Tuesday, June 17, 2008

Gay brains structured like those of the opposite sex

MRI scans of 25+20+25+20 = 90 people have supported a proposition that many people have "known" for quite some time: homosexual men's brains are structured like the (straight) female ones and lesbians' brains are structured like the (straight) male ones.
ABC, BBC, Reuters, Sci. American, 100+ others
Homosexuality is therefore determined before the birth. It is the first time when MRI scans were used to look at this question.

The researchers from the Karolinska Institute, Sweden - where the medicine Nobel prizes are decided every year - have shown that the straight male and lesbian brains are larger and left-right asymmetric. The straight female and gay male brains are smaller and symmetric.

The amygdala seems to be the region of the brain - responsible for emotional reactions (both CPU and RAM) - that shows the identity most efficiently. It is enough to look whether the nerve connections are mostly in the left half or the right half: you find out that the straight men and lesbians have connections mostly on the right side of the amygdala and vice versa.


  1. Lubos,
    This is far from a proof of causality. Could it be that homosexuals identify (by nature of their preference) with straight members of the opposite sex and so develop and nurture similar parts of the brain in an effort to emulate them?

  2. There has been a lot of studies done on this topic, but the most interesting (and, in my estimation, conclusive) have been reviewed in Scientific American back in the late 1980s...at least, concernig the male brain.

    It had been noticed that men born durnig WWII were more likely to be gay than men born during the post-war period.

    The culprit identified then was testosterone - and its release in the male fetus. Or rather, the absence of (or deficiency in) its release during a specific time of fetal development.

    It has been demonstrated that stress causes pregnant women to release a hormone which interferes with the proper release of fetal testosterone. There is about a 3 week window, at the cusp of the 1st nad 2nd trimester, when the male fetal brain alters its development based on the presence (and level) of testosterone (released by the testes of the fetus).

    It actually affects 3 very discrete areas of behaviour: one relates to partner-preference (male vs female), another refers to self-perception (feeling like a female trapped in a male body), and the third controls affect (men looking and behaving in effeminate manner). The timing of the testosterone release dictates which of these discrete areas will fail to be affected and remain in the 'feminine' mode.

    That is why some effeminate men are straight and some gay men are not effeminate at all.

    Last year, Scientific American wrote about a follow-up study that built on these previous findings. It found that pregnancies with male children cause the mother's body to build up certain hormones that protect her against fetal testosterone. This effect is cumulative, resulting in a increase in probability of effeminate/gay/trans-gender boy being born in direct proportion to the number of older brothers he has.

  3. xanthippaschamberpot,
    Interesting idea. But isn't virilization a two stage process, occurring during fetal development as well as during puberty? If I'm not mistaken (I'm not a biologist or Dr.) testosterone also grows the male brain during puberty.

    Finally, I'm still skeptical, because even if a male has an effeminate mind this does not imply to me that he will be attracted to other men (except in the way that one is drawn to someone who is different). Here is a sketch of proof: A moments reflection reveals that it is impossible for the mind to create a template of an ideal mate prenatally. We do not have some silhouette of the perfect woman that we can match against the image of real women. Instead we build these ideas throughout life, and the best hint that our biology can give us is
    a)we can be intrigued by the differences between sexes. and,
    b)chemical receptors in the nose, which upon detecting certain pheromones can fire a biological response.
    I believe b) has a weak effect and a) is only good for generating interest, not relationships. Could you provide links to these articles?