All people are simply "sexual" beings and heterosexual vs. homosexual lies on a continuum. We have an unusually high sex drive because females hide mensus.
ie. Many\most people will participate in homosexual sex under extreme social pressure (prison).
Most of the time there is a defined and distinct preference, but experimentation is not necessarily unusual.
Bonobo Monkeys are evidence of this.......
The scientific name for the Bonobo is Pan paniscus. As their DNA is more than 98% identical to that of Homo sapiens <3>, they are more closely related to humans than to gorillas. Another study on the similarity of critical DNA sites in human and Pan genes suggests that 99.4 percent are identical.
Bonobo males frequently engage in various forms of male-male genital sex (frot).<12> <3><4> One form has two males hang from a tree limb face-to-face while "penis fencing". Frot may also occur where two males rub their penises together while in missionary position. A special form of frot called "rump rubbing" occurs to express reconciliation between two males after a conflict, where they stand back-to-back and rub their scrotal sacks together.
Bonobo females also engage in female-female genital sex (tribadism) to socially bond with each other, thus forming a female nucleus of Bonobo society. The bonding between females allows them to dominate Bonobo society - although male Bonobos are individually stronger, they cannot stand alone against a united group of females. Adolescent females often leave their troop of birth to join another troop. Sexual bonding with other females establishes the new females as members of the group. This troop migration mixes the Bonobo gene pools.
http://en.wikipedia.org/wiki/BonoboI would argue that morality evolved with religion. It has been used to keep people in line. Keeping people in line usually involves oppression as you have the simultaneous process of elevating some groups above others.
Remember that story that ended with the guy who felt better about himself when he met someone with no feet?