http://www.nytimes.com/2003/10/25/opinion/25KRIS.htmlGay at Birth?
By NICHOLAS D. KRISTOF
Earlier this year, the journal Personality and Individual Differences published an exhaustive review of the literature entitled "Born Gay?" After reviewing the twin studies, it concluded that 50 to 60 percent of sexual orientation might be genetic.
Many studies also suggest that sexual orientation may be linked to differences in brain anatomy. Compared with straight men, gay men appear to have a larger suprachiasmatic nucleus, a part of the brain that affects behavior, and some studies show most gay men have a larger isthmus of the corpus callosum — which may also be true of left-handed people. And that's intriguing because gays are 39 percent more likely to be left-handed than straight people.
Now look at your fingers. Men typically have a ring finger that is longer than the index finger, while in women the two are about the same length. However, two studies have suggested that lesbians have finger-length ratios that are more like those of men than of women.
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