You're either straight, gay, or lying?

I just wanted to post here because I have been having lunch conversations with a sexologist over the last academic semester and I've learned some interesting things.First of all, it would appear to be very difficult to know what is "hardwired" with regard to sex. Remember that our main evolutionary advantage is having a big large brain which works things out, so our advantage in some sense is to not be hardwired.Secondly, the field seems to be coming down on the side of human beings being a sexually sequentially monogomous or "shamed" monogomous species. Shamed monogomous means monogomous with occasional allowance for "lapses" which are punished with "shame". Some of our ape relatives are totally monogomous, others are sequentially monogomous, some are shamed monogomous and others are not monogomous, so it can be difficult to settle this from our nearest relatives. However one must keep in mind that we didn't evolve from an animal like pack wolves, so there isn't really an evolutionary precedant for the male to deposit his sperm left, right and centre.
So scientifically monogomy probably isn't entirely cultural or even mostly cultural. The attitude to lapses could be, but that's another issue.There's some great books on this stuff ranging from academic monographs to near pop-science level. If anybody wants references just ask.

I just wanted to add something. Some of the evolutionary reasons for monogomy can be difficult to see when looking at society today. In modern times a single mother can actually raise a healthy child, but in the time of early humans this would be very unlikely considering the hardships.So a male was more likely to have differential reproductive success by "sticking around", as it would be beneficial for the health of the child.Edited by Son Goku, : Clarity.

I must admit that I am very poorly educated on homosexuality in other species. Does anybody have any ideas on why it occurs? Is it just a natural consequence of sexuality, i.e. if sex in a species is based on attraction rather than "wham, bam, thank you mam!" style sex found in insects, then that attraction can simply "wander" to the same gender, maybe?Any idea folks?

Neither, on its own it isn't a significant argument, since it can run both ways.
More accurately there are other things to consider, humans have very low sexual diffeomorphism which is correlated with monogomy in the animal kingdom. Some physical features in human males are known in other animals to be due to a monogomous set up.Let me emphasise that this is not a certain thing, it's just that the field of sexology and anthropology is currently leaning in this direction. However even if one disagrees with sequential monogomy in our species, we are not a "get with everybody" species. None of our evolutionary ancestors seemed to be set up for it.