The Science of Gaydar looks at “New Research on Everything From Voice Pitch to Hair Whorl” and asks, “If sexual orientation is biological, are the traits that make people seem gay innate, too?”:
Statistically, for instance, gay men and lesbians have about a 50 percent greater chance of being left-handed or ambidextrous than straight men or women. The relative lengths of our fingers offer another hint: The index fingers of most straight men are shorter than their ring fingers, while for most women they are closer in length, or even reversed in ratio. But some researchers have noted that gay men are likely to have finger-length ratios more in line with those of straight women, and a study of self-described “butch” lesbians showed significantly masculinized ratios. The same goes for the way we hear, the way we process spatial reasoning, and even the ring of our voices. One study, involving tape-recordings of gay and straight men, found that 75 percent of gay men sounded gay to a general audience. It’s unclear what the listeners responded to, whether there is a recognized gay “accent” or vocal quality. And there is no hint as to whether this idiosyncrasy is owed to biology or cultural influences — only that it’s unmistakable.
Hair whorl, which may be linked to right- or left-handedness, is another predictor:
About 23 percent [of men tested at a gay-pride event] had counterclockwise hair whorls. In the general population, that figure is 8 percent.
Other indicators:
A string of other studies, most of them conducted quietly and with small budgets, has offered up a number of other biological indicators. According to this research, for instance, gay men, like straight women, have an increased density of fingerprint ridges on the thumb and the pinkie of the left hand; and overall their arms, legs, and hands are smaller relative to stature (among whites but not blacks). There are technical differences in the way most men and most women hear, except among lesbians, whose ears function more like men’s. And there are gender-based cognitive differences in which gay men appear more like women. One involves mentally rotating a 3-D object, something males tend to do better than females — except gay men score more like straight women and lesbians function more like straight men. In navigational tasks and verbal-fluency tests, gay men and lesbians tend to have sex-atypical scores.
From these findings, it might be tempting to conclude that lesbians are universally masculinized and gay men are somehow feminized — the classic “inversion model” of homosexuality advanced by Freud. But the picture is more complicated than that. There is also evidence — some more silly-sounding than serious — that homosexuals may be simultaneously more feminine and more masculine, respectively. The stereotypes — that lesbians tend to commit to relationships early and have little interest in casual sex; that gay men have more sexual partners than their counterparts — turn out to be true.
What causes gayness? It doesn’t seem genetic or environmental — at least in not in a simple way:
One of the riddles still vexing geneticists is why only 50 percent of gay identical twins share a sexual orientation with their sibling, despite being genetically identical. “We know from all sorts of research that it’s not your upbringing, not relationship with parents or siblings, not early-childhood sexual experiences and whether you go to a Catholic school or not,” says Sven Bocklandt, a geneticist at UCLA. “What I believe is that it is the ‘epigenetics environment,’ meaning the environment on top of our DNA — meaning the way that the gene is regulated. If you have identical twins, the genes are identical, but they are used differently. Every man and every woman has all the genes to make a vagina and womb and penis and testicles. In the same way, arguably, every man and woman has the genetic code for the brain networks that make you attracted to men and to women. You activate one or the other — and if you activate the wrong one, you’re gay.”
The current theory invokes the environment in the womb:
Immunological response is the ascendant theory, in fact. We know from a string of surveys that in any family, the second-born son is 33 percent more likely than the first to be gay, and the third is 33 percent more likely than the second, and so on, as though there is some sort of “maternal memory,” similar to the way antibodies are memories of an infection. Perhaps she mounts a more effective immunological response to fetal hormones with each new male fetus. To determine whether the fraternal birth order might also suggest that baby brothers are treated differently in a way that impacts their sexual expression, researchers have studied boys who weren’t raised in their biological families, or who may have been firstborn but grew up as the youngest in Brady Bunch–type homes. In every permutation, the results were the same: What mattered was only how many boys had occupied your mother’s uterus before you.
This theory may explain some things from other cultures:
Dean Hamer sees one possible answer in the fraternal-birth-order studies. “In Polynesian cultures, where you’re talking about very big families, it was typical to have the last-born son be mahu, or gay,” he says. Explorers described young boys who looked after the family and sometimes dressed as girls. “They suspected that their families had made them that way. But you just can’t take a guy and make him clean up and have him become gay. He’s got to have some gayness inside. Maybe that’s the biological purpose to the mahu: taking care of Mom.”
He says this half in jest, I think, but some other evidence bolsters his argument, including the appearance of transgender younger sons among Native Americans (the so-called two-spirits) and in premodern corners of India, Samoa, and Indonesia. A survey published this year suggested that transgender fa’afafines in Samoa are more “avuncular” than heterosexuals — that is, more likely to care for kin. Another study says that female relatives of gay men may have more children; perhaps the very thing that makes their brothers and sons gay makes them more fertile, an ideal situation with extra babysitters on hand. You can slice this stuff any way you want.
Algae may become 
I got a kick out of 
The Chinese are successfully breeding 
