Man's sexual orientation predetermined

A man's sexual orientation appears to be determined in the womb, a new study suggests.

Past research by Dr. Anthony F. Bogaert of Brock University in Ontario and colleagues has shown that the more older brothers a man has, the more likely he is to be gay. But it has not been clear if this is a prenatal effect or a psychosocial effect, related to growing up with older male siblings.

To investigate, Bogaert studied 944 gay and straight men, including several who were raised with adopted, half- or step-siblings or were themselves adopted. He reasoned that if the relationship between having older male siblings and homosexuality was due to family environment, it would be seen whether or not a man's older brothers were biological or adopted.

Bogaert found that the link between having older brothers and homosexuality was present only if the siblings were biologically related -- this relationship was seen between biological brothers who were not raised together. The amount of time that a man was reared with older brothers had no association with sexual orientation.

"These results support a prenatal origin to sexual orientation development in men and indicate that the fraternal birth-order effect is probably the result of a maternal 'memory' for male gestations or births," Bogaert writes in his report in PNAS.

A woman's body may see a male fetus as "foreign," Bogaert explains, and her immune response to subsequent male fetuses may grow progressively stronger.

"If this immune theory were correct, then the link between the mother's immune reaction and the child's future sexual orientation would probably be some effect of maternal anti-male antibodies on the sexual differentiation of the brain," he suggests.

(Agencies)

一项最新研究认为，男性的性取向可能在娘胎里就已经决定了。

加拿大安大略省布鲁克大学的安东尼·F·博格特博士和他的同事过去对男性性取向问题进行过研究。研究结果显示：男孩子的哥哥越多，他成为同性恋者的几率就越大。但有一点不能确定，“与哥哥一起长大影响男性性取向”是先天因素还是受后天心理影响？

为了研究这一问题，博格特对944名男性同性恋和异性恋者进行了调查，这其中包括几名自己或者兄弟是被领养的、与兄弟有一半或无血缘关系的男性。博格特认为，如果哥哥影响弟弟的性取向是受家庭环境影响，这就要看哥哥是亲生的还是领养的。

博格特发现，只有弟弟和哥哥之间有血缘关系时，弟弟才会受影响成为同性恋，即使他们不在一起长大，这种影响也存在。而且，与哥哥一起长大的时间长短与性取向没有什么联系。

美国国家科学院院刊刊登了博格特这一调查报告，报告中写道，“这些研究结果证明了男性的性取向由先天因素决定，同时暗示，哥哥影响未出生弟弟的性取向，可能源于怀孕妈妈对男婴的生理记忆。”

博格特解释说，也许母体将男性胎儿视为“异物”，因此怀孕妈妈的免疫体系对后来的男性胎儿反应越来越强。

博格特提出：“如果这个免疫理论正确，那么妈妈的免疫反应影响孩子将来的性取向可能是因为妈妈分泌的反男性抗体影响了胎儿大脑中决定性取向的机制。”

Vocabulary:

sexual orientation:性取向

womb : 子宫

prenatal: existing or occurring before birth（出生前的）

sibling: 兄弟姐妹

biological: related by blood（有血亲关系的），例如：the child's biological parents（孩子们的亲父母）

immune: 免疫的