Genetic Influences on Male Homosexuality

Abstract

Sexual orientation, identity and desire is the final product of complex interactions between factors such as genetic influences, epigenetic, developmental pathways, both prenatal such as sex hormones, including the maternal factors acting on the foetus, and postnatal factors including shared environmental influences such as family education, social and cultural influences, and nonshared environmental influence such as unique personal experiences. Male homosexuality poses an evolutionary dilemma as it entails reduced fitness but is nevertheless, in part, influenced by genetic factors. Examining the causes of homosexuality the author investigates the Darwinian dilemma as to why genetic factors that influence homosexual nonreproductive behaviour can be maintained in the population without disappearing as expected. Sexually antagonistic selection can explain male homosexuality. A sexually antagonistic model with genetic factors partially linked to X chromosome by increasing fecundity in females and influencing homosexuality in males could be selectively balanced in the population and explain all the peculiarity of male homosexuality. Key Concepts: Homosexuality is a volatile concept that varies with culture, history and traditions. Besides a difficulty in its definition even assessing its distribution across populations poses problems of reliability still unresolved. Basically, we still cannot claim that we know the actual distribution of human homosexuality. The homosexual phenotype is a complex set of emotion, behaviour and feelings influenced by a multiplicity of factors, environmental, developmental and genetic. The search of a single cause to explain the whole complexity of human homosexual phenotype seems arrived to an end. In homosexuals, genetic influence interacts with a multitude of environmental, familiar, early experiences or prenatal effects such as hormonal influences, stress or immune reactions by the mother, and other biological factors such as genomic, zygotic drive and epigenetics. Kin selection and avuncularity is a possibility that could compensate for the reduced fecundity of homosexuals, but most researches did not find any evidence of specific homosexual behaviour in modern society, which could promote close kin fecundity. The partial influence of genetic factors on homosexuality poses an interesting Darwinian conundrum which might be resolved by a sexually antagonistic selection mechanism. A sexually antagonistic selection mechanism suggests that the reduced fecundity of male homosexuals is balanced by the effect of the same genetic factors that promote fecundity in the maternal line females, thus balancing the effects on fitness and maintaining male homosexuality in the population.