The question of the causes of homosexuality has been present in different discourses and scientific and philosophical investigations throughout the modern era. Heirs to the more traditional and conservative conceptions of the Middle Ages that marked the beginnings of modern science, the questions about sexual “minorities” have been addressed and reformulated in an important way from different perspectives.

In this article we will briefly review some of the main scientific theories that have been asked about the causes of homosexuality . We also reflect on the implications of constantly asking ourselves about the causes of what is represented as “the different”.

What are we wondering about?

In 1973, the American Psychological Association published the second version of the diagnostic and statistical manuals of mental illnesses, with the intention of unifying the clinical views on what is considered a disorder. This version includes an important change with respect to the previous one: homosexuality was removed from the compendium of disorders , with which it was no longer considered a mental pathology.

This was only a first step, partly as a result of the social mobilisations of homosexuals themselves. For its part, the world health organization removed homosexuality from its International Classification of Diseases until the 1990s. And it was not until the first decade of the year 2000 that the APA issued an official statement in which it affirmed that there was no scientific validity in the “corrective therapies” of homosexuality that continued to be implemented in different places.

None of these measures seem to have resolved the doubt of many scientists and non-scientists as to why there are non-heterosexual people (and therefore, have not entirely ended the social need to “correct” or expel them).

The question of “what is different”

As it happens with other “minority groups” (in which the difference before the hegemonic groups is highlighted in an important way), the question about what is the origin of this difference does not stop being asked from different investigations; which, paradoxically, are constructed and presented as neutral.

This is partly a consequence of the fact that minority groups are often stereotyped from the prejudice of danger, the malicious, the less human or even the inferior. Thus, it is also frequent that, when they are not made invisible, they are represented from the place of antagonism.

This means that, a priori, many of the research questions have taken as their starting point and reference the heterosexual subject (man) and, from his body, experiences, desires, etc.; the questions about everything else have been formulated and answered.

This being the case, it is not surprising that even in professional training courses in psychology and related areas the question of the causes of homosexuality is still being asked. In other words, at the root of many research questions is an often invisible homophobic ideology. To exemplify this, we could do the brief exercise of asking ourselves why no one, or almost no one, is wondering (neither in research nor in everyday life), about the causes of heterosexuality.

Theories on the causes of homosexuality

Thus, a series of researches, with different scientific perspectives, have been developed to explain homosexuality. Below we will make a brief review of the main proposals that have taken place, from psychoanalysis to genetic and psychosocial theories.

1. Psychodynamic theories

For Freudian psychoanalysis, psychic structuring is strongly linked to psychosexual development . Sexual definition is a process that is not determined by anatomical characteristics, but by the predominant sexual identification and psychic choice of an object of desire. Homosexuality in this case is representative of a structuring in which a fixation on the maternal figure has taken place in opposition to the paternal figure.

This leads to the structuring of an object of desire that in this case corresponds to the same sex . This process does not necessarily occur in the same way in men and women. In this context, Freud used the term “inverted” to refer to homosexuality, in an attempt to establish a difference with the commonly used term “pervert”.

2. Biological determinism and genetic theories

Perhaps the theories that have generated the greatest impact in studies on homosexuality have been those that are inscribed in biological paradigms . These range from Darwinian evolutionary theories to those that suggest that homosexuality is the consequence of certain genetic factors.

Based on the above, it is often thought that homosexuality is counterproductive for the reproduction of the species, so some research suggests that it is necessary to review this interpretation, since the principle of natural selection does not necessarily apply in the case of hetrosexuality-homosexuality .

According to some of these theories, there is a possibility of a significant increase in fertility in women with a homosexual maternal family. They have also suggested that genetic factors that are related to the X chromosome influence men’s homosexual orientation.

3. Endocrine theories

The above and following explanations include research and theories on endocrine activity. These suggest that homosexuality is a consequence of peri or postnatal hormonal development ; which in turn may be caused by different elements, for example the mother’s hormonal treatments during pregnancy.

