The Science of Gay


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The Science of Gay

Here are a few really cool peer reviewed findings about the genetics of gay folks.

Homosexuality is Everywhere

● Around 10% of the human population is gay
● There is no firm consensus, estimates range from 3.4% to 20% of the population is gay

● Homosexual behavior has been observed in 1,500 animal species
○ Dwarf chimpanzees
■ The entire species is bisexual
○ Lions
■ To ensure loyalty, male lions often have sex with each other, strengthening bonds
○ Ducks and geese
■ Mate for life
■ 4-5% of goose and duck couples are gay
○ (Other gay animals)
■ Penguins
■ Dolphins
■ Bison
■ Giraffes

Can Hormone Exposure Before Birth Help Determine Whether Someone Will Be Born Gay?

Spatial Judgment
Research suggests early exposure to hormones, such as testosterone, in the womb contributes to this ability

On Average, in Regards to Spatial Awareness:
• Men were better at matching angles than women
• Gay men scored worse than straight men
• Lesbians scored better than straight women

Digit Ratio
The “Digit Ratio” was associated with spatial judgment ability

The length of a person’s fingers may indicate their sexual orientation
● Digit ratio between index and ring finger are thought to be affected by the amount of testosterone exposure in the womb. Higher levels of testosterone are associated with a shorter index finger relative to the ring finger.
● The shorter your index finger relative to your ring finger, the more testosterone exposure.
○ Gay men and Straight women are more likely to have a longer index finger (relative to ring finger)
○ Lesbians and Straight men are more likely to have a shorter index finger (relative to ring finger)
○ Studies have shown both hyper masculine ratios as well as feminine ratios in gay men

○ According to a study by Dennis McFadden, a psychology professor at the University of Texas at Austin
— Gay men are 31% more likely to be left-handed than heterosexual men
— Lesbians are 91% more likely to be left-handed than heterosexual women

A surge in prenatal testosterone can make you tougher on the field
● A study of college varsity athletes showed that they had shorter index fingers than other students

Hair Whorl
Yes, seriously, it’s spelled whorl
● Can you tell if someone’s gay by the direction of their hair whorl?
● Why? – The gene that controls the direction in which hair grows may be linked to left-handedness and sexual orientation
● In one survey, 23% of gay people had counterclockwise hair whorls
○ In the general population, only 8% have counterclockwise hair whorls

Birth order may be a factor in determining sexual orientation
● Having older brothers may increase the likelihood that a man will be gay
○ Older sisters don’t have an effect, and it doesn’t matter if the brothers grow up in the same home
● 15% of gay men can attribute homosexuality to their birth order according to research by Ray Blanchard and Anthony F. Bogaert of the University of Toronto
○ The odds of a man being gay increases by 33% for every additional older brother that he has

Why would birth order be a factor?
○ A study published in The Quarterly Review of Biology suggests that epigenetics are the biological driving force behind sexual orientation.
○ Epigenwazzit?
■ Let’s explain. Epigenetics are inheritable factors that regulate DNA, switching genes on and off
○ Epigenetic changes have evolved to benefit adults but are sometimes passed to their children. Epigenetics may be responsible for the response in mothers of multiple sons
■ After giving birth to sons, the mother’s body may fight the production of another male by “feminizing” sexual orientation
■ Inherited epigenetic markers may explain why homosexuality seems to sometimes run in families, despite the lack of a “gay gene” confirmation

Twin Brothers
This study found that gay men share genetic signatures on part of the X-chromosome: Xq28
● In a study of 400 sets of twins, researchers at Northwestern University have found gene markers that may contribute to sexual orientation
■ This study found that gay men share genetic signatures on part of the x-chromosome: Xq28

Brain Scans
Gay men and heterosexual women – the two halves of the brain are more or less the same size
Lesbians and heterosexual men the right hemisphere of the brain is slightly larger
“This is yet another in a long series of observations showing there’s a biological reason for sexual orientation” — Dean Hamer, a molecular biologist at the National Institutes of Health (NIH)

While there have been no studies to conclusively say what determines sexual orientation, it is widely accepted in the scientific community that genetic and developmental factors both play a role.

When did they decide to be gay?
When did YOU decide to be straight?
 Exactly. Genetics had a role to play.
And frankly, it’s none of your business anyways.

The Science of Gay


Birth Order:
Birth Order:
Digit Ratio:
Twin Brothers:
Gay Animals:
Hair Whorl: