Further evidence that genetics has a role in determining sexual orientation in men

Is sexual orientation something people are born with - like the colour of their skin and eyes - or a matter of choice?

Canadian scientists have uncovered new evidence which shows genetics has a role to play in determining whether an individual is homosexual or heterosexual.

The research was conducted by Dr. Sandra Witelson, a neuroscientist in the Michael G. DeGroote School of Medicine at McMaster University, and colleagues at Sunnybrook Health Sciences Centre in Toronto who studied the brains of healthy, right-handed, 18- to 35-year-old homosexual and heterosexual men using structural Magnetic Resonance Imaging (MRI).

About 10 years ago, Witelson and Dr. Cheryl McCormick, then a student of Witelson’s, demonstrated there is a higher proportion of left-handers in the homosexual population than in the general population – a result replicated in subsequent studies which is now accepted as fact.

Handedness is a sign of how the brain is organized to represent different aspects of intelligence. Language, for example, is usually on the left - music on the right.

In other research, Witelson and research associate Debra Kigar, had found that left-handers have a larger region of the posterior corpus callosum – the thick band of nerve fibres connecting the two hemispheres of the brain – than right handers.

This raised the hypothesis for the current study – whether the anatomy of the brain of the sub-group of right-handed homosexual men is similar to that of left-handers.

They found that the posterior part of the corpus callosum is larger in homosexual than heterosexual men.

The size of the corpus callosum is largely inherited suggesting a genetic factor in sexual orientation, said Witelson “Our results do not mean that heredity is destiny but they do indicate that environment is not the only player in the field,” she said.

While this is not a litmus test for sexual orientation, Witelson said this finding could prove to be one additional valuable piece of information for physicians and individuals who are trying to determine their sexual orientation. “Sometimes people aren’t sure of their sexual orientation.”

The researchers also undertook a correlational analysis which included size of the corpus callosum, and test scores scores on language, visual spatial and finger dexterity tests. “By using all these variables, we were able to predict sexual orientation in 95 per cent of the cases,” she said.

Source: McMaster University

Related stories:

Global AIDS prevention gives short shrift to gays
(AP) -- Jorge Saavedra's moment of truth came in the middle of an impassioned speech to 5,000 people about the paltry amount of money being spent to stop the spread of AIDS among gay men. The Mexican federal official paused, then said publicly for the first time that he was gay.
Homosexual behaviour due to genetics and environmental factors
Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world’s largest study of twins.
Homosexual behavior due to genetics and environmental factors
Homosexual behaviour is largely shaped by genetics and random environmental factors, according to findings from the world's largest study of twins.
Study shows male homosexuality can be explained through a specific model of Darwinian evolution
Reporting in this week's PLoS ONE, an Italian research team, consisting of Andrea Camperio Ciani and Giovanni Zanzotto at the University of Padova and Paolo Cermelli at the University of Torino, found that the evolutionary origin and maintenance of male homosexuality in human populations could be explained by a model based around the idea of sexually antagonistic selection, in which genetic factors spread in the population by giving a reproductive advantage to one sex while disadvantaging the other.
Study shows weight bias is as prevalent as racial discrimination
Discrimination against overweight people—particularly women—is as common as racial discrimination, according to a study by the Rudd Center for Food Policy & Obesity at Yale University.
Survey: Two-thirds of Illinois public schools provide comprehensive sex education
A study of sex education in Illinois public schools found that one out of three teachers did not meet a very forgiving definition of comprehensive instruction, researchers from the University of Chicago Medical Center report in the February 2008 issue of the journal Obstetrics and Gynecology.
Bisexuality not a transitional phase among women, according to new research
Bisexuality in women appears to be a distinctive sexual orientation and not an experimental or transitional stage that some women adopt "on their way" to lesbianism, according to new research published by the American Psychological Association.
In fruit flies, homosexuality is biological but not hard-wired
While the biological basis for homosexuality remains a mystery, a team of neurobiologists reports they may have closed in on an answer -- by a nose.

News discussion:

Medicine & Health news