Sexual-gender diversity: An evolutionary point of view

Introduction There are people with a gender incoherence between their biological gender (phenotype) and the self-perception gender. Differences among such condition and sexual orientation give us more subtypes of gender and sexual diversity: transsexual, travesties and transgender, homosexual, heterosexual, bisexual and asexual. Objective To review if there are well supported evidences about sexual and gender diversity as part of evolutionary strategies. Method Medical and political historical documents about the birth of the concepts of gender and sexual orientation were consulted at The National Library of Medicine. These were updated, in a review of the scientific literature of the last fifty years in SCOPUS, PubMed and Science Direct systems. The following words were used: homosexuality, transsexuality, gender and evolution. Results Because sexual reproduction is so indispensable and so zealously selected, the existence of homosexuality and transsexuality is a kind of paradox. One must wonder: why would not evolution quickly select against behavior, which diverts an animal from sexual reproduction? Yet despite this apparently unlikelihood homosexuality does exist. Homosexuality is also the innate sexual preference for one's own gender or the biological urge for same-sex coitus. So despite popular non-recognition of the phenomenon, natural history observations have revealed a wide range of homosexuality throughout the animal kingdom. To account for homosexuality -or any phenomenon- using evolution, it is necessary that it be natural, i.e. it must occur naturally without human influence. Thus, animal behavior is used to illustrate the naturalness of homosexuality. In essence: there are homosexual animals in nature; therefore homosexuality is natural. Transsexuality is a gender issue, and in psychiatry remains as a mental disease named "gender dysphoria". Discussion and conclusion There is some biological basis for these particular human beings, in whom the role of high levels of hormones, antibodies against testosterone receptors, order or birth is also discussed in the present article. To understand that humans are not a dichotomist species is the main goal of this work, as homo sapiens differences in many aspects of our functions are the norm.