Homobadual men have, on average, a greater number of older siblings compared to their heterobadual counterparts.
>> Read more news about trends
The pattern, known as the effect of fraternal birth order, is not new to scientists, but researchers at the Brock University of Canada the University of Toronto and the Harvard Medical School now believe they have a biological explanation.
According to the study, published in the journal PNAS On Monday, maternal antibodies in the uterus may play a role in the process.
Researchers believe that when a woman becomes pregnant with her first child, a protein linked to the male Y chromosome (which only occurs in men) enters her bloodstream.
Your body then creates antibodies, because it recognizes the protein as a foreign substance.
With every male baby the woman has, the accumulation of antibodies increases. In high concentrations, it is possible for the antibodies to enter the brain of the second male fetus.
>> Related: Black, gay and proud: the search for a man to thrive
"That can alter the functions in the brain, changing the direction of how the male fetus can develop more His sense of attraction is late, "said study author Anthony Bogaert of Canada's Brock University, CNN .
To test this, the scientists collected blood samples from 142 pregnant women and tested them for antibodies against the brain protein known as NLGN4Y (also produced only in men).
Here's what they found:
- Mothers of homobadual children with older siblings had the most increased levels of antibodies against the protein.
- Mothers of homobadual children without older siblings had the second highest level of antibodies against the protein.
- Mothers of heterobadual children had lower levels of antibody s.
- Mothers without children had the lowest level of antibodies.
Bogaert and his team have been exploring the subject for more than 20 years and have found that the pattern exists in all cultures.
In a research project 10 years ago his team of psychologists and immunologists tested the reactivity of antibodies against two exclusively male proteins in 16 women without children, 72 mothers with heterobadual children, 31 mothers with homobadual children and not older brothers, 23 mothers of homobaduals, children with older brothers, and a control group of 12 men.
This research showed the immune response to proteins and found that mothers of homobadual children, especially those with older siblings, had significantly higher antibody concentrations than the other women.
But psychologists warned that the effects were modest and even if a boy has multiple siblings, the likelihood of that child being homobadual is still small.
"The implications of this study [new] and especially if and when it is replicated by an independent team, are profound," Bogaert said in a university press release . "In addition to understanding more deeply the exact origin of the older brother, it helps to solidify the idea that, at least in men, there is a strong biological basis for badual orientation" and "adds to the growing scientific consensus that homobaduality does not it's an option, but rather an innate predisposition. "
But, he added, although the investigation is getting closer to finding a mechanism, "I would not say that we have solved the puzzle of the effect of the fraternal birth order."
© 2017 Cox Media Group.