Face Blindness

Us humans seem to have a specialized mental mechanism for identifying faces. It’s pretty easy to see that could have been favored by selection for a long, long time.

In 2006, Ingo Kennerknecht and associates published a study indicating that about 2.5% of people in Germany had a hereditary, congenital form of prosopagnosia (face blindness). Looking at the pattern of occurrence in families, they concluded that it is inherited as an autosomal dominant.

That’s strange. Once in a while, a recessive allele with negative effects in homozygotes can get that common – for example, malaria defenses like sickle-cell. In a case like that, big disadvantage in homozygotes are balanced by smaller (still sizeable) advantages in heterozygotes. The frequency of the sickle-cell allele stabilizes at an intermediate frequency, say 10%.

But here, the negative effects are in heterozygotes. There’s no way that they could be balanced by advantages in homozygotes, which are much rarer.

So how can prosopagnosia exist at such a high frequency? Well, maybe it’s like red-green color-blindness. The mutation rate for errors in the genes coding red and green opsins
is unusually high, due to illegitimate recombination. If you assume that the high frequency we see today in Europeans is a product of mutation accumulation due to relaxed selection since the dawn of agriculture some ten thousand years ago, it’s the highest mutation rate known, around 2 x 10-4 per generation, higher even that of dystrophin (the longest gene). It seems that the fitness loss due to red-green color blindness isn’t too large, at least in some societies. It’s hard for me to believe that face blindness matters so little, but maybe.

The next thought is that the allele for prosopagnosia is linked to some driving gene, something like the t-haplotype in mice. The t-haplotype cheats, so that 90% of a male carrier’s offspring carry the t-haplotype, instead of the usual 50%. Homozygous males are sterile, which ( along with other factors) keeps the t-allele from going to fixation. People have looked for transmission distortion in the human genome, but there are no definitive results, as far as I know.

The third explanation is that this research is just wrong..

Interesting that the authors don’t seem to have noticed how strange their claim really is.

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39 Responses to Face Blindness

  1. Not EO Wilson says:

    The fourth explanation is that having that frequency of prosopagnisics is group-scale adaptive.

    “We demonstrate that the evolution of facial recognition in wasps is associated with specialized face-learning abilities. Polistes fuscatus can differentiate among normal wasp face images more rapidly and accurately than nonface images or manipulated faces. A close relative lacking facial recognition, Polistes metricus, however, lacks specialized face learning.
    […]
    Convergence toward face specialization in distant taxa as well as divergence among closely related taxa with different recognition behavior suggests that specialized cognition is surprisingly labile and may be adaptively shaped by species-specific selective pressures such as face recognition.”
    https://www.sciencemag.org/content/334/6060/1272

    “In a second example, discovered in the fire ant Solenopsis invicta, new variants of the major gene Gp-9 greatly reduce or remove the ability of workers to recognize aliens from other colonies, as well as the ability to discriminate among fertile queens. The resulting ‘microgyne’ strain forms dense, continuous supercolonies that have spread over much of the species range in the southern United States.”
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279739/

    “Our main findings were that homosexual males have better face recognition memory than both heterosexual males and homosexual women.”
    http://www.tandfonline.com/doi/abs/10.1080/13576500903503759

    • gcochran9 says:

      That’s just stupid.

      • Not EO Wilson says:

        It happens with the other eusocials, so why would humans be a magical exception?

        • gcochran9 says:

          Humans are not eusocial. Queen Elizabeth does not have hundreds of thousands of babies every year.

          Let us imagine that not being able to recognize faces reduces individual fitness, which seems pretty likely to me. Let us assume having a fair number of face-blind individuals somehow aids the fitness of a German tribe, village, town, or possibly the entire Reich. Everyone one of those possibilities sounds absolutely ridiculous, but let us suppose it.

          Ok then: with simple dominant inheritance, the frequency of the prosopagnosia trait goes down. And then it goes down again. It goes down in every generation. Even if a critical number of face-blind people somehow helped Frederick the Great steal Silesia, the frequency still goes down. Faster, in fact, since that meant absorbing a lot of Poles.

