On average, human males tend to be about 5 inches (13 centimeters) taller than females. But why?
In short, we’re not sure. Even though this sex-linked height difference exists across the world, we still lack a full scientific understanding of why. But we do have a few clues from sex-linked genes and hormones that are helping to unravel this mystery.
Height is a complex trait influenced by many factors. One of these is genetics: Genes on both sex-linked and regular chromosomes help determine height. Every baby receives two sets of chromosomes: 23 from their mother and 23 from their father. Two of these chromosomes are sex chromosomes: Females tend to be XX and males are usually XY. Parents often contribute genes consistent with their own features, so usually taller parents will have taller kids than shorter parents do.
Studies of identical twins have found that height is about 80% heritable, meaning about 80% of the differences in height can be attributed to genetics.
But disentangling which genes contribute to height is complicated. “Height is a famously polygenic trait,” Alexander Berry, a bioinformatics scientist at Geisinger College of Health Sciences in Pennsylvania, told Live Science. This means that many genes influence it. Height can vary wildly based on the thousands of genes affecting it throughout the genome. “Genome-wide association studies that look at height find hits all over the genome,” Berry said.
One 2022 paper published in the journal Nature found 12,111 places in the genome where a single nucleotide — the G, A, T, or C in a DNA sequence — varies and is significantly associated with height.
Related: What determines a person’s height?
One of the best-studied genes connected with height is called SHOX, which is on both the X and Y chromosomes. SHOX is estimated to account for about 25% of the 5-inch-average disparity between males and females, Berry said. He added that gene variants in which SHOX loses its function on the X or the Y chromosome can lead to significantly reduced height. For example, the genetic disorder Léri-Weill dyschondrosteosis, which is caused by a mutated SHOX gene, affects bone growth and results in short stature.
Another place to investigate height disparities is in people with sex chromosome aneuploidy, or an atypical number of chromosomes, such as XXX or XXY. In a paper published in May 2025 in the journal PNAS, Berry and his team studied 928,605 people using data from three biobanks. Of this group, 1,225 people had sex chromosome aneuploidy. In these people, the researchers studied how the dosage — or number — of genes affects these sex chromosomes. In other words, how did more or fewer specific genes on these extra or missing Xs and Ys affect height?
The findings shed some light on how SHOX affects height in the average male and female. The team found that more Y chromosomes impacted height more than more X chromosomes did. In general, those with extra Ys tended to be taller than those with extra Xs. This is in part because those with XX chromosomes have one inactive X, meaning it doesn’t transcribe all the same genes, including SHOX. But someone with XY chromosomes has two sets of transcribing SHOX genes. For the average male and female, this finding supports that SHOX expression occurs at a higher rate in those with XY chromosomes than in those with XX.
But Berry cautioned that this finding doesn’t mean that the Y chromosome itself is responsible for this disparity.
“Our data doesn’t show that at all,” he said. SHOX occurs on both the X and Y chromosomes, so its impact on height isn’t unique to males. However, Berry said there could be Y chromosome-specific codings that impact hormones, like testosterone, which, in turn, can influence vertical growth. Testosterone is a hormone that both male and female sex organs produce, though males naturally make more of it. An androgen, testosterone is responsible for development of typically male characteristics like a deeper voice and more body hair.
“It’s likely that other genes on the Y chromosome influence hormone production, directly or indirectly,” he added. However, “the relationship between hormones and height is complicated.”
Related: Why do women tend to outlive men?
Other hormones contribute to growth, as well. Human growth hormone comes from the pituitary gland, promoting growth in children. Insulin-like growth factor 1 (IGF-1) mediates the effects of human growth hormone, with both peaking in puberty.
But in the story of hormones and height, “estrogen is a star,” Holly Dunsworth, an anthropology professor at the University of Rhode Island, told Live Science. Produced in both male and females during puberty, estrogen “is a major driver of long bone growth,” she said.
When it comes to bone growth, estrogen works in two phases. The first phase involves driving height. During the second phase, eventually there’s so much estrogen that the bones ossify, or fuse, Dunsworth said. Once estrogen production peaks in adolescents, their bones ossify. Estrogen production peaks sooner in females compared to males, who continue growing.
Dunsworth authored a 2020 paper published in the journal Evolutionary Anthropology exploring estrogen’s role in the height difference between males and females. Crucially, this hypothesis asserts that estrogen may partially explain the gulf in growth, as opposed to evolutionary speculation that males, as the supposedly more aggressive sex, simply evolved to be taller.
That said, a person’s sex isn’t the only factor that influences height; of course, some females are taller than males.
Beyond genetics and hormones, environment plays a significant role, too. Since height is 80% heritable, 20% is attributed to environmental factors, such as nutrition and climate. This confluence of drivers has made it difficult for researchers to definitively answer why men tend to be taller than women. But Berry thinks that another factor — gene expression — could be the next key to this mystery.
“I think we might find, with some larger gene expression studies, that height variation even among people with the same chromosomes varies because of gene expression.”
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