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Dear Christine, Another Question from WIWC

| April 4, 2016

ccc 2Dear Christine,

Another question:  What roles does epigenetics, genetics, other biological factors and environment play in the development of glbt sexual orientations?

Wondering in Washtenaw County

Dear Wondering,
Sexual orientation is a complicated biological and psychosocial construct and it cannot be explained by either one completely.  There is no “gay gene” though there clearly is some genetic component to sexual orientation. There is a significant role for epigenetics, which are the naturally occurring changes to a gene expression by age, the environment, lifestyle and disease.  This is how identical twins can start out with exactly the same DNA, and yet, over time, they can look quite different as they age and are exposed to different environments.  Epigenetics tells us that the environment, nutrition, stress, pollution, smoking, alcohol, drugs, childhood viruses and so on, could cause that gene to be expressed or switched on or not.  Identical twins are studied to get a better idea of epigenetics and sexual orientation.  In 47 male twin pairs, 37 of them had one who was gay, and in the other 10 pairs, both brothers were gay.  So, it’s not guaranteed that identical twins will both be homosexual.

There is evidence of “the older brother effect”  that the chance of a son being gay increases by 33% for each older brother ahead of him.  Researchers suspect several hypothesis, including one that the mom’s immune system reacts against male antigens and alter the later fetus’ development.  There does not seem to be anything similar going on for female fetuses developing into lesbians.  Epigenetics probably has some effect on how much testosterone is available to a fetus and how the fetus responds to that hormone, but we simply don’t know much about that yet.

Hormones play a role in sexual orientation but what would cause a change in hormone development (more testosterone in a female, more estrogen in a male, as a fetus, or a child in puberty) is not known.  It is possible that prenatal hormone therapy might be used to reduce the probability of homosexuality in female fetuses. But there are a lot of contingencies in that:   It is possible, if there is a probability.  How that could be assessed, no one knows.

We haven’t even begun to look at the genetic differences of children who are born with irregular genitalia such as someone with genitalia for both genders in one body, also called intersex!  Those people partially develop as both genders and eventually have to choose to get one or the other hormone and thus, choose their sex.  Psychosocial theories that early traumas in childhood, or sexual abuse created a change in sexual orientation or caused someone to become transgender.  This is not true at all.  There is a growing body of research that male to female transgender women have “a more feminized brain” starting in utero, with insufficient uptake of male hormones.  The brains of trans women’s white matter appears to be half way between those of biological male and female control groups.  Those parts of the brain are also shaped by performance and experience, so we don’t know whether nature or nurture is at work here.  A recent survey of identical twins found that 20% of cases had both twins turn out transgender, despite having identical DNA.

Identifying causes of sexual orientation and sexual identity is complicated, including genetic, hormonal, environmental and who knows what else!  Research continues.

Christine Cantrell, PhD


Email Me

Christine C. Cantrell, PhD
1026 W. 11 Mile Rd,
Suite C
Royal Oak, MI 48067



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