It's hardly "any and all". In fact you'd be much harder pressed to find a scientific study that claimed homosexuality wasn't at least predisposed in part by genetics. Not to say that they don't exist -- just that they're not nearly as prevalent. You can't get 2 doctors or scientists to agree exactly what causes heart attacks, let alone what causes homosexuality.
But most scientific studies conducted on homosexuality has proved it to be, at least in significant part, a genetic anamoly. Numerous studies have reached the same conclusions -- that the X chromosome contains the genes that are the largest 'causes' of homosexuality. It is unlikley that there's a single gene though and finding the exact combinations of genes that 'cause' homosexuality will take time. Genetics still is far from an exact science, but every year scientists get closer to pinpointing the genes that cause homosexuality.
