Tuesday, May 17, 2005

More on genetics and homosexuality

A nice piece by Steven Pinker taking off on the pheromone study that I discussed a couple posts ago. He also makes the point that I was trying to make here: "The difference in the brain responses of gay and straight men does not, by itself, prove that homosexuality is innate; after all, learned inclinations, like innate ones, must reside somewhere in the brain."

I'm less sure about his take on the origins of homophobia, but this line is funny enough to quote:
Why didn't evolution shape straight men to react to their gay fellows by thinking: "Great! More women for me!"

10 Comments:

Anonymous Anonymous said...

This is one of those areas where Pinker strikes me as just plain stupid. It's not because he's wrong here, but because he makes the same argument that those who believe brain differences = genetic differences make, but in other realms. The best example was his recent defense of Summers, but his writings on evolutionary psychology are full of such assertions.

In defending Summers, he argued from behavioral data (there is some neuroscientific data as well, but I don't know that Pinker has ever mentioned it) showing that there are differences in mathematical/spatial reasoning abilities between males and females, and he assumes that these differences are innate. The truly frustrating part is that, while there is absolutely no evidence that the math/spatial reasoning abilities are innate, there is evidence for the heritability of homosexuality (in the form of twin and family studies). So, while Pinker is quick to note that neurological differences are not evidence of innatenes for a trait that, in all likelihood does have a genetic component (based on the actual evidence), he's just as quick to infer that another trait, for which there is no real evidence of any innate component, is  innate based on behavioral/neurological differences. 

Posted by Chris

5/17/2005 05:06:00 PM  
Anonymous Anonymous said...

Ooh... I didn't think of that connection! Thanks for pointing it out, Chris. 

Posted by Andrew

5/17/2005 08:33:00 PM  
Anonymous Anonymous said...

Ooh...

Eww...

I think good ole Chris is full of well-intentioned crap on this sexual subject. But then I also know better than to point out why without invitation.

So I won't.

:D 
 

Posted by dan

5/18/2005 12:12:00 PM  
Anonymous Anonymous said...

"I think good ole Chris is full of well-intentioned crap on this sexual subject. But then I also know better than to point out why without invitation."

This has to rank right up there with "Ooh I have some mind-blowing gossip! Oh, but it's a secret, I can't tell you" and "Oh my God this dish is disgusting! Here, try some" as a statement that seems very weirdly disingenuous...

But please, do go on.

I'm not sure I'm the right person to debate about the actual merits of the claim that men and women have innate differences in ability at math and science, as my knowledge of the state-of-the-art in that research area is pretty limited. But Chris  seems to be quite a knowledgeable cognitive scientist, so I think if he is checking this comment thread he might be able to respond to your gauntlet throw.

Chris has some more substantive posts on the Summers fiasco here, here, and here

Posted by Andrew

5/18/2005 11:49:00 PM  
Anonymous Anonymous said...

There is a huge literature on the genetic and other biological factors in sexual orientation. There have been several twin and adoption studies over the last couple decades.

For a couple reviews of the twin-study/genetic analysis literature on homosexuality, check out these papers (the second is critical of the extant studies, but provides a nice overview):
Pillard, R.C., & Bailey, J.M. (1998). Human sexual orientation has a heritable component. Human Biology , 70(2), 347-365.
McGuire, T.R. (1995). Is homosexuality genetic? A critical review and some suggestions. Journal of Homosexuality, 28(1-2), 115-145.

The gist of the story seems to be that there are heritable components to sexual orientation (Pillard and Bailey come up with a heritability of .5, which means that about 50% of the variance in sexual orientation is due to genetic variance). It may be stronger for female homosexuality than for male homosexuality, but that finding hasn't been replicated to my knowledge. There may also be some mediating factors that are highly heritable, such as gender conformity, as indicated by some recent twin studies (e.g., one using a large Australian sample by Bailey, Dunne, and Martin in the late 90s).

There are also some biological factors that are probably present from birth, but which may not be due to genetic factors (or at least not a result of the individual's genes, but the mother's instead). The most well-researched non-genetic biological factor is the prenatal level of testosterone. There are all sorts of indirect indications (e.g., larger genital size, higher adult testosterone levels, and smaller 2nd to 4th digit length ratios) of higher levels of prenatal testosterone in homosexual men. Of course, this doesn't say much about the causes of homosexuality in women.

By the way, if Dan wanted to know my sexual orientation, all he had to do was ask! 

Posted by Chris

5/19/2005 08:06:00 PM  
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