It turns out that men with more older brothers have a higher rate of same-sex marriage

In recent years, laws on same-sex marriage have been enacted in countries around the world, and much research on sexual minorities has been conducted. Meanwhile, an Australian research team announced the results of a study that 'men with more older brothers have a higher rate of same-sex marriage.'

Are Sibship Characteristics Predictive of Same Sex Marriage? An Examination of Fraternal Birth Order and Female Fecundity Effects in Population-level Administrative Data from the Netherlands: The Journal of Sex Research: Vol 0, No 0

https://doi.org/10.1080/00224499.2021.1974330

Research confirms men with older brothers are more likely to be gay, suggesting same-sex attraction has a biological basis
https://theconversation.com/research-confirms-men-with-older-brothers-are-more-likely-to-be-gay-suggesting-same-sex-attraction-has-a-biological-basis-172396

Many studies have been conducted to investigate the causes of sexual orientation such as homosexuality, and various factors such as hormones and heredity are being investigated. 'If you gave birth to a boy, remaining in the body of the protein boy was generated by his mother, then born influence the sexual orientation of the child' is in such research the theory that those cast there is also. However, it is said that the research that advocates this theory has not been verified for a large number of subjects. Therefore, the research team analyzed the relationship between the number of siblings and sexual orientation using data from 9 million Dutch people born between 1940 and 1990.

The analysis found that a man with one older brother was 12% more likely to marry the same sex than a man with one older sister and 21% more likely than a man with one younger brother or sister. It was also found that men with three older brothers were 41% more likely to have same-sex marriage than men with three older sisters and 80% more likely than men with three younger brothers.

In the graph below, the horizontal axis shows 'how many of 1000 men got married with the same sex', and the vertical axis shows 'the composition of brothers and sisters'. In addition, orange is a graph of 'one brother and sister', blue is a graph of 'two brothers and sisters', and gray is a graph of 'three brothers and sisters'. If you look closely at the graph for each color, it is divided by 'where was the same-sex married man among the brothers and sisters?' From the tendency of the graph, it can be seen that the rate of same-sex marriage is basically higher for 'many older brothers and older sisters', 'having siblings instead of sisters', and 'closer to the youngest'.

From this analysis result, the research team concludes that the 'number' and 'gender' of siblings have a great influence on sexual development, and the above-mentioned theory that 'protein produced by boys remains in the mother's body' It says it will reinforce.