Human Sexuality: Choice or Chance?

Hmmmm....this topic is one that has sparked-off widespread arguments and discussions from time immemorial.
Human Sexuality refers to the status of being homosexual (gay), heterosexual (straight) or bi-sexual. Homosexuals are men who love other men as well as women who love other women; Bi-sexuals love both men and women and a lot of people tagged as gay and lesbian are usually bi-sexual. There is also Transsexualism, which implies a condition in which an individual identifies with a gender not culturally-associated with their assigned sex. Simply put, it describes a situation whereby an individual does not like his or her natural gender and wishes to change to the opposite gender. That is, a man choosing to become a woman and vice versa. This is possible through a medical procedure called Sex Reassignment Surgery and is currently well-known in the Western world.
The practice of  homosexuality dates back to the ancient times.
From the Biblical account of the events in Sodom and Gomorrah to ancient African, Asian and European times. In Africa, before the 20th century, women in Lesotho were involved in social-sanctioned, long-term erotic relationships called 'Motsoalle'. Also, male Azande warriors in Northern Congo routinely took on young male lovers between the ages of twelve and twenty, who helped with household tasks and participated in non-penetrative intercourse with their older husbands. Also, the first recorded homosexual couple in history were Egyptians, commonly known as Khnumhotep and Niankhkhnum, who lived around the 2400 BCE (Wikipedia).
From the Biblical point of view, Homosexuality in all its forms is prohibited in the Book of Leviticus and that has been the main focus of people who are homo-phobic. Homosexuality in Christendom is generally linked with demon-possession and persons involved are often requested to repent and be delivered. Science on the other hand, has not arrived at any clear-cut reason behind people's sexual orientation. There has been an on-going debate referred t as the Nature-nurture controversy, meaning that some scientists believe that homosexuals were born that way while others believe that the environment and circumstances made them so. However, scientific evidence shows that most homosexuals were raised by heterosexual parents while most children raised by homosexuals grow up to become heterosexual.
In Nigeria, the homosexual population is growing daily and the practice is becoming widespread. Nowadays, we have both single and married men and women indulging in the act; some women have attributed it to heartbreaks caused by their heterosexual spouses, some have attributed it to peer pressure, some think it is just about being adventurous and trying out new options, some people have blamed the western media and culture for its infiltration into our country, while some people cannot explain the reason for their choice. There are people who have never had heartbreaks from heterosexual partners, as a matter of fact, some people are happily married, yet find themselves intertwined in that web. Some people have said that women who engage in lesbianism do so because they are unable to attract men; I particularly disagree with this because I am aware that a good number of lesbians are very beautiful and would attract virtually any man that beholds them. Thus, the question pops: why exactly are people gay or straight? Is there a 'cure' to it? Feel free to air your views and share your knowledge.