I
recently read Matt Ridley's The Red Queen. My answer is just a paraphrasing.
It is mostly about Genes.
In the early 1990's, there was a flurry of
interest that a gay gene had been found on the X chromosome. The
excitement faded as it proved hard to replicate the original study.
But it
was evident that homosexuality is heritable. The most compelling of
the new evidence for the gay gene is that fraternal twins, carried in the same
womb and reared in the same household, have only a one-in-four chance of being
gay. Identical twins, on the other hand, with the same nurture and the same
nature, have a one-in-two chance of being gay.
If one identical twin is gay, the chances
that his brother is also gay are 50 percent: There is also good evidence that
the gene is inherited from the mother
and not from the father.
How could such a gene survive, given that gay men generally do not have children?
There are two possible answers:
1. One is that the gene is good for female
fertility when in women, to the same extent that it is bad for male fertility
when in men.
2. The second possibility is more intriguing.The
'gay' gene might not be on the X chromosome after all. X
genes are not the only genes inherited through the female line. So are the
genes of mitochondria, and the evidence linking the gene to a region of the X
chromosome is still very shaky statistically
If the gay gene is in the mitochondria, then a
conspiracy theory springs to the devious minds of Hurst and Haig:
Perhaps
the gay gene is like those male killer genes found in many insects: It
effectively sterilizes males, causing the diversion of inherited wealth to
female relatives.
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