          Even if Germans benefited from that, the benefits were spread widely, not concentrated on those carrying the hypothetical prosopagnosia gene, who bear all the costs. So the frequency goes down, down, down down, down.

          The only scenario in which something like this works is if we have a bunch of small tribes that spend most of their time fighting with their neighbors. And when they win, they exterminate those neighbors, including the women. Although the frequency of the altruistic gene is still dropping, on average, in every group, the groups with the higher frequencies tend to beat their neighbors and then the group expands (into more little groups that also fight with each other and refrain from interbreeding).

          You need lots of and lots of ongoing extermination, groups wiping out rival groups. Not just fighting them – wiping them out. In other species, this might mean losing out to exterior foes – some sort of bee predator taking out a hive that doesn’t fight back enough – but with humans, the only suitable foes are other humans.

          Might have happened once upon a time, although the bit about killing almost all the captive women seems unlikely. Have the past few thousand years been like this? No.

          Enough already. There are way, way, way too many stupid people around nowadays.

      • JayMan says:

        Ah I love this place! 🙂

      • misdreavus says:

        Do you ever get tired of having to explain basic facts about nature to people, over and over and over again?

        It’s a pretty thankless job, but congratulations to you, for decades of tireless dedication toward the Sisyphean labor of slapping a fool upside the head. I don’t think I would have lasted anywhere near that long.

      • misdreavus says:

        “The fourth explanation is that having that frequency of prosopagnisics is group-scale adaptive.”

        How ’bout this: NO.

      • Not EO Wilson says:

        “Humans are not eusocial. Queen Elizabeth does not have hundreds of thousands of babies every year.”

        I’ve never heard human eusociality described in those terms (or rodent eusociality, or shrimp eusociality, etc.). I was under the impression you were open to a Jaynesian view of recent human evolution:
        http://www.2blowhards.com/archives/2009/01/a_week_with_gre_2.html

        Isn’t eusocial genetic material shared between ridiculously distant taxa evidence that many species are already primed for it (Wilson thinks so).

        For example, prosopagnosia is common in autism:
        “Identification of eusocial behaviors in a background strain for genetic animal models of autism”
        https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3264663/

        PS: Better?

  2. misreavus says:

    “Isn’t eusocial genetic material shared between ridiculously distant taxa evidence that many species are already primed for it (Wilson thinks so).”

    I’m not even sure what this is supposed to mean. Umm… what?

  3. MikeP says:

    If I remember correctly, Wilson’s idea is that nest making is a preadaptation of eusociality and, to the extent that nest making and the behaviors that go along with it are broadly distributed among taxa, a predisposition to evolve eusociality is broadly distributed.

  4. Temporal Shift? says:

    I wonder if the selection pressure for face-blindness has shifted significantly over the course of history (which we should be able to test for, if we have a large sample of genetic material from deceased Germans, which is probably difficult to acquire). When in the jungle, telling the difference between Bob, your worst enemy who is willing to shoot you as an ‘accident’, and Charlie, who is your strongest supporter in group debates, taking longer than a tenth of a second to figure out which one it is seems like it could significantly negatively impact the number of descendents you have.

    But in post-medieval Germany? There are way less combat situations like that, and most social situations involve enough context that faces are helpful but not necessary. “I’m at home and there’s a woman -> that woman is probably my wife.”

    The largest group of face-blind people I know is the staff at a critical thinking charity I’m familiar with; about a quarter of them are significantly face-blind, and now tell people about Bayes’ Rule and correct reasoning from evidence as a living. It’s possible that’s a fluke (a quarter is 2 out of 8), but it’s also possible that having to constantly figure things out from limited evidence strengthens cognitive muscles that are much more useful in the industrial environment than ancestral environments. (2.5% seems high enough that I suspect we would need to have positive selection pressure to explain this as a genetic effect. It’s not obvious to me how to test for this sort of reasoning from limited evidence, but this might be something you could ask face-blind people about and get reasonable information. It also doesn’t seem likely to me that you can explain 2.5% from the ~8 generations since industrial society started; this would need to be adaptive in medieval environments too, which seems less likely to me.)

