How you just gon assume facts do
its not an assumption, it's a fact.
1. homosexuality occurs in similar proportions in animals. you're telling me mice "decide" to be gay?
2. The Royal College of Psychiatrists stated in 2007:
“ Despite almost a century of psychoanalytic and psychological speculation, there is no substantive evidence to support the suggestion that the nature of parenting or early childhood experiences play any role in the formation of a person’s fundamental heterosexual or homosexual orientation. It would appear that sexual orientation is biological in nature, determined by a complex interplay of genetic factors and the early uterine environment. Sexual orientation is therefore not a choice.
3. Professor Michael King states: "The conclusion reached by scientists who have investigated the origins and stability of sexual orientation is that it is a human characteristic that is formed early in life, and is resistant to change. Scientific evidence on the origins of homosexuality is considered relevant to theological and social debate because it undermines suggestions that sexual orientation is a choice
4. "The authors of a 2008 study stated "there is considerable evidence that human sexual orientation is genetically influenced,
so it is not known how homosexuality, which tends to lower reproductive success, is maintained in the population at a relatively high frequency". They hypothesized that "while genes predisposing to homosexuality reduce homosexuals' reproductive success, they may confer some advantage in heterosexuals who carry them". Their results suggested that "genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population". A 2009 study also suggested a significant increase in fecundity in the females related to the homosexual people from the maternal line (but not in those related from the paternal one)."
5. Garcia-Falgueras and Swaab state in the abstract of their 2010 study, "The fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb. There is no indication that social environment after birth has an effect on gender identity or sexual orientation."
evidence on evidence, all you have to do is a 5 minute read on wikipedia to get some basic facts