# Re: Model of how a gay gene could be propogated from generation to

Thu, 2 Dec 1999 03:52:50 EST

In a message dated 12/1/99 11:41:20 PM Pacific Standard Time, hal@finney.org writes:

> Harvey Newstrom, <newstrom@newstaffinc.com>, writes:
> > 2. Imagine a reproducing couple, each of whom has one gay gene. They
are
> > both therefore straight.
> >
> > 3. They mate and randomly pass on one gene each: Gg x Gg =
> >
> > One fourth of their children will be gay (GG) and will carry the gene.
> > One fourth of their children will be straight (Gg) and will carry the
> > gene.
> > One fourth of their children will be straight (gG) and will carry the
> > gene.
> > One fourth of their children will be straight (gg) and will not carry
> > the gene.
>
> So we went from 100% carrying the gay gene to 75% in the next generation.
> Or if you count percentage of breeders, it is 67%. This will continue
> to drop each generation, eventually eliminating the gene from the pool.
>
The math of these kinds of things has been worked out (Futuyma, Evolution Biology, 2nd edition, p, 160). The equilibrium frequency of carrier expressing these deleterious (to the gene) recessive mutant is:

(rate of mutation to the allele)/(1 -selective disadvantage)

the rate of mutation is at most 1 in 100,000. Selective disadvantage for a gay gene affecting only one sex, reducing the expected number of children by 20% in the affected sex is 10%. So with those very favorable numbers, 1 in 10,000 would be gay. *Way* too few.

So there must be some kind of advantage for genes predisposing people to homosexuality. I speculated some time ago that a sexual interest in one's own sex would help one notice and copy attractive fashions and behaviors. In that case individuals carrying a small dose of the "gay genes" might be at a net advantage and that could easily make up for the reproductive disadvantage of practicing homosexuals. You could certainly think of other benefits to "gay genes", manipulation of sex hormones, and different possibilities are not mutually exclusive.