We may know why younger brothers are more likely to be gay | New Scientist

Contents:

• MEN WH OLR BROTHERS ARE MORE LIKELY TO BE GAY, STUDY SUGGTS
• IS A PERSON ‘BORN GAY’, OR IS BEG GAY A LEARNED BEHAVR?
• WE MAY KNOW WHY YOUNGER BROTHERS ARE MORE LIKELY TO BE GAY
• ARE YOUNGER BROTHERS MORE LIKELY TO BE GAY?
• GAY GEICS
• NEWS & TECHNOLOGYTHE BLOGY OF BEG GAY
• THE LAMBDA: ALL THGS GAY & FRATERNAL
• YOU’RE NOT BREAKG BARRIERS BY BEG GAY A ATERNY
• GAY HISTORY OF MEN’S FRATERNI
• GENR NONNFORMY AND BIRTH ORR RELATN TO ANAL SEX ROLE AMONG GAY MEN

MEN WH OLR BROTHERS ARE MORE LIKELY TO BE GAY, STUDY SUGGTS

Men wh olr brothers are more likely to be gay, acrdg to a study published Wednday the journal Proceedgs of the Royal Society B. This new report builds upon prev rearch regardg male birth orr and homosexualy, though there is still no cisive ncln as to why there’s a lk between the cross-analyzg data om 10 scientific studi wh more than 5, 000 subjects, rearchers found that men wh olr brothers were 38 percent more likely to intify as gay. ”The study, which pared the probabily of the youngt brother a two-son fay beg gay as pared to the olst son, did not clu female subjects, as prev rearch has tablished that women do not fluence the sexual orientatn of their younger siblgs, acrdg to this study did not terme a ncrete reason for the rrelatn between a man havg an olr brother and intifyg as gay, Blanchard said that “pots toward the need for more rearch on the 'maternal immune hypothis'” — a theory Blanchard troduced 1996 that suggts that a mother is exposed to “male-specific substanc” durg pregnancy wh or the birth of a son.

Acrdg to proponents of the theory, the mother’s immune rponse is changed durg the pregnancy of a boy, creasg the likelihood that a subsequent male child would be gay. If the DNA sequence were the only thg termg whether someone is gay or not, we would expect intil tws to match 100% of the time.

IS A PERSON ‘BORN GAY’, OR IS BEG GAY A LEARNED BEHAVR?

Of urse, this isn’t the only environmental explanatn for how people are born gay – there are plenty of men wh olr brothers who are not gay. This uld mean that there are some gen that are passed down om the mother’s si that make women more fertile and make men more likely to be gay. No matter why those gen are still around, we do know that beg gay is partly geic and partly termed before a baby is even born.

The more olr brothers a boy has, the more likely he is to be gay when he grows up – an effect lled the “aternal birth orr effect”. They found that the mothers of gay sons wh olr brothers had the hight levels of antibodi agast this prote, followed by the mothers of gay sons wh no olr brothers. “Given that the prote is known to be important synapse formatn, you n see how maternal antibodi might affect the wirg of the fetal bra, and that might expla why each subsequent son is more likely to grow up gay.

WE MAY KNOW WHY YOUNGER BROTHERS ARE MORE LIKELY TO BE GAY

“The signifince of this prelimary observatn, if n be replited, is that intifi specific molecul the bra that may be important for heterosexual as well as homosexual velopment, ” says Dean Hamer, a pneer of rearchg the blogil termants of sexual orientatn. In 1996, the psychologists Ray Blanchard and Anthony Bogaert published a paper ntendg that homosexualy was more mon men who had olr brothers. "In [Wtern] societi, homosexual men are femized at var levels and they have more olr brothers than heterosexual men, " state the thors of the study.

"To evaluate whether femy and the aternal birth orr effect are universal featur of male homosexual preference or not, we llected origal data om homosexual men, heterosexual men, and heterosexual women om Java (Indonia).

Consistent wh Blanchard and Bogaert's fdgs Wtern societi, they found that homosexual men were more likely to have olr brothers than heterosexual men. Intertgly, the rearchers also found that homosexual men were more likely to have olr sisters, although this difference was smaller than the olr brother difference. Usg standardized photographs of heterosexual and homosexual Indonian men, the rearchers found that men wh olr brothers were perceived to have more feme facial featur than men whout olr brothers.

ARE YOUNGER BROTHERS MORE LIKELY TO BE GAY?

The thors wre, "Taken together, the rults suggt the prence of a femizg factor associated wh male homosexualy that is partially termed by male birth orr. In a study where scientists looked at the sexual aroal patterns of intil tws wh different sexuali—specifilly, where one was gay and the other was straight—they found that gay tws monstrated more genal aroal rponse to same-sex imag, whereas straight tws monstrated more aroal rponse to oppose-sex imag [2]. In theory, this means two people uld rry “gay gen, ” but both of them wouldn’t necsarily be gay pendg on certa environmental factors.

It’s held aloft by Dr Alan Sanrs and a group of lleagu om NorthShore Universy near Chigo who are attendg a gay pri ftival. “The people participatg our study are terted ntributg to this kd of scientific knowledge and want to unrstand at least part of how they me to be the way they are, ” Sanrs search for ‘gay gen’ go back to 1993, when a US team led by Dr Dean Hamer scribed a regn of DNA loted on the X chromosome lled Xq28.

