For centuries, the average height difference between men and women has been noticeable—men generally stand about five inches taller. While environment and nutrition contribute to this variation, science has long suspected that genetics plays a major role.
Now, thanks to one of the largest studies of its kind, researchers have identified a gene that helps explain part of the reason why men tend to be taller.
Height and the Role of the SHOX Gene
At the center of this new discovery is a gene called SHOX. This gene is located on both the X and Y sex chromosomes. Men carry one X and one Y chromosome, while women carry two Xs. What makes SHOX intriguing is how it behaves differently depending on which chromosome it’s on.
Researchers have known that SHOX plays a role in growth, but what they didn’t fully understand was how it might contribute to sex-based height differences. In this study, a team analyzed the genetic and health data of nearly one million people from biobanks in both the US and the UK to find clues.
Why an Extra Y Makes a Difference
Some rare genetic conditions result in individuals having an unusual number of sex chromosomes—such as an extra X or Y, or even a missing one. These unique cases helped researchers dig deeper. By comparing height in these individuals, they discovered that having an extra Y chromosome tends to increase height more than having an extra X chromosome.
This key finding suggests that the Y chromosome’s version of SHOX provides a stronger growth signal than the X. It’s not that the gene is entirely inactive in women; rather, because of a natural silencing mechanism that happens in one of the X chromosomes, the total dose of active SHOX is lower in women.
What Makes SHOX Special?
– Located near the tip of the X and Y chromosomes
– Escapes full silencing on the X chromosome
– Fully active on both X and Y in men
– Slightly reduced expression in women
This difference in dosage affects growth patterns and accounts for nearly 25% of the average height gap between men and women.
Other Factors That Influence Male Height
While the SHOX gene explains a notable portion of the difference, it’s not the full story. Hormonal influences—particularly male sex hormones—also play a significant role in promoting bone growth and length during adolescence. Additionally, other genetic factors contribute to height variation, though most are less pronounced in effect than SHOX.
Matthew Oetjens, a senior researcher involved in the study from Geisinger College of Health Sciences, pointed out that the position of SHOX near the chromosome tip is what allows it to escape full gene silencing in women—but not completely. This subtle distinction helps explain why men, with a fully active X and Y version, end up with a stronger growth boost.
Scientific Significance and Future Research
Eric Schadt, a geneticist from Mount Sinai School of Medicine, praised the study as an excellent use of population-scale biobanks. Although the increase attributed to SHOX may seem modest, accounting for about a quarter of the male-female height difference is still a significant finding. It’s a step forward in untangling the genetic complexity behind height variation.
The research also highlights the value of studying rare chromosomal patterns to understand broader biological traits. By learning how even a single gene behaves differently in men, scientists can better understand growth disorders and height-related conditions in both sexes.
One Piece of a Bigger Puzzle
The newly discovered link between the SHOX gene and male height gives scientists a sharper picture of how sex-based biological differences take shape. While SHOX is not the sole factor determining why men are typically taller, it plays a measurable and meaningful part in that outcome.
As genetic research continues to evolve, further insights may emerge to explain the rest of the height gap. For now, though, this study adds a valuable clue—one rooted in both biology and large-scale data—that helps explain a trait many have noticed but few fully understood until now.