    The other effects I can think of after a few minutes thought: face-blind people are more likely to offend others than face-sighted people (not recognizing someone who recognized you is problematic), probably less able to be hypocritical (if you’re never quite sure who you’re talking to, then you might be more careful about that sort of thing), probably better at listening (to recognize people by their voices), are probably more deliberate about their relationships with others, and probably have more affairs (but I get the impression that this isn’t a reproductive positive in situations where children are food-limited rather than sex-limited).

  5. Richard Sharpe says:

    But here, the negative effects are in heterozygotes. There’s no way that they could be balanced by advantages in homozygotes, which are much rarer.

    If I haven’t screwed up the math, about 40 times rarer. That advantage would have to be enormous.

  6. RS says:

    > But in post-medieval Germany? There are way less combat situations like that, and most social situations involve enough context that faces are helpful but not necessary. “I’m at home and there’s a woman -> that woman is probably my wife.”

    This seems pretty weak to me.

    > but it’s also possible that having to constantly figure things out from limited evidence strengthens cognitive muscles that are much more useful in the industrial environment than ancestral environments.

    That is one weird thought, but I think it makes a fair amount of sense. It wouldn’t be the first time nature has been weird like that.

    > It also doesn’t seem likely to me that you can explain 2.5% from the ~8 generations since industrial society started; this would need to be adaptive in medieval environments too, which seems less likely to me.

    A lot of people think Europe’s been getting somewhat wealthier per capita for 500 years. It may, then, have been getting more societally complex and less peasant over that whole period. And really, I have seen just about no art of real interest from North Europe before 700-800 — the ur-ancient pre-agricultural cave paintings in France have noticeably more grace, as do very old Jomon artifacts — and glorious art does not seem widespread there until 1000. There is a large and rather rapid change which I think is likely to be substantially biological.

    So I can basically imagine N-Europe getting more complex not just after 1750, but also to some extent during much or most of 600-1750.

  7. Melykin says:

    Calling people stupid is rude and mean spirited. It really puts me off this blog. Just saying.

    • R. Jones says:

      +1

    • gcochran9 says:

      That guy was stupid, of course, but he was also obscene and insulting, which is why I banned him instantly (and removed the insulting comment). But let us suppose that he had been the same fountain of nonsense, yet polite? After a while, after a couple of warnings (which never work) I would have banned him anyway.

      If you want to read a lot of nonsense, go somewhere else. You’ll find all you want.

    • dave chamberlin says:

      The internet ain’t the real world. At first I thought the same thing you did but then I found the blogs run by really nice people have the comment section filled with nonsense. Rudeness isn’t necessary in the real world and I hate it as much as you do but over here in the series of tubes people seem far more inclined to jump off their garage roof on to a table or to light themselves on fire. We need the slap police to just keep them away or else we are all neck deep in drivel.

  8. juicehunter99 says:

    Maybe its a venereal disease…Face blindness makes women more likely to become prostitutes and so spread the disease……just joking 🙂

  9. Anthony says:

    My first instinct is that face-blindness isn’t perhaps as much a disadvantage as you might think, especially in a pre-industrial but relatively pacified agricultural society with very little physical mobility and some tradition of arranged marriages.

  10. hbd chick says:

    prosopagnosia is a spectrum disorder. i have a mild case (typically don’t recognize someone from work out of context, like at the supermarket, but i do recognize the d.h. everywhere), whereas some people have severe cases (don’t recognize themselves in a mirror!).

    don’t know what, if any, difference that makes.

    • observer says:

      I seem to recall that Von Neumann had a mild case of prosopagnosia. This made me wonder whether it was a case of pleiotropy (or else linkage to a beneficial gene) wherein other mental functions were improved at the cost of impaired facial recognition. Since hbd chick is pretty smart as well, that doubles the support for my theory. I wonder if any intelligence testing has been done on prosopagnosics. Mild impairment sounds fairly harmless in a village/small town context. Of course, face ‘myopia” and face blindness could also have different origins.

      I suspect Mr. Cochran has considered and rejected this idea, since the explanations he proposes are more complex. Still an interesting problem.

