Not a monkey's uncle exactly...

Hmm, turns out our closest relatives may be even closer than we think.

From the Washington Post:

When the ancestors of human beings and the ancestors of chimpanzees parted ways 6.3 million years ago, it was probably a very long goodbye. Some of their descendants may even have gone back for a final tryst.

That is the conclusion a group of scientists has reached, using a comparison of the genes of humans and their closest animal relatives to sketch a picture of human origins far more detailed than what fossil bones have revealed.

According to the new theory, chimps and humans shared a common apelike ancestor much more recently than was thought. Furthermore, when the two emerging species split from each other, it was not a clean break. Some members of the two groups seem to have interbred about 1.2 million years after they first diverged -- before going their separate ways for good.

I love stories like this, and not just because I find scientific discovery inherently fascinating, though that is a large part of it. As someone who loves puzzles, scientific inquiry sometimes seems like solving a Sudoku, though on a grander scale:

Humans have 23 pairs of chromosomes that contain about 30,000 genes. Each gene is made of strands of DNA "letters" in a specific order, and the letters can change, by mutation, over time. The rate at which changes occur is fairly constant -- and very slow.

As a result, genetic mutations can be used as a kind of evolutionary clock. The number of DNA differences between two species' versions of the same gene is an indication of how long the species have been separate -- how long since individuals were last interbreeding and sharing genes.

When Nick Patterson of MIT and his colleagues at the Broad Institute compared the genes of humans and chimps, they found that one of the chromosomes -- the female sex chromosome X -- was 1.2 million years younger than the others. It appeared the two species shared a common ancestor who gave them both their X chromosomes, and did so more recently than the ancestors who gave them all the other chromosomes.

The best explanation, the scientists think, is that ancient humans and chimps broke away from each other not once, but twice. The first time was more than 6.3 million years ago. The second time was at least a million years later.

What probably happened was that some of the evolving human ancestors bred with the evolving chimps. This was perhaps not as strange as it seems, for although there were some physical differences between the two groups, "the early humans must have looked pretty much like chimpanzees," said Mallet, the London geneticist.

Males have only one X chromosome, which is necessary for reproduction. As is often the case with hybrids, the male offspring from these unions would probably have been infertile.

But the females, which have two X chromosomes, would have been fertile. If some of those hybrid females then bred with proto-chimp males, some of their male offspring would have received a working X from the chimp side of the family. They would have been fertile -- and with them the hybrid line would have been off and reproducing on its own.

But as much as I love this kind of stuff, what really pops my cork is the image of all those IDiots out there whose veins must be ready to burst when reading such stories.

Though I'm not at all sure what Neal Horsely will make of all this. Perhaps he'll start cruising the zoo for dates?