A team of researchers from the University of Toronto and the University of Lethbridge has found evidence showing that men with an older brother are more likely to be gay than men who do not .
In his study , published in the journal Proceedings of the Royal Society B , he comes to provide more data on the reasons, still unknown, for the origins of homosexuality.
Question of antibodies?
The cited study analyzed data from 10 unrelated studies that included sexual orientation for 5,400 men and also information from siblings, finding that those with an older brother were 38 percent more likely to be gay than those without a sibling. higher.
They also found that the more older siblings a man had, the more likely he was to be gay – having three older siblings, for example, doubled the odds that a man was gay.
But the same could not be said of women. The researchers could not find any pattern in siblings, male or female, that changed the likelihood that a woman was homosexual.
The researchers were unable to determine why birth order affects the likelihood of being homosexual, but they suggest that the mother’s immune response to having a male child may have a later impact on babies born thereafter.
The theory, called the maternal immune hypothesis , suggests that when a woman gives birth to a male baby, her body produces antibodies in response. The theory then suggests that the antibodies produced remain in the female body and somehow reach the brain of future male babies .