      • JLikens says:

        As a potential counterpoint, I believe the incidence of prosopagnosia is elevated among those with Aspergers Syndrome, who are less intelligent on average.

  11. Pingback: linkfest – 05/26/13 | hbd* chick

  12. Purple Pie Pete says:

    Explanation three is most likely the correct one. Kennerknecht’s pedigrees suggest an autosomal dominant gene is responsible, but those pedigrees were created by asking a self-identified prosopagnosic to report which of his relatives were and were not prosopagnosic. That’s not a reliable way to create pedigrees. They should have carried out behavioral testing with each individual. Prosopagnosia definitely runs in families, but I haven’t seen convincing data indicating it is caused by an autosomal dominant. It may be a complex genetic disorder (which would still be interesting). It’s worth mentioning too that many prosopagnosics are unaware of any family history of prosopagnosia (50%?)

  13. g2-337af867fe9cd20258bdbc586fbefd0d says:

    Prosopagnosis is at the mild extreme of the autism spectrum of diseases. This thing seems to hit an ever larger proportion of children. I think Cochran’s third possibility is improbable. Something IS happening. What and why?

  14. tyrionlannister69 says:

    Socially relevant facial information is processed separately from facial information leading to individual face recognition. In recent years functional imaging has identified a network of distinct occipitotemporal cortex areas for the processing of these two kinds of information. Functionally it is not clear at which processing level the “social” and the “recognition” pathways diverge. In some studies was tested the perception of attractiveness (a cue of prime social importance) and distinctiveness (a facial feature related to recognition) in people with congenital prosopagnosia, and their ratings of attractiveness were highly consistent with controls, but their distinctiveness ratings showed random patterns. This dissociation of normal attractiveness processing and impaired distinctiveness processing in prosopagnosia should help to specifies the nature of the impairment in this condition while shedding light on the functional architecture of normal face processing.

  15. frost says:

    At some point I could have sworn that GC made a post asking for readers to give a fact he didn’t know. I just looked back thru February and can’t find it. The following is off topic here but maybe someone will find it interesting.

    http://en.wikipedia.org/wiki/Hemocyanin

    Yep, there are some animals that do not have red blood based on iron binding of oxygen. Some (and only some) animals in the molusca & arthropoda have oxygen transport based on copper and have blue blood!

    According to WP “Most hemocyanins bind with oxygen non-cooperatively and are roughly one-fourth as efficient as hemoglobin at transporting oxygen per amount of blood.” You would think that would be a big disadvantage. Even tho most animals that utilize hemocyanin are sea dwellers and hence don’t have to bear the extra weight of 4x the blue blood you would still think that the extra energy to pump the larger volume of blood would be a significant disadvantage. However, the WP article later gives examples where the oxygen transport via hemocyanin was competitive with hemoglobin.

    • gcochran9 says:

      It was on April 1st, of course. Naturally I already knew about hemocyanin. That’s nothing: there are Antarctic fish that simply do without an oxygen-binding protein.

      • frost says:

        Thanks for giving us a chance to play the game; it gives us something to aspire to.

        The other thing I find astounding is the discordance within phyla. I would have thought that oxygen transport would have been settled very early but evidently not. Hemocyanin may have evolved several times…but in response to what pressure?

  16. Face blindness is disabling. 2.5% sounds very high. They also find it in Hong Kong Chinese at a similar rate of 1.88%. None of these are proper epidemiological samples. http://www.ncbi.nlm.nih.gov/pubmed/18925678 Duchaine B. doubts their conclusions.
    THEY DO NOT ADMINISTER A TEST, JUST A QUESTIONNAIRE. They say there is no single diagnostic test with sufficient sensitivity and specificity. I think we cannot draw too many conclusions from their prevalence estimates.

    • melendwyr says:

      “They say there is no single diagnostic test with sufficient sensitivity and specificity.”

      Why can’t you just show unfamiliar faces to people, then ask them to pick out the ones they were shown from a collection of even more unfamiliar faces? Seriously, please educate me – is there something special about prosopagnosia that would render that sort of test ineffective?

  17. Pingback: Grab-Bag | Mitchell Powell's Blog

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