Alternative Sexual Orientation in Humans: What Is Known and What Needs to Be Known Further

ABSTRACT

Since the 20th century, multiple studies have linked the variations in human sexual orientation, from heterosexuality to bisexuality or homosexuality, to a wide range of biological factors. However, a clear mechanism that leads to the development of these variations has not been established yet. This review consolidates various comprehensive studies on the possible biological factors in the fields of genetics, epigenetics, uterine environment, hormones, neuroanatomy, and neurobiology that lead to these variations. One intriguing question that ‘homosexuality phenotype’ faces is its ability to avoid elimination by Darwinian selection. This review tries to explain why natural selection is not eliminating the genetic factors associated with homosexuality even at the cost of the evolutionary fitness of homosexual individuals. Studies supporting certain strong candidates for alternative sexual orientation (ASO) are highlighted, which can become new research avenues for investigators in this field. Further, a novel speculation is proposed that might be contributing to the development of variation in human sexuality.

KEYWORDS:

• Alternative sexual orientation (ASO)
• homosexuality
• bisexuality
• gay
• prenatal stress
• genetics
• epigenetics
• hormones
• neuroanatomy

Acknowledgments

We would like to sincerely thank Prof. S. Basu-Modak from the Department of Zoology, University of Delhi, for guiding us at various points during the preparation of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.