Posted by: Chris | August 27, 2009

An Addendum

Writing the post about the Fresno blog (which doesn’t seem to update so frequently) reminded me of something Andrew linked to not too long ago. Basically, the guy offers up a handful of speculative “just-so” stories to explain how homosexuality could have maintained itself evolutionarily through a variety of increasingly bizarre circumstances:

  • the gay uncle theory, wherein homosexuals increase the viability of their nephews/nieces (with whom they only share 25% of their genome) through increased parental care and thus increase their own selective potential
  • the male-alliance theory, in which homosexual relations facilitates alliances between competing males, increasing survival and boosting fecundity (not unlike bonobos).
  • the sneaky fucker theory, in which homosexuality makes men less threatening to women and in turn increases their chances of mating

All of these explanations are pretty ridiculous/unlikely natural selective explanations for a very obviously maladaptive trait. Lest you think they are the product of Jesse Bering, quack, the article attributes the first to E.O. Wilson and the last to John Maynard Keynes, while a quick google search has Richard Dawkins endorsing all three in the course of explaining how a “gay gene” could have survived selective pressures. Not only is all this self-defeatingly silly, it is also completely unnecessary. We have accepted the genetic persistence of all kinds maladaptive traits. Nobody wonders, for example, what selective benefits midgets have.


But I didn’t write this post to solely deride acclaimed biologists from our lofty perch here. I am writing because this offers a good example of how reflexively adaptionist explanations tend to miss more interesting biological questions. Last year in genetics we read an interesting paper by Amar Klar.* The paper itself is pretty straight forward, but basically he lays out a nifty basic Mendelian genetic mechanism for explaining the development of both handedness (right vs. left) and hair-whorl orientation (clockwise vs. counter-clockwise. Hair whorls and handedness have often befuddled geneticists because of some unusual traits:

  • monozygotic twins (i.e. genetically identical twins) share these traits only ~50% of the time
  • the two less common traits (cclockwise and lefties) are present across human populations at a steady ratio of ~10%
  • they also are in seeming linkage disequilibrium with each other, with lefties being ~20% cclockwise and the reverse for cclockwise being lefties.
  • Furthermore, due to its questionable genetic basis and low selective potential,** some scholars wonder whether hand-preferences are biological at all

 What Klar proposed was that handedness and hair whorls were determined by a single locus, which operates similarly to a traditional dominant-recessive Mendelian gene, with the exception that homozygous recessives have a random 50-50 chance of displaying the recessive phenotype (left-handedness or counterclockwise hair whorls). I will save you the Punnet squares (feel free to do them yourselves, though), but the math works out remarkably well. It seems like Klar’s “random gene” explanation fully accounts for both phenomenon.

What this (mildly) interesting but inconsequential paper has to do with the topic I opened the post with (the gays) is that a number of researchers (including Klar) have noted the relationship between male homosexuality and both left-handedness and counterclockwisehair whorls, with an incidence of overlap of ~20%. Similarly, if one monozygotic twin is gay, the other has a roughly 50% chance of being so as well, just as with lefties and counter-clockwisehair whorls. This all suggests that the same mechanism, if not the same gene is in play for all three phenomena, implicating Klar’s hypothetical random gene as a wider “neural orientation” gene. He has hinted at such a conclusion, implicating these three phenotypes, along with some mental instabilities, with asymmetrical brain layouts, possibly stemming a mutation on chromosome 11.

The most interesting thing, at least to me, comes from combining Klar’s randomness idea with the other thingwe know about male homosexuality, that successive male children increase the probability of the later ones being gay (hey Feynay). Its is suggested that successive male children either affect in-utero hormone production in the mother or cause a more effective immunological response on behalf of the mother against the child, affecting them such that they are more likely to be gay. All this offers Klar’s notion an epigenetic mechanism. My bet is that during development , sometime after the differentiation of the ectoderm (the layer that eventually becomes the skin and nervous system), hormonal levels/immunoresponses in-utero trigger the expression/repression of Klar’s recessive allele, assuming homozygosity, altering the protein gradient across the ectoderm (or just in splotches), causing misconfigured orientations of all sorts in the resultant baby. Testing the relationship between birth order and hair whorls/handedness would be one step towards determining the veracity of this hypothesis.

If true, though, it would offer a number of nonadaptionist explanations for the resilience of the “gay gene” despite the obvious maladaptive phenotype:

  • sheer number of carriers – this is the simplest and most effective explanation to me.  Even normal, deleterious recessives are difficult to eliminate from the gene pool, but add in another tier of carriers (the homozygous recessives who randomly do not express the phenotype) and make both sets of carriers widespread across human populations and you have an incredibly hard to kill phenotype, even if its expression is an immediate genetic dead end. 
  • pleiotrophic benefits – if Klar’s suppositions are right, then the “gay gene” is likely just one manifestation of a broader neurological gene that affects a wide range of phenotypes, likely with some beneficial outcomes.  Add in the fact that some homozygotes can express the beneficial traits without the homosexuality thanks to the randomness of the whole thing.  Though this is hardly conclusive evidence, assumptions along these lines would gel well with the observation that American presidents have a high incidence of left-handedness.
  • heterozygous benefits – similar to the the pleiotrophic hypothesis, but applying instead to those with only one of the recessive alleles.  The most common example of heterozygous benefits bolstering maladaptive traits comes from sickle cell anemia
  • , though that’s hardly the only instance. Here’s one paper summary(unrelated to the Klar hypothesis) detailing a potential heterozygote benefit from homosexuality

Of course, none of these interesting hypotheses would ever see the light of day if one’s primary motivation is less for doing science and more towards proselytizing the word of Darwin to the unsaved masses or protecting His name from theistic dissenters.
*Of note about Dr. Klar: he works for the Center for Cancer Research, and yet, as his bio attests, researches some of the least consequential and least cancer-related subjects in genetics. Next time you think of donating to some cancer fund, think of the money going straight to Klar (and then of course give plentifully). Also, do note that Klar is just one guy publishing this stuff and other scholars have disputed some of his argumentation.
**If you thought the homosexuality adaptionist stories were dubious, the lefty ones are even worse. The Wikipedia page, for example, cites the capacity for lefty swordsmen to assault medieval towers as a potential selective advantage.



  1. […] and the Gays (Again) I know I have been down this road before, but sometimes things are so egregious they must be addressed.  Andrew is in a tizzy […]

  2. […] attempt to explain homosexuality through straightforward adaptionism, this time trying to use the “male-alliance” theory to rebut the vaguely more legitimate “gay uncle” theory.  The author is right insofar […]

  3. […] and the Gays National Geographic promulgates a similar theory to the one discussed here earlier.  Similar to the Klar hypothesis, it relies on epigenetic effects during development to […]

  4. […] and the Gays More evidence in favor of my pet theory that homosexuality (and handedness and hair whorl direction) are all tied together as small, more […]

  5. […] our coverage of evo-devo and the gays, I want to highlight the recent inquiries into the use of prenatal treatment of […]

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