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The differing sexual orientation of identical twins is an opportunity to investigate one of science’s most controversial questions, are people born gay?
Two brothers are identical twins, they were raised together, and as they grew up they remained physically similar, but their tastes and interests began to diverge. One became interested in dance and academia, while the other preferred sports. The most surprising difference between the brothers is that one is gay. They were raised by the same parents in the same household, sharing the same environment at a crucial time in their personal development.
In the general population the chance of someone being gay is less than 5%, unless you have a gay twin, here the chances are much higher. If you’re fraternal sharing half your genes, there’s nearly a 25% chance that you will also be gay. If you’re identical sharing all your genes, there’s roughly a 50% chance that you will also be gay. This suggests that there must be some genetic component to our sexuality. However, it can’t be all down to genes, otherwise all identicals would be either both be gay, or both straight. Some other factor must be at play.
In their first few weeks all foetuses develop along similar lines, if nothing changed we would all be born female. Foetuses with the male Y chromosome will form testes at about week 6, then begin to produce the hormone testosterone, but at about the 8th week testosterone is released and may affect early brain development. This hormone masculinises the body, testosterone also masculinises the brain, including a part called the hypothalamus, part of the network which controls who we find sexually attractive. Some scientists believe that the more the hypothalamus is exposed to testosterone, the more it sets the stage for a sexual inclination towards women.
Occasionally a male fetus may not produce sufficient testosterone or its brain does not absorb enough to shape it along heterosexual lines, if this theory is right , then it may be that the gay brother absorbed enough testosterone to masculinise his body, but not enough to fully differentiate his brain. As a result he was left with a desire for men.
Although there are still many mysteries twins like these are playing a crucial role in informing scientists about how and when we all develop our sexuality
Clip from the documentary “In the Womb: Identical Twins”.
Watch it here - http://youtu.be/7-dVvo7zbAU
After the success of In the Womb, which followed the development of a single foetus from conception to birth, comes In the Womb Multiples. This film series opens up the incredible foetal world of twins, triplets and quads in the womb. Using revolutionary 4D scans, we witness unique footage of multiple foetuses interacting with each other before birth. Multiples tells us not only about the extremes of human reproduction but the limits of human design.
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