“Let’s suppose you buy a book, we’re used to getting books where the cover’s on right, the pages are in order, and they tell a continuous story. But imagine a publisher that duplicated his pages, dropped some pages, changed the order of the pages. That’s what happens in the human genome. That’s copy number variation.”
This form of mutation turns out to appear with surprising frequency in the human genetic text. Wigler’s group first glimpsed the phenomenon in cancer cells, but his hunch was that similar “publishing” errors might also play a role in diseases like autism. Sure enough, when the researchers examined the genomes of people with autism, they often found weird, large-scale duplications or deletions of DNA—mutations not present in the mother or father. The fact that they were not inherited strongly suggested that they were recent corruptions of the genetic text, almost certainly arising in the sperm or egg cells of the parents.
“The evolutionary twist on this whole story, is that our genome is really set up to fail, in the sense that we’re prone to delete and duplicate. The flip side of it is that that selective disadvantage is offset by the emergence of novel genes that have conferred an advantage to us cognitively.”