The evolutionary split between humans and our nearest evolutionary cousins, chimpanzees, may have occurred more recently than we thought, according to a new comparison of the respective genetic sequences. What's more, it might have been a messy divorce rather than a clean break — leading to the controversial theory that our two sets of ancestors may have interbred many thousands of years after first parting company.
The discovery also casts doubt on the status of fossils that were thought to represent the first flowering of the human branch of the evolutionary tree — but which now may have to be reclassified as coming from a time before our split with the rest of the apes.
Previous estimates put the split at as much as 7 million years ago — meaning that Toumaï, a fossil dating from at least 6.5 million years ago in Chad and assigned to the species Sahelanthropus tchadensis, was hailed as the earliest-known member of the line that gave rise to modern humans.
But researchers led by David Reich of Harvard Medical School in Boston, Massachusetts, now calculate that the split may have occurred no more than 6.3 million years ago, and possibly as recently as 5.4 million. That would make Toumaï older than the time of the split.
But the story is not simple, Reich and his team explain in their study, published online in Nature1. Different sections of the genome differ by different amounts, suggesting that they parted ways at different times. The divorce period between the two species, the data suggest, could have lasted a million years.
The region bearing the most similarity is the X chromosome. This is exactly what one might expect if the two lineages had continued to interbreed after first starting to separate.
If such a hybrid population really did exist, the question remains as to whether it died out, or whether modern humans or chimpanzees (or both) are its descendants. It's very difficult to say, admits Reich. "The fossil data suggest — very tenuously — that it may have been humans who are descended from the hybrid population."
As I've found out, there's a lot of weird stuff in the human genome, so something like this, while a shock, isn't a surprise. I'm not a monkey's uncle, but if they're our kissin kin, then I am a chimpanzee's aunt. And we're all children of a broken home too. If I was to go all sociological, that might explain something about both chimpanzee and human behaviour.
Whether the hypothesis is true or not, for reasons which have nothing to do with kinship, but my studies on the nature of Intelligence, I've come to the conclusion that the Great Ape Declaration has much to commend it. Worth thinking seriously about, anyway.
We demand the extension of the community of equals to include all great apes: human beings, chimpanzees, bonobos, gorillas and orang-utans.I'm not too sure about the second point, but the first and third are undeniable, based on scientific research on Bonibos, Forest Chimps and Gorillas. The others I'm less certain of, but again, it's worth looking at. Hard. And without the usual ridicule and summary dismissal as a patent absurdity.
The community of equals is the moral community within which we accept certain basic moral principles or rights as governing our relations with each other and enforceable at law. Among these principles or rights are the following:
1. The Right to Life
The lives of members of the community of equals are to be protected. Members of the community of equals may not be killed except in very strictly defined circumstances, for example, self-defense.
2. The Protection of Individual Liberty
Members of the community of equals are not to be arbitrarily deprived of their liberty; if they should be imprisoned without due legal process, they have the right to immediate release. The detention of those who havenot been convicted of any crime, or of those who are not criminally liable, should be allowed only where it can be shown to be for their own good, or necessary to protect the public from a member of the community who wouldclearly be a danger to others if at liberty. In such cases, members of the community of equals must have the right to appeal, either directly or, if they lack the relevant capacity, through an advocate, to a judicial tribunal.
3. The Prohibition of Torture
The deliberate infliction of severe pain on a member of the community of equals, either wantonly or for an alleged benefit to others, is regarded as torture, and is wrong.