And now the Anthropological point of view....

Like bard has alluded to earlier- there is a difference between preference and behavior. Psychologists say that sexuality lies on a continuum. This certainly seems to be true.

We are also all a product of nature and nurture. Homosexuality does exist within the animal kingdom. And there does seem to be some evidence for a genetic predisposition. Take for instance individuals with adrenogenital syndrome- I think is the one- where a person is genetically male but looks like a female and has functional female anatomy but cannot reproduce. These people will be lesbians most of the time, but not all of the time. There are also studies that seem to indicate that the structure of male homosexual brains are somewhat similar to the brains of heterosexual females. Some scholars point to chemical imbalances or prenatal stress or defects in development from a "female" embryo to a "male" one to explain homosexuality.

It seems if homosexuality is genetic then it would be polygenic and not the cause of one individual trait.

But it seems like homosexuality is also a cultural- perhaps an evolutionary cultural- adaptation.

Not all cultures even have a concept for "homosexual" or "gay"- Yet homosexual behavior's are socially encouraged or sanctioned in some socieities.

In the African tribe of the Sambians- sodomy (anal sex) was encouraged among the male warriors. They called this "boy-insiminating" rituals. Older males would have sex with the young males in order to make them more masculine. The sex was also designed in order to strengthen the bonds between the males. You are more likely to fight for and protect your lover than an acquaintance or even a friend. Men could take "boy wives" until they come to accept a female wife. Once the men are married to women they no longer engage in homosexual acts.

In another tribal group- I can't remember its name but its in my Anthro book- the men believe that they only have a limited amount of semen. To replinish their semen in order to reproduce with the women- they believed that they had to have oral sex with other men and ingest thier semen. Again here is where homosexual behavior is social duty.

However there are also tribal groups who believe that sex is only for reproduction and discourage and punish anyone who is found to be having sex for pleasure or too much sex. Some believe that these acts hurt the social group or could bring about bad spirits or punishment from the gods. In some groups married men and women sleep apart most of the time until they plan to reproduce. So No it is not only religions like Judiasm, Christianity, and Islam or modern society that teach that sex is only for reproduction between man and woman.

And there are also tribal groups that believe that sex is a pleasureful act and include sex and orgies into religious rituals, ceremonies, and even creation myths.

Of course there are also societies that practice polygeny (multiple wives-usually sisters), polyandry (multiple husbands-usually brothers), arranged marriages etc. And there are human and animal groups that practice monogamy, polygamy, or serial monogamy. Some animals mate for life and other's don't. There is some evidence suggesting that whether you desire to be monogamous or polygamous may be due to genetic predispositions in studies done with humans and in other primates

Many Native American groups such as the Navajo and some of the Pueblo's include the creation of the feminine male and the masculine female in their creation stories. These people are called Two Spirit people because they have attributes of both males and females and can do male and female work.

Sometimes these people included what we call gays and lesbians but it also included transexuals and transvestites etc.
Sometimes same sex marriages were allowed between a Two Spirit and a individual of the same gender. Often same sex marriages were a part of Native American religious ceremonies. However if these marriages fell a part- the Two Spirit individual almost always re-married someone of the opposite sex.

These Navajo and Pueblo creation myths also include the creation of hermaphrodites- individuals with both male and female genitals.

Of course we also had the Ancient Greeks- who at first thought that true love was only between men and it was prestigious for a married man to have a male "mistress". This was to help the younger men to be able to have more social mobility. He became something of an apprentice and was able to enjoy the social life of his older male lover. Also it is said that while they would engage in sexual acts- the young boy was never to be penetrated by the older man. It seems as though sodomy was not a part of this custom.

Also in West Africa- women were allowed to marry other women. They could take on a wife and assume the position of female husband. She would have to take care of her wife and when her wife had children with men- they would become her children. In most cases these were business and social deals and Not lesbian relationships.

However there are evidence that lesbian relationships were/are prevalent in harems and as well in female military groups like the Dahomey. Not quite the Amazons- but there was a "king" who kept a private female military that protected him.

Also we know that conditional homosexuality exists in prisons and sometimes in the military. A heterosexual male may engage in homosexual acts if he is isolated from women.

Anyways it is obvious that sex if primarily for reproduction. Successful Evolution depends upon sexual reproduction for the variance of genes and natural selection. Also mutations really are the key to evolution, literally. And sexual reproduction is very important at creating new mutations.

However sex also has a secondary cultural and social function. To create bonds between individuals and in the forming of alturistic family groups. Romantic love is a social construction and is not found in all societies and cultural groups. Love is but romantic love is not. This doesn't have to do with this discussion- just wanted to point it out. Incest also seems to be a universal taboo in all culture groups. True incest was sanctioned in several royal lines (European, Eyptian etc) but this was due to religious beliefs and incest was still taboo among the common people and everyone else. It still happened but the cultural norm frowned upon the activity.

Some animals like the Bonobo Chimpanzee use sex as a way to diffuse hostile situations. When an individual gets angry- they will start to initiate sex acts to calm down the group. Sex acts such as mutual masterbation and touching and supposedly oral sex have been observed to take place between male and female chimpanzees as well as two males or two females.

Homosexuality in respect to preference does seem to stem from a polygenic genetic predisposition but is expressed through cultural and social constructions and adaptations. It occurs in humans and animals but in a much lower percentage than do heterosexuals.

Homosexual behavior seems to be more of a cultural evolutionary adaptation- a way of forming strong bonds between members of the same gender and also to help raise children in their families. This seems to be a function in several human and animal groups.

Some think that it could be a way to limit the population but I don't think there are credible evidence for that. I'm not sure though. Some think it is an evolutionary adaptation selected for because of its cultural advantages while other's think that it throws a monkey wrench in the concept of Evolution- where sex is for reproductive success.

Today with human rights movements, social acceptance, and the acknowledgment that gay relationships can be loving and stable- homosexuality preference is becoming a valid life style and seen as an orientation.