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Male sexual activity depends on the "female" X chromosome
Last reviewed: 01.07.2025
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Sexual behavior in the stronger sex does not necessarily depend on hormones: it is possible that some parts of the “female” X chromosome directly determine the sexual activity of men, bypassing hormonal mechanisms.
The difference between a man and a woman is determined by the hormonal balance - this is a known fact. If the child is male, then from the fourth week of pregnancy the fetus will be treated with testosterone. The level of hormones is determined by sex chromosomes, but to what extent do these chromosomes influence behavior? The answer would seem obvious: male hormones also shape male behavior. But scientists from the University of Virginia (USA) came to the conclusion that in this matter, hormones are not everything.
To find out the role of sex chromosomes in the formation of behavior, scientists transferred genes that determine male sex from the Y chromosome to a regular, non-sex chromosome in mice. This mutation allowed them to obtain males with two X chromosomes. XX males produced the same testosterone as regular XY males, but, surprisingly, their behavior was more “masculine”: they were more active in searching for females and had sex more often. From this, the researchers concluded that male behavior does not depend on testosterone levels and is most likely controlled by the X chromosome.
To confirm this, the scientists compared normal XY males with XXY males. Although in men the extra X chromosome leads to the development of Klinefelter syndrome, in mice such males also demonstrated intense "male" behavior. It should be emphasized that in this case the researchers focus on behavior, not on the appearance and physiology of the animals. How this data relates to human physiology and behavior, time will tell. However, it is worth mentioning that XXY males exhibit greater sexual activity than men with a normal set of sex chromosomes.
There is a hypothesis that the X chromosome in men exhibits moderate activity: according to some estimates, about a quarter of the genes in the male body are active. In this case, it is easy to assume that these genes are responsible for sexual behavior in men, and an additional copy of the X chromosome makes this behavior even more pronounced, although it has to contend with a less than ideal hormonal background. But to finally confirm this theory, it is necessary, of course, to identify a section of the X chromosome that, bypassing hormones, affects sexual activity.