Why Men Are Usually Taller Than Women

Gene Activity on the X and Y Chromosomes Influences Height

XY becomes taller than XX: Researchers have discovered that a specific gene on the X and Y chromosomes plays an important role in our height. According to the study, this gene is more active on the male Y chromosome than on the second X chromosome in women. This gives men additional height. However, height is also influenced by other factors, including hormones and chromosome number. The method could also be used in the future to study other gender differences.

On average, women are 14 centimeters shorter than men. photo:pixabay

Although men and women have essentially the same body structure, they differ in numerous biological characteristics, such as height. On average, women worldwide are almost 14 centimeters shorter than men. However, the genetic mechanisms underlying this sexual dimorphism in human height have only been partially researched so far. This is made more difficult by the fact that height depends not only on a single gene, but on the activity of hundreds of genes.

Researchers have long suspected one of these height-regulating genes: the SHOX gene. This gene is located on the sex chromosomes in our genome and is present on both the X and Y chromosomes. What's unusual about it is that, normally, women have genes on one of their two X chromosomes silenced, but this is not the case with the SHOX gene. According to analyses, the activity of this gene on the second X chromosome (Xi) is only slightly reduced. In men, the SHOX genes are also active on both sex chromosomes, the X and Y chromosomes. However, the extent to which this is affected is unclear.

Influence of Sex Chromosomes

Researchers led by Alexander Berry from the Geisinger College of Health Sciences in Pennsylvania have now investigated the influence of the SHOX gene on human height depending on gender and activity. They used a computer model to compare the height and genetic data of 928,605 adults.

The test subjects were predominantly people who conformed to the gender norm – women with two X chromosomes and men with one X and one Y chromosome. The team also examined 1,225 intersex individuals with an extra or missing sex chromosome. These individuals had the chromosome set X, XXY, XYY, or XXX. Statistically, such an abnormal chromosome set occurs in one in 450 people; in the biobanks used for the study, it was one in 758.

Height distribution by sex chromosome complement across cohorts. Mean heights of each sex chromosome complement are shown and indicated with dotted vertical lines. Analyses of 45,X height were not performed for the All of Us cohort because data cannot be reported for groups containing fewer than 20 individuals. Source: X and Y gene dosage effects are primary contributors to human sexual dimorphism: The case of height / PNAS / May 19, 2025

Y contributes more than Xi

The analysis showed that height increases depending on the chromosome count in the following order: X, XX, XXX, XY, XXY, and XYY. Accordingly, it is not only women who are shorter than men. Within the female sex, there is also a sequence in which height increases with increasing chromosome number. The situation is similar for men: If they have more chromosomes, they are, on average, taller.

The researchers conclude, firstly, that a Y chromosome with its SHOX gene contributes more to a person's height than a second X chromosome with its suppressed SHOX gene (Xi). Accordingly, the SHOX gene on the Y chromosome is more active than its counterpart on the Xi chromosome. This difference in activity contributes to the height differences between the sexes.

However, only about 23 percent of the observed height difference of 14 centimeters between XX women and XY men is due to this difference in gene activity on the sex chromosomes. This corresponds to approximately three centimeters. "The Y chromosome contributes an additional 3.1 centimeters to an adult's height compared to the Xi chromosome," the researchers say.

Hormones and chromosome number also play a crucial role

The number of sex chromosomes, and thus the number of SHOX gene copies, also plays a role in sexual dimorphism. Men and women with one extra X chromosome (XXY or XXX) are each a good five centimeters taller than the average XY man or XX woman. Men with an extra Y chromosome (XYY) are even more than eight centimeters taller than XY men.

However, the team also concludes from the data that hormonal differences between the sexes and chromosome sets play an even greater role in the height of men and women. In particular, male sex hormones, which are only produced in the presence of a Y chromosome, lead to increased height. They are responsible for the other almost eleven of the 14 centimeters difference in height between XX and XY, as the team explains.

It's all in the sum.

These influences of the sex chromosomes and their SHOX gene not only explain sexual dimorphism in human height, they can also explain why certain population groups are taller than others, as the team demonstrated using additional patient cohorts.

The various influencing factors add up: "For example, the height difference between XX individuals and XYY individuals can be estimated by adding the effects of male sex hormones, the difference in gene activity between the Y and Xi chromosomes, and an additional Y chromosome," write Berry and his colleagues, arriving at 11 plus 3 plus 8 equals 22 centimeters.

An explanation for other gender differences, too?

The method used in the study could also be applied in the future to decipher the biological mechanisms behind other gender dimorphisms in humans. For example, women have a greater risk of developing an autoimmune disease, while men are more often on the autism spectrum. Berry and his colleagues' analytical technique could use health data from individuals with different chromosome sets to determine the genetic influence of sex chromosomes on these health traits as well. (Proceedings of the National Academy of Sciences, 2025; doi: 10.1073/pnas.2503039122)

Source: Proceedings of the National Academy of Sciences (PNAS)