasionally interbred with them and incorporated some of their genes into modern humans.
The Neanderthals themselves died out as a separate species around 40Â 000 years ago, wiped out either by a changing climate or by Homo sapiens himself, according to some hypotheses.
The DNA sample came from a female western lowland gorilla named Kamilah.
After thriving for millions of years, gorillas survive today in just a few isolated, badly endangered populations in central Africa, their numbers diminished by hunting and habitat loss.
“As well as teaching us about human evolution, the study of the great apes connects us to a time when our existence was more tenuous, and in doing so, highlights the importance of protecting and conserving these remarkable species,” says the study. — AFP