This month has been Queer Awareness Month at many universities across Britain, with four weeks of stalls, debates and films to promote queer human rights.

Given that homophobia still exists, we need to challenge prejudice and defend our right to be gay. But in the long term, lesbian and gay identity is doomed. And a good thing, too.

Like every other expression of human culture, homosexual and heterosexual identities are historically transient. They haven't always existed, and they won't last forever. Indeed, the weakening, blurring and eventual dissolution of the labels queer and straight will be final proof of the demise of homophobia.

When I made this point in a recent university debate, I was greeted by howls of protest from some lesbians and gays in the audience:

"Mr Tatchell, you are obviously suffering from internalised homophobia," said one. Another interjected: "You are playing into the hands of homophobes."

Well, no. I was trying to express a truth that some gay people find disconcerting: while same-sex behaviour has existed since the beginning of human evolution, defining oneself as gay is a relatively modern invention and is unlikely to prevail in perpetuity.

Homosexuality and homophobia exist in a cultural context, as do heterosexuality and heterophobia. Culture is man-made, not biologically given. It evolves and changes.

Historical and anthropological research shows that same-sex behaviour has occurred in all cultures at all times - but in different manifestations. Homosexuality in pre-colonial African and Asian societies was very different from its counterparts in Ancient Greece, Confucian China, Tudor England and 21st-century western Europe.

Clellan Ford and Frank Beach's classic anthropological survey, Patterns of Sexual Behaviour (1952), documented the huge diversity of same-sex relations in dozens of tribal societies on every continent. They debunked, once and for all, the myths that homosexuality was a European phenomenon and a state of desire that was universally the same.

They also demonstrated that most non-western cultures seem to have accepted, and sometimes even venerated and ritualised, same-sexers. In many native American tribes, for example, this sexual difference was deemed to be evocative of spiritual and supernatural powers. The prestigious role of tribal shaman was often reserved for these "sexual others".

Modern western expressions of gay identity, behaviour and subculture only began emerging a mere three centuries ago in the European cities of Amsterdam, London, Florence and Paris.

Up until this time, there was only same-sex behaviour, not same-sex people. Contemporary gay identity - the definition of oneself as gay - did not previously exist. According to the medieval Church, the "abominable vice" of sodomy was not the sin of a specific class of people, but an "evil temptation" to which anyone could succumb.

Prior to the 1700s, there were no gay social milieux. Then came the bawdy private parties held in the "molly houses" of 18th-century London. These were forerunners of modern gay bars. Long before Hampstead Heath, there was a gay cruising ground in the gardens adjacent to Buckingham Palace. This is how the "gay scene", as we now call it, began.

History shows us that same-sexuality was, and is, an evolving cultural phenomenon. The idea that queers are a distinct class of people and are fundamentally different from straights is historically very recent, originating primarily from the normative theories of late 19th-century psychology. Indeed, the word "homosexual" was only coined in the 1860s. Before then, no such term existed.

This would seem to suggest that just as the contemporary configurations of gay identity came into being at a certain moment in social development, one day, if social conditions change, they will also fade away. So will heterosexual identity, as we currently understand it.

The labels gay and straight are cultural inventions, primarily devised to police sexual desire. By labelling same-sexers as a distinct group of people, society marks them out as "different" and "other". This has functioned as a way to identify, marginalise and control the queer "menace".

In a future, more enlightened epoch, homophobia will be vanquished. Anti-gay attitudes will be deemed as ridiculous as flat-earth theories and opposition to votes for women. In this non-homophobic society, the present separate, exclusive sexualities of straight and queer are likely to be eventually supplanted by a more inclusive, polymorphous sexuality. This dissolution of rigid hetero and homo orientations and identities is thus both the precondition for, and the proof of, queer emancipation - for without differentiation and polarity, there can be no conflict and prejudice.

The boundaries between hetero and homo will merge and blur, with a greater incidence of bisexuality. Most people will stop defining themselves as straight or gay, and the gender of a person's sexual partner will cease to determine the social validity (or illegitimacy) of their carnal and affectional feelings. People will be accepted, whoever they love.