Mating types in yeast, vomeronasal organ in rodents, homosexuality in humans: does a guiding thread exist?

Pheromones and their receptors are the molecules used by very different organisms in order to join two haploid cells. It happens evidently in yeast, since the two blending haploid cells are also the two mating organisms, whereas in rodents pheromone receptors are the triggers of the vomeronasal system which, supervising sexual behaviors, is responsible for copulation and therefore for fertilization. The debate is still open about the real significance of pheromones in humans but a working vomeronasal organ, able to recognize pheromones of the same sex, could be the simplest biological explanation of homosexuality. This hypothesis is discussed and connected with some well known experimental data.