Human beings have 23 pairs of chromosomes but our closest cousins the chimpanzees have 24 pairs. This was at one time a puzzle because if, as the theory of evolution says, both species share a common ancestor, how could it be that in the relatively short time after the human and chimp lines separated about six million years ago, humans could have lost an entire chromosome, with all the genetic information it contained, and yet survived as a species?

We now know that what happened was that a chromosome was not lost but that two chromosomes fused together end-to-end, thus preserving all the genetic information. This turns out to be not as uncommon as one might think, and happens from time to time even now. There are people walking around now with just 22 chromosomes because of later fusions. Science reporter Carl Zimmer has a nice article explaining how it happens.

A comparison of the human, chimpanzee, and gorilla genomes confirms that the ancestors of gorillas branched off from the ancestors of chimpanzees and humans about ten million years ago. Humans and chimpanzees then branched apart later. A comparison between all three species provides a clearer picture of what our chromosomes looked like before they fused, and how they’ve changed since.

In the process, he and biologist Nick Matzke got into a discussion with creationist David Klinghoffer of the Discovery Institute, which had a post on their website about how there was evidence against this fusion explanation. Matzke challenged this assertion and Zimmer asked Klinghoffer to reveal this evidence. The Discovery people keep asking Zimmer to buy a book where this argument resides or to engage in an extended debate instead of simply citing the paper that supposedly buttresses their argument.

But someone who had read the book reveals what this ‘evidence’ is. It is the usual tactic of ‘quote-mining’, where the creationists take a rhetorical question that the authors of a real scientific paper pose as a prelude to setting up their explanations, and present that question as if it were a conclusive statement of bafflement. I discussed this dishonest creationist tactic earlier in the context of research on the origins of life, using a typically pointed cartoon from Jesus and Mo as an illustration.

The trouble for creationists is that Zimmer knows what he is talking about and the runaround that they try to give him to avoid answering the question is fun to read.