If the gene were recessive, requiring two copies for expression, then it could persist in the population. If it also had another beneficial result then it would be even more likely to persist. I am not saying I agree that homosexuality is genetic (I think it’s far more complex than that) however just because a gene keeps one from being reproductive in some instances, does not mean it will die out.
http://www.mygenes.co.nz/summary.pdf
Those researchers who know most about genes and SSA say “Your genes did not make you do it”.
Let’s review the evidence bearing in mind that many of the following arguments apply to all human
behaviours.
Genetics:
Science has not yet discovered any genetically dictated behavior in humans. So far, genetically
dictated behaviors of the “one-gene-one-trait” variety have been found only in very simple
organisms. (Ch 1)
From an understanding of gene structure and function
there are no plausible means by which
genes could inescapably force SSA or other behaviors on a person (Ch 1)
No genetically determined human behavior has yet been found. The most closely geneticallyrelated
behavior yet discovered (mono-amine oxidase deficiency leading to aggression) has
shown itself remarkably responsive
to counselling. (Ch 1)
If (exclusive) SSA were genetically inherited, it would have bred itself out of the population in
only several generations, and wouldn’t be around today. (ie. gays with no children would not be
able to reproduce their genes.) (Ch 1)
Generally, geneticists settle for some genetic influence
of rather undefined degree, most
agreeing that many genes (from at least five or six to many hundreds) contribute to any
particular human behavior. (Ch 1) This means:
If SSA were caused by many genes it could not suddenly appear and disappear
in families the way it does. It would stay around for many (eg. at least 30)
generations because it would take that long for that many genes to be bred out.
Therefore SSA cannot be caused by many genes. (Ch 1)
The occurrence of SSA (2.6%) in the population is too frequent to be caused by a chance
mutation in a single gene. Therefore SSA cannot be caused by a single gene. (Ch 1)
Researchers trying to find “homosexual” sequences of genes on the recently mapped
human genome have not found any such sequences although they have found them for
schizophrenia, alcoholism etc. (Ch 9)
The occurrence of SSA is about five time too high to be caused by a faulty (non-genetic)
pre-natal developmental process, so it is not innate in that sense either. (Ch 1)
First same-sex attraction occurs over a very long time span, unlike pre-programmed genetic
events eg puberty, menopause. This argues that first same-sex attraction is not a genetically
programmed event. (Ch 1)
The human race shares most of its genes - something between 99.7 percent and 99.9 percent.
That means all ethnic groups will have most of them. This has the following three implications.
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If homosexuality is genetically dictated, homosexual practices will be identical or
extremely similar in all cultures. But there is an enormous range and diversity of
homosexual practice and customs among different cultures (and within cultures)
(Ch 6)
There would be a similar incidence of homosexuality in all cultures. But
homosexuality has been unknown in some cultures and mandatory in others.
(Ch 6)
Changes in homosexual practice and behavior in different cultures would take
place very slowly, over many centuries. But this is not what history shows. The
decline of whole models of homosexuality (the Greek, over a couple of centuries,
and the Melanesian, within a century); the relatively sudden [in genetic terms]
emergence of the present Western model over a couple of centuries; and abrupt
changes of practice within an ethnic group, even over a single generation, are not
consistent with anything genetic. Even less so the swiftly changing sexual practices
within the current Western model. (Ch 6)
The drop in SSA attraction and practice over the lifespan is too great to attribute to genetic
change – or for that matter, deaths from AIDS. It could indicate some change in sexual
orientation. (Ch 2)
Recent increases in the percentage of those experimenting with same-sex behaviour suggest
social influence rather than genetic change. (Ch 2)
Dean Hamer, one of the strongest advocates of a genetically-based homosexuality, has
remarked that he doesn’t think a gene exists for sexual orientation. (Ch 9)