On Wed, 1 Dec 1999, Rob Harris wrote:
> Nice one! I'd never thought of that possibility. Of course, the first thing
> that came to me was "How can Homos pass on their genes for any amplification
> of effect to be made? But then I thought "Perhaps the presence of the
> recessive gene in the pool as a whole is preferable, and so is indirectly
> propagated by the reproducing carriers"....
This is a heterozygosity effect (with perhaps moderation or promotion by other genes). The best example is sickle cell anemia. Homozygous for non-sickle cell gives you malaria, Homozygous for sickle cell gives you a bad case of the disease (with malaria resistance), but hetrozygous gives you some resistance to malaria without giving you the disease.
Other traits that I'm fairly sure have this type of characteristic include storing/burning execess energy supplies and conservative vs. adventursome personality traits (i.e. do you "stay" or "go" in the face of an erupting volcano).
In these cases, a minority in a population will carry the trait, in times of "stress" the fraction of the population with that trait will increase (because they survive the hardships), but when the environment returns to normal it will decrease to a lower level because it confers a survival disadvantage in those times.
I think homosexuality might to some degree simply a strong dose of human "hypersexuality" combined with a loss of discrimination for the a biologically "productive" mate (or a mixup in the "type" of mate one is attracted to). Humans have been selected for hypersexuality, but I suspect there are pressures against that since if you are really indiscriminant, you leave yourself open to attack by individuals with whose partners you have enjoyed yourself.