Comment #214937 by irate_atheist

Where the relationship(s) are exclusively homosexual, and given that homosexuality is - at least primarily - genetically determined, surely exclusive homosexuality cannot be selected for? I may be wrong - I probably am - but you seem to be suggesting a kind of group selection

Gosh no. I would never do that!

Here is a suggested selfish gene mechanism. It's probably completely wrong, but illustrates that such a mechanism is possible.

There could be some genes in the mother that, given certain environmental conditions (such as having many children, or being at a certain population density), changes the hormonal environment in the womb during pregnancy to produce an increased tendency for homosexuality. These children would not reproduce, but assist with the raising of previous children, or the mother's current or future grandchildren. These children would also assist with mixing of genes by encouraging links with other families through same-sex relationships.

Such genes would be entirely "selfish". They would assist their own reproduction by the production of "helper" offspring who would help increase the frequency of these genes.