These theories also tend to emphasize the role of testosterone in the development of the brain and nervous system . This hormone may cause animals to become masculine, especially during the gestation period. Testosterone deficiencies in perinatal development in men may lead to male homosexuality, and high levels of the same hormone may lead to female homosexuality. There are even theories that suggest that the latter is visible in the size of the fingers of the right hand; that is, depending on which finger is larger than the other, the hand could be an indicator of homosexuality.

Finally, and on gestational development, it has been proposed that sexual orientation is related to the immune response of the mother’s body , which in turn relates to development and Y-chromosome activity (these theories apply when dealing with the male). Recent research has suggested that a certain reaction by the mother’s body to proteins associated with that chromosome would increase the likelihood that the male would be homosexual, as well as various medical complications.

4. Neurobiological theories

In the 1990s, the American neurobiologist Simon Levay carried out various studies in which he compared the brain structures of homosexual men and heterosexual men .

In an attempt to stop discrimination against gay men (he was gay), the neurobiologist offered a series of answers that are still valid and debated to this day.

According to their studies, there is a difference in the hypothalamus between heterosexual and homosexual men. It is a nodule that is in charge of the regulation of the endocrine system, which in the case of homosexual men presents similarities with the brain of heterosexual women. In addition to this research, different theories have been added which suggest, for example, neurobiological differences in the development of men and women.

5. Biological diversity and sexual dissent

In the context of the opening up of different scientific and philosophical currents, and consequently of different social movements that advocate the recognition of sexual diversity, queer theory has emerged. The latter assumes that both gender and sex are social constructions (and therefore sexual orientation in broad terms is also social constructions). As such, these constructions generate a series of norms, desires and possibilities of action; as well as practices of exclusion, segregation and pathologization .

In this same context, the biologist Joan Roughgarden has taken up Darwinian theories on sexuality, but to turn them around. Her research suggests the existence of different sexual genders, and questions the existence of a binary sex-gender (that is, the one that is reduced to the possibility of being a man or a woman giving primacy to heterosexuality). The latter is visible not only in human beings but in many intersex animal species and species that have the possibility of changing their biological sex throughout their lives.

6. Homosexuality in other species

In the late 1990s, Bruce Bagemihl theorized about sexual behavior in animals and proposed that, contrary to popular belief, such behavior takes different forms, even among animals belonging to the same species. From his research he reports that the homosexual behavior of animals is visible in more than 500 species ; ranging from primates to worms, including birds and mammals of different ecosystems.

Such behaviour includes copulation, genital stimulation and generally sexually displaying behaviour between animals of the same sex. The same author discusses the evolutionary functions of homosexuality and proposes that they cannot be the same for all species. The criticisms made of this research go in the same direction, that of finding reproductive and evolutionary benefits of sexual diversity from the biological paradigms; which can also have repercussions on its disqualification.

Bibliographic references:

  • Bagemihl, B. (1999). Biological Exuberance: Animal Homosexuality and Natural Diversity. St. Martin Press: USA.
  • Skorska, M., Blanchard, R., Vanderlaan, D. P. & Bogaert, A. F. (2017). Gay male only-children: evidence for low birth weight and high maternal miscarriage rates. Archives of Sexual Behavior, 46: 205-215.
  • Iemmola, F. & Camperio Ciani, A. (2009). New evidence of genetic factors influencing sexual orientation in men: female fecundity increase in the maternal line. Archives of Sexual Behavior. Springer Netherlands, 38: 393-399.
  • Mattioli, G. (2009). Psychoanalysts in the face of homosexuality. Retrieved July 6, 2018. Available at
  • Lantigua, I. (2005). When homosexuality was considered a disease. Recovered July 6, 2018. Available at
  • Roughgarden, J. (2004). Evolution’s Rainbow: Diversidad, género y sexualidad en la naturaleza y la gente. En rústica: Los Ángeles, California.
  • Adkins-Regan, E. (1999). Biological Exuberance: Animal Homosexuality and Natural Diversity. Bioscience, Oxford. 49(11): 926-82.