Epigenetic theories of homosexuality

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Epigenetic theories of homosexuality concern the studies of changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence, and their role in the development of homosexuality.^[1][2][3] Epigenetics examines the set of chemical reactions that switch parts of the genome on and off at strategic times and locations in the organism's life cycle. However, epigenetic theories tangle a multiplicity of initiating causes and resulting final effects and will never lead to a single cause or single result. Hence, any interpretation of such theories may not focus on just one isolated reason of a multiplicity of causes or effects.^[4]

Instead of affecting the organism's DNA sequence, non-genetic factors may cause the organism's genes to express themselves differently. DNA in the human body is wrapped around histones, which are proteins that package and order DNA into structural units. DNA and histone are covered with chemical tags known as the epigenome, which shapes the physical structure of the genome.^[5] It tightly wraps inactive genes on the DNA sequence making those genes unreadable while loosely wrapping active genes making them more expressive. The more tightly wrapped the gene, the less it will be expressed in the organism. These epigenetic tags react to stimuli presented from the outside world. It adjusts specific genes in the genome to respond to humans' rapidly changing environments. The idea of epigenetics and gene expression has been a theory applied to the origins of homosexuality in humans. One team of researchers examined the effects of epi-marks buffering XX fetuses and XY fetuses from certain androgen exposure and used published data on fetal androgen signaling and gene regulation through non-genetic changes in DNA packaging to develop a new model for homosexuality.^[6] The researchers found that stronger than average epi-marks, epigenomes that are wrapped tightly around the DNA sequence, convert sexual preference in individuals without altering genitalia or sexual identity.^[7] However, a later study found that male homosexuality is not linked to low androgen sensitivity or "sex-reversed" epi-marks.^[8]