Men are taller than women on average by about five inches, but that gap has puzzled researchers for decades. It is not some universal rule of nature, and in many animal species, females outsize males.
A new breakthrough study offers a clear piece of the puzzle, and it all comes down to genetics.
Men owe part of their height advantage to a gene called SHOX. This gene is found on both the X and Y chromosomes, and its placement and activity work differently depending on sex. The research team analyzed genetic data from nearly a million people and found that men receive a double boost in SHOX activity compared to women.
This discovery sheds light on almost a quarter of the average height gap between men and women.
Rare Chromosome Patterns Reveal Insights
Scientists looked at rare genetic conditions in which people carry extra or missing sex chromosomes. These unusual cases offered a natural experiment. They found that an extra Y chromosome adds more height than an extra X. That surprising twist confirms that the SHOX gene works harder when linked to a Y chromosome.
The SHOX gene sits near the tip of the sex chromosomes. In women, one of their two X chromosomes shuts down most of its genes to prevent overload. However, SHOX sits so close to the tip that it stays partially active.
Even so, that partial activity does not match the full effect seen in men, whose X and Y both stay active.
Researchers calculated that this single gene explains about 25% of the height gap between men and women. The remaining difference comes from other genetic factors and the influence of male sex hormones during growth. Testosterone, for example, boosts bone growth and helps men reach taller adult heights.
Evidence From Rare Genetic Cases
Men with atypical chromosomes provided the crucial data points. People with conditions like XYY tend to be taller than average, while those with Turner syndrome, who have a single X chromosome, tend to be shorter. These patterns match perfectly with the SHOX hypothesis, reinforcing the idea that the gene is a major driver of height.
The study, published in the Proceedings of the National Academy of Sciences, highlights how big data and genetic sleuthing can reveal everyday traits we take for granted. The team pulled genetic records from biobanks in Britain and the United States, combing through nearly a million profiles to find just over 1,200 individuals with rare sex chromosome variations.
While those factors do play roles, this genetic insight shows a direct link at the molecular level. It is a reminder that traits like height are the result of many small influences working together over time.
This discovery also opens the door to deeper research. Doctors may be able to better understand growth disorders by studying how SHOX functions. Therapies could target this pathway in children with unusually short stature. Knowing exactly how this gene works gives medicine a valuable tool.
