The sexual orientation of most people is heterosexual: their romantic interest is in individuals of the opposite sex. However, a notable percentage of people, usually around 5-10%, have a homosexual sexual orientation. Why does this happen? What is the phenomenon of homosexuality ultimately due to?

The search for answers has always been clouded by prejudices and misunderstandings, such as the belief that homosexuality is a disease that can be cured or a lifestyle choice. The first attempt to rationally approach the phenomenon was based on the idea that sexual orientation in humans is shaped in childhood through upbringing and social environment. This view is the most widespread nowadays.

However, the recent development of biology and neuroscience has allowed for a completely different approach. Homosexual individuals, during their embryonic life and immediately after birth, experienced an unusual endocrine environment, which led not only to their particular sexual orientation but also to differences in behavior and physiology. According to Jacques Balthazart, author of the book and a leading proponent of this particular view, homosexuality is not a matter of choice, it is not a disease or a disorder, nor is it due to indifferent parents or a problematic social environment. It is yet another manifestation of biological diversity.