Mutants among us

Prosopagnosia, or face blindness, affects a surprisingly large fraction (few percent) of the population. Those who suffer from it have difficulty in distinguishing human faces, except by conscious effort (recalling particular features, or contextual clues). Preliminary evidence is that (a) we have a specialized module in our brains for face recognition and (b) there are one or more alleles (gene variants) which disable this function to various degrees.

How could these alleles survive selection? One would guess that face blindness is an evolutionary handicap, at least to some degree (although perhaps less so in small hunter gatherer groups, or in theoretical physics ;-). Is there a compensating advantage provided by the mutation?

It's fascinating to consider how many other strange cognitive mutations are present in our population at the percent (or fraction of percent level). Memory? Musical ability? Specialized mathematical ability (e.g., visualizing geometrical shapes, or a "feel" for magnitudes of quantities, or lightning calculation)?

I suspect we'll find more and more of these, and their associated alleles, as time goes by. See GNXP.com for more discussion and references.

It just occurred to me that there are likely dozens of readers of this blog who have prosopagnosia. Would anyone care to share their (anonymous) comments on how they adjust to the condition, and when they noticed having it?

NYTimes: Dr. Sellers, a professor of English at Hope College in Holland, Mich., has a disorder called prosopagnosia, or face blindness, and she has had it since birth. “I see faces that are human,” she said, “but they all look more or less the same. It’s like looking at a bunch of golden retrievers: some may seem a little older or smaller or bigger, but essentially they all look alike.”

Face blindness can be a rare result of a stroke or a brain injury, but a study published in the July issue of The American Journal of Medical Genetics Part A is the first report of the prevalence of a congenital or developmental form of the disorder.

The researchers say the phenomenon is much more common than previously believed: they found that 2.47 percent of 689 randomly selected students in Münster, Germany, had the disorder.

Dr. Thomas Grüter, a co-author of the paper, said there were reasons to believe that the condition was equally common in other populations. “First,” he said, “our population was not selected in terms of cognition deficits. And second, a study done by Harvard University with a different diagnostic approach yielded very similar figures.”

Dr. Grüter is himself prosopagnosic. His wife and co-author, Dr. Martina Grüter of the Institute for Human Genetics at the University of Münster, did not realize he was face blind until she had known him more than 20 years. The reason, she says, is he was so good at compensating for his deficits.

“How do you recognize a face?” she asked. “For most people, this is a silly question. You just do. But people who have prosopagnosia can tell you exactly why they recognize a person. Thomas consciously looks for the details that others notice unconsciously.”