Homosexuality increases the number of men protecting any one family unit, without creating additional rivalry over females. A caveman family with two homosexual members will have three men protecting the offspring, thus greatly reducing the chances that the children will be eaten by animals, or killed by another tribe. As humans only have one child per year (versus, say, fish having hundreds), our survival strategy is to invest much time and resources into our few children. Homosexuality, therefore, would be evolutionarily favored, as it maintains an optimum male protectorffspring ratio in the tribe. --- Likewise, female homosexuality increases the bonding between mothers in a caveman society, keeping the group, and the children, united. Unlike males, females do not require sexual satisfaction to reproduce. Watch a season of Meerkat Manor, and you will quickly learn that female infighting can lead to tribal disaster. Homosexual or bisexual human females would preserve the integrity of stone-age tribes, ensuring their collective offspring's survival. --- Remember, any genetically-influenced traits that increase the survival rates of children will be naturally selected. Ants have literally conquered the world, and yet only a very, very small fraction of their total population can biologically reproduce. Food for thought.