Outside the Beltway

Evidence Of Human-Chimp Hybrids

Kate McMillan · Friday, May 19, 2006 · 3 comments

I know what you’re thinking – but no, it wasn’t obtained via search warrant *;

As we branched off on the evolutionary tree, our ancestors look to have made a messy break from those of chimpanzees. By comparing samples of chimp, gorilla and human DNA, scientists from MIT and Harvard say they see evidence of interspecies sex.

[…]

The geneticists rely on a molecular clock — a technique that estimates when two organisms shared a common ancestor by counting the number of genetic differences.

With more of the human and chimp genetic codes available, Reich examined several thousand stretches side by side.

To their surprise, they found some parts of the genetic code look like they diverged more recently than others — falling into a range of several million years. Alone it wasn’t enough to conclude intermixing occurred.

Their more shocking conclusion came from the X chromosome. There, our DNA seems to have diverged from chimps more than a million years later than DNA on other chromosomes.

In other creatures, sharing a similar X with another species can be a sign — a scarlet letter — pointing to interbreeding. This has to do with a connection between the X chromosome and infertility in hybrid offspring, said co-author Nick Patterson of the Broad Institute in Cambridge, Mass.

Most animals from different species can’t reproduce, he said. Some that are closely related can produce infertile offspring — as when donkeys and horses create mules. But in other cases some offspring might be fertile and not others, Patterson said. For reasons we don’t completely understand, he said, hybrid infertility in mammals seems to come from incompatible genes on the X chromosome.

Only hybrids with certain combinations of genes on the X would have the fertility necessary to pass them down, and that would dampen diversity in the X chromosome until the mixing stopped.

Patterson said these hybrid ape-creatures may have mated with each other or with members of either the human ancestral line or that of the chimps. They can’t say who ended up getting the hybrid genes.

The rest is here