Why Are Men Taller Than Women? Weirdly, We Don’t Actually Know

Men, on average, are about 13 centimeters (5 inches) taller than women, with sex hormones and growth genes thought to be the main drivers of this height difference. However, while numerous studies have sought to identify these male-specific genes, the long and short of it is that we still don’t really understand the genetic mechanisms underlying this size gap.

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What we do know is that hormones like testicular androgens play a massive role in causing men to become taller than women from puberty onwards. According to the authors of a new report, though, it’s currently unclear how the interplay between these sex hormones and genetic growth factors influences adult height.

Much of this uncertainty stems from the fact that all previous attempts to identify a male-specific growth gene on the Y chromosome – which is possessed only by the masculine sex – have proved unsuccessful.

To try and get the measure of things, the researchers cite two recent studies – one of which they themselves authored. Both papers focus on a growth-related gene known as SHOX, which is found on both the X and Y sex chromosomes and is therefore possessed by males and females.

As a result, SHOX has been largely overlooked as a candidate for the elusive masculine-only height gene. However, in their study, the researchers found that SHOX is expressed to a considerably higher degree in men’s tissues than in those of women.

This means that while the gene itself may not be exclusive to males, it is more active in men than in women, and might therefore represent the missing genetic cause of the increased stature of the masculine sex.

These findings are backed up by the second study, which examined height and genome data from 928,605 people. Of these, 1,225 had sex chromosomal aneuploidy, whereby they possess an atypical number of either of the sex chromosomes.

Tellingly, an extra Y chromosome was associated with an additional 3.1-centimeter (1.2 inches) height increase when compared to that produced by an extra X chromosome. Given that SHOX is the only skeletal growth-related gene found on these chromosomes, this discrepancy can only be explained by a difference in the expression of this gene.

The same study also showed that abnormalities within the SHOX gene cause a massive height reduction of 18.6 centimeters (7.3 inches) in men, but just 8.9 centimeters (3.5 inches) in women. Once again, this suggests that this gene has a much greater impact on body height in males than it does in females.

“This finding is consistent with the hypothesis that reduced SHOX expression in females results in a net difference in height between the sexes,” write the authors of the second study.

Looking at both studies together, the researchers say it’s now becoming clear that this gene on the sex chromosomes plays a role in regulating adult height. At the same time, though, they concede that SHOX may not be the defining gene when it comes to this aspect of sexual dimorphism, and write that they “cannot exclude the possibility that as-yet-unrecognized genes or RNAs on sex chromosomes may exert sex-biased effects on height.”

The study is published in the Journal of Human Genetics.