Yes I have manny, you're just too lazy to extrapolate
there's several mechanisms, I'll go through two scenarios:
1) Homosexuality is caused by a mutation, say in the Straight gene. Fitness is caused by a mutation, say in the Lazy gene. Now, say the Straight gene is in parallel with the Lazy gene. Say within one individual (A), the Lazy gene mutates and the product is the Fitness gene. After two generations, given inbreeding, offspring of A will propagate the Fitness phenotype and be fitter than individuals displaying the Lazy phenotype. Over time, the Fitness gene will become dominant over the Lazy gene. Now, say, a direct offspring of A also has a spontaneous mutation in the Straight gene, such an individual will carry the Gay gene and Fitness gene in linkage... and hence will be carrier of Gayness. If the Gay gene remains recessive but the Fitness gene is dominant, the Gay gene will passed through the generations... when two carriers copulate, then a Mendelian proportion of the children will be homosexual.
2) Homosexuality as a byproduct from the evolution of a random silencing programme. Don't know how to begin this hypothesis. Certain genes that affect the straightness of an individual may be silenced. A randomised silencing programme is evolutionarily advantageous as it would generate variation within a population, at times, it may either accidentally or randomly silence genes that affect how straight we are. Silencing has the same affect as turning off/mutating a gene, but isn't passed down through generations.
