Handedness and Homosexuality

In "Sniffing Out the Gay Gene" Steven Pinker suggests multiple, even concurrent, possible sources for homosexuality, instead of a binary. “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. But in this case nature probably does trump nurture. Gay men generally report that their homosexual attractions began as soon as they felt sexual stirrings before adolescence. And homosexuality is more concordant in identical than in fraternal twins, suggesting that their shared genes play a role”
I find this statement interesting in its relation to left-handedness. Both of my parents are left-handed, and I am right-handed, which is reasonably probable, but surprising. My birthmother assumed I was also left-handed, and my left-handed partner assumed one of my parents was lying until we investigated the statistics. The fact that amuses me is that a left-handed twin has a 76% chance (according to the Wikipedia summary, which references a neurology article) of a right-handed twin. So, genetics are not the only factor in determining handedness. In fact, my birthmother assumed that I would be left-handed, but she herself later switched to right-handedness to
Socially, we generally assume handedness is precisely defined by genetics and recall sympathetic references, and even stories from our older relatives and friends, about having the "sinister" side beaten out of them, forced to live constantly mildly uncomfortable, or at least illegible, lives as a binary they are not. Yet, while handedness is clearly largely decided prior to learning to write, it is not entirely decided genetically or even prenatally due to the significant difference between those with the same DNA.
"Most likely, the environment plays a role. There are probably one or more genes that make you more likely to become left-handed. You then need some sort of environmental trigger for it to happen," claims Dr. Barry Starr of Stanford University, in Understanding Genetics. He goes on to explain that birth order, specifically prenatal hormones, significantly effect left-handedness in chimpanzees, in which it is much more common than humans. It has so far been seen, according to Starr, that pregnancies in older human females result in more left-handed children. Of course, this slightly contradicts the ability of those who share a womb and genetics to result in differing handedness, but it further examines the variety of biology, which is frequently considered binary, fatalistic and final.
I would not go so far as to suggest that any of the specific determining factors of handedness directly relate to sexual orientation. I simply feel that the comparison, as a way of studying genetics, is a good analogy with which to consider Pinker's analysis. Amusingly, I am a bisexual person who spent a semester with a broken dominant hand, I learned comfortably to use my left. A gay classmate earlier broke his dominant hand and cried daily attempting to complete assignments. Perhaps I am more naturally adaptable to my environment than others. Perhaps it's coincidental. In general, however, I support Pinker postulating that homosexuality is simply more complex than one single determining factor, be it nurture or nature. I celebrate the diversity of possibility, in the same way I celebrate the diversity of sexuality.

Starr, Barry. "Ask a Geneticist." Understanding Genetics. 2004. The Tech Museum of Innocation. 1 March 2009 .