GAY GEICS

“Conservative, right-wg people hated bee they felt that was sayg that beg gay is like beg black, that was -born, that would somehow ‘exce’ gay people or give them more rights, ” says Hamer.

“On the other hand, gay people hated too bee, at that time, there were fears that the disvery would be mised to abort gay babi and wipe gay people off the face of the Earth. ”More like thisAlthough the fears rema, recent years the search for ‘gay gen’ has bee more accepted by the gay muny, no small part bee a blogil explanatn would unrme arguments that beg gay is a social or liftyle choice.

NEWS & TECHNOLOGYTHE BLOGY OF BEG GAY

For stance, intil tw brothers (siblgs rived om the same fertilised egg) are more likely to both be gay than aternal tws (tws that velop om separate eggs). The fact that intil tws have the same DNA and aternal tws share 50 per cent suggts that male homosexualy is gay geneIt was sctisg fay tre to see how homosexualy is hered that led Hamer to the disvery of Xq28. Now chief of the gene stcture and regulatn sectn at the US Natnal Cancer Instute, his study revealed a cur pattern: gay men tend to have more gay uncl and gay male s on their mother’s si of the fay than on their father’s.

This is bee mal her their X chromosome om their track down the DNA regn lked to the gay tra, Hamer ed a technique lled ‘lkage mappg’, an approach that lets geicists fd a gene even when they don’t know what do or where ’s loted. Lkage mappg works bee close relativ like brothers share not only a particular tra, such as homosexualy, but also the gen unrlyg the tra.

So, if you study many pairs of gay brothers and fd a DNA regn that’s the same more than 50 per cent of s, ’s likely to be lked to homosexualy. A subsequent study 1999 failed to replite Hamer’s rults and other rearchers are sceptil that Xq28 is lked to homosexualy at brothers, immune mothersMany scientists believe that exposure to hormon durg pregnancy heavily fluenc sexualy. Durg pre-natal velopment, for example, the sex ans a foet n regnise ttosterone, which will swch on gen to make om a few superficial differenc (among them penis and rg-fger length – both longer homosexuals), gay and straight men’s bodi appear the same.

THE LAMBDA: ALL THGS GAY & FRATERNAL

The exceptn is homosexual men’s bras, which show remarkable siari to the bras of heterosexual women, suggtg that sexual orientatn pends on the effect hormon have on the velopg the two factors only go so far explag how homosexualy velops. ”In 1996 Blanchard and Profsor Tony Bogaert revealed a peculiar phenomenon: the more olr brothers a boy has, the greater their chanc of beg homosexual. ”Blanchard believ that homosexualy is “100 per cent blogil”, and timat that the aternal birth orr effect acunts for 15-30 per cent of gay men the populatn.

YOU’RE NOT BREAKG BARRIERS BY BEG GAY A ATERNY

Fertile femalProfsor Andrea Camper Ciani at the Universy of Padova Italy has tted var hypoth by studyg 100 fai of gay men. Not only did he replite Blanchard’s birth orr effect, he also tected herance of homosexualy on the mother’s si, supportg Hamer’s ia of a gay gene on chromosome X. How would gen that e homosexualy pass om one generatn to the next, given that gay people reproduce ls than heterosexuals?

Natural selectn oppos anythg that might e even a small rctn the number of offsprg you produce, so a gay tra would soon disappear om the gene pool. After Camper Ciani scribed the observed patterns pedigre of homosexualy – the effects of maternal herance and birth orr – his dghter suggted that he re-check his data to see if the female relativ of gay men had more children on the mother’s si. “Mothers and nts on the maternal le of homosexuals had around one-fifth to one-fourth more kids than the heterosexual parison, and also than the paternal le.

GAY HISTORY OF MEN’S FRATERNI

In this stance, the ‘gay gen’ don’t exist to make men homosexual, stead they’re a nsequence of ‘fertily factors’ that help women reproduce. Nippl are another example of a sexually antagonistic tra: they’re need for feedg babi, but velopg nippl men is a waste of the body’s rourc and allow errors leadg to breast search for sexualyEven if Camper Ciani’s fecundy factors are the same as Hamer’s gay gen, don’t tell what the specific gen actually do.

Hamer speculat the gen might boost the size or nnectns om parts of the bra ed reproductn – such as the hypothalam – to make people more Sanrs’s study at NorthShore Universy uld fally reveal the inty and functn of ‘gay gen’.

GENR NONNFORMY AND BIRTH ORR RELATN TO ANAL SEX ROLE AMONG GAY MEN

Sanrs will then e sequenc om databas like the Human Genome Project to ppot which gen are the what happens if ‘gay gen’ are found?

While they may nfirm the ia that homosexualy has a blogil basis, many people fear that the rults uld be ed to discrimate agast gay people. “People we talked to at gay pri ftivals have signer-baby kd of worri – a geic tt employed a pre-natal way, or for employment and surance discrimatn, maybe the ary too. The fdgs, which parallel rults of an earlier study of gay mal, bolster the tentative but creasgly plsible theory that human sexual orientatn -- heterosexual as well as homosexual -- is fluenced to a signifint gree by blogy and is not exclively a matter of upbrgg or "liftyle choice.

" The study of lbian tws "is the largt ever of female sexual orientatn, and suggts that geic factors are as important termg lbianism as they are fluencg male homosexualy, " said psychologist J. By g ads the gay media, Bailey and Pillard loted 147 lbians, cludg 115 who had tw sisters and 32 wh adoptive sisters.