The New York Magazine has an in-depth article on the science of sexual orientation and whether the biological factors which may make someone more likely to be gay, also make them more likely to appear gay to others.
There are now a range of established findings that suggest that gay men are likely to have a number of physical traits not shared by straight men (the findings on gay women are a lot less clear-cut it seems).
For example, a 2004 study [pdf] found that gay men were much more likely to have a counter-clockwise hair whorl (as pictured) than straight men.
Other studies have found differences in finger lengths, size of structures in the hypothalamus (a deep brain area), and on a number of psychological abilities like mental shape rotation and navigation to name but a few.
Some researchers believe that the same biological conditions that increase the chances of homosexuality, also increase the chances of some of these body, brain and mind differences.
While genetics is thought to play a part, researchers are also interested in the time when an unborn child is developing in the womb.
Interestingly, many of the differences are linked to hormone exposure in the womb and can be seen to different degrees in both gay and straight men.
One of the critical questions is still how much of the influence is to do with biological factors and how much with social influence, opportunity and freedom of expression.
The New York Magazine is a fantastic guide to the science of sexual orientation, but is also a wonderful commentary on how this research is perceived by parts of the gay community and what it might mean for gay politics.
The only slight drawback is that it repeats the ‘scientists tried to turn sheep gay’ myth, but apart from that, it’s a compelling read.
UPDATE: Discover Magazine just had a feature article on the genetics of homosexuality which accompanies this piece nicely.
Link to article ‘The Science of Gaydar’.