Scientists have confirmed the legality of the use of a new method of American researcher Tatyana Jovanovi, which allows to estimate the influence of “older brother effect” on homosexuality men. A simple mathematical analysis allows to separate the influence of homosexuality in the presence of his older brother and family size in General. A meta-analysis of ten studies using the new approach showed that the presence of one older brother increases the probability to be born gay by 38 percent, while the number of younger brothers is not associated with homosexuality. The method of Jovanovi probably cannot be used to evaluate the Association of the presence of the sons of gays and the total number of children in women. A study published in the journal Proceedings of the Royal Society B: Biological Sciences.
The “older brother effect” is that men who have older brothers are more likely to become homosexuals. A possible explanation of this phenomenon is the immunological foetus in the womb will allocate specific male antigens, including the surface of neurons, and they get into the circulatory system of the mother. The immune system reacts to foreign particles and creates antibodies. During next pregnancy, these antibodies are associated with “masculine” molecules on the surface of neurons and do not allow those to develop. In the result grows, the probability that person then will attract men, not women. This hypothesis was tested in only one study, but the results confirmed it.
Another phenomenonassociated with homosexuality — gay men mothers give birth to more children. This is explained by the hypothesis of balancing selection. The fact that homosexuals produce much less offspring, than heterosexual men. If you add this with the assumption that homosexuality is partially inherited, it turns out that the number of gays in the population should steadily decrease. In this case, if the same genes that are associated with homosexuality, increase fertility of women, the balance would be restored.
The complexity of the study of these two phenomena is that they are closely related. The sons of women who give birth to many children, more older brothers. Conversely, the fact that there are gay brothers, impact on the analysis of the number of children their mother. To overcome these limitations, chovanova Tatiana (Tanya Khovanova) from the Massachusetts Institute of technology have developed a simple mathematical method. She compared three different size: the probability that an only child in the family turns out to be gay (p11); that the first (p12) or second (p22) of the two boys in the family are homosexuals. Thus, if p12> p11, the mothers of gay men tend to have more children. But if p22> p12, the presence of older brother increases the probability of men being born homosexual.
Jovanovi the method has its limitations: first, it analyzed only families in which one or two sons. Because of this, a significant part of the population remained outside of the sample. Secondly, I wonder could we apply the obtained results to the third and subsequent boys in the family.
To extend the application of the method of Jovanovic and check its legitimacy, ray Blanchard (Ray Blanchard) from the University of Toronto and his colleagues conducted a meta-analysis of data from ten studies that included a total of 5390 people. Researchers have calculated what percent of the data is lost when only families with one or two sons and checked whether the amount of unaccounted for data on the result of the analysis.
When selecting families with one and two sons from 12 to 68 percent of the population was excluded from the analysis. The non-revenue data did not affect the correlation between having older brothers and sisters likely to be gay.
The presence of one elder brother at 38 percent increased likelihood of men to be born gay (p = 0.0008). This number, which is calculated by the method of Jovanovic, coincided with the estimates of other studies. Consequently, the approach can be applied for further analyses, including families with multiple children.
The authors did not find an influence of the presence of a gay man on family size, even in the analysis of data for the work in which such effect was noted. In other studies this correlation was both positive and negative or neutral. However, the number of not sampled for the method Jovanovi people were correlated with the results. Probably, the exclusion from the analysis of families with more than two children or parents of girls are significantly affect the result, and this method is not applicable to issues related to family size.
A few years ago there was an article stating that the “older brother effect” occurs because the immune response of the mother to the proteins of the brain of her older sons. And in this the text can be read whether homosexuality with genes, as it is influenced by hormones and immunity, as well as how it can be explained from the point of view of the theory of evolution.