If homosexual men have less chances of siring offspring, why has there been a stable presence of homosexuals over time?

According to a study by Dr. Giorgi Chaladze, it is likely that the "gay genes" are present in half of the population - both men and women - who are heterosexual or "straight".

The Ilia State University research used a computational study in an attempt to determine how much of the genes have to be in the gene pool to exist today. His curiosity was piqued by the fact that homosexual men have five times fewer children than straight men yet the homosexual population continues to grow.

Dr Chaladze used an individual-based genetics model to come up with his findings, the Daily Mail reported.

His findings, published in the Archives of Sexual Behaviour, explained that throughout history, homosexuality has maintained a low, persistent and stable presence. And for this to be possible, Dr. Chaladze calculated that at least half of straight men and women must be carrying the "gay genes" that are passed on to the next generations.

His research also indicated a trend where sisters of gay men had the tendency to bear more children and emphasized that men carrying these genes are not necessarily homosexuals.

Another interesting fact, according to the Independent, is that the number of men in same-sex relations are actually higher than those who identify themselves as homosexuals.  
The study, however, did not name a specific gene but the lead researcher took into consideration findings of previous researches in his calculation: that homosexuals tend to come from larger families, and homosexuality’s tendency to be inherited.

A 2014 study had concluded that homosexuality is heritable. DNA samples of 410 pairs of homosexual twins were examined and the researchers found that homosexual men have similar genetic markers in chromosome 8 and Xq28 region of X chromosome. A co-author of the study commented that a group of genes may be at play in homosexuality and not just a singular gene.

Canadian scientists also discovered that a male’s chances of becoming a homosexual increases by 30 percent if he has an older biological brother, and another 30 percent if he has more than one male sibling. The Telegraph wrote that the increase in chances could be related to the mother’s changing immune response to each child. MIMS

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