If you are a white male and have several older brothers, you have a better chance of being gay, according to a report discussed in
New Scientist magazine.
Researcher Ray Blanchard and his fellow scientists at the Centre for Addiction and Mental Health at the University of Toronto
have studied trends in homosexual indicators for years. Previously, they concluded gay men are more likely to be left-handed than
straight men and lesbians are more likely than gay men to have the same predilection.
Now, they say, the 'Big Brother Effect' affects 15 percent of all gay men.
Through statistical analysis, Blanchard found that the average man who has 2.5 older brothers is twice as likely to be gay as a
man with no older brothers. And a man with four older brothers is three times as likely to be gay. Other studies completed by other
researchers have shown similar results. John Manning at the University of Central Lancashire found the effect in all of his samples of
gay men, according to New Scientist. And University of California at Berkeley researcher Marc Breedlove also published similar
results.
Even animal studies seem to suggest similar results. Charles Roselli from the Oregon Health and Science University presented
new data at last year's Society for Neuroscience meeting. Roselli's research with sheep suggested about eight percent of sheep are
gay. Roselli said that the 'Big Brother Effect' even has some implications in his sheep studies. 'I'm seeing some hints of it,' he told
New Scientist.
Breedlove said that while none of these studies establish a cause and effect relationship, they provide a strong correlate to guide
other research. 'It's one of the few reliable correlates of homosexuality that I know of,' he told New Scientist. 'If you don't see it, you
start thinking maybe you've done something wrong.'
One of the cause-effect relationships under study is that of low birth weight. Boys with several older brothers tend to weigh less at
birth than would be expected. This is true of both gay and straight men, but gay men weigh even less on average. Strengthening the
'Big Brother Effect' is the data showing that firstborn gay men weighed the same as their straight counterparts.
Both Blanchard and Breedlove are interested in examining the chemical interactions between mother and fetus in utero. The
slight differentiation between male and female fetuses is the H-Y antigen. The mother's immune system often treats the fetus as a
foreign object and produces antibodies to the soon-to-be male fetus. Just like the immune system keeps track of viruses and other
foreign bodies that have ever been in the bloodstream, researchers say, a woman's immune system could keep track of the number
of male fetuses ever present in the body.
Further evidence comes in the form of larger placentas in later-born males. Oddly enough, studies suggest that more male
hormones are pumped into later born males in utero, another biological difference that researchers say could predispose a boy to be
gay.
The importance to the discussion of nature versus nurture comes in here because the findings remain the same whether a gay
boy grew up in the same household as his many older brothers or was raised separate from his brothers. Blanchard and Breedlove
argue that there is a strong argument here for nature over nurture.
When it comes to lesbians, researchers are at a loss. There appears to be no correlation between birth order and the eventuality
of a lesbian child.