Men are taller than women on average in every country measured, by roughly 7%.1Our World in Data. Human Height The biggest reason is timing: boys keep growing for longer before their bones lock in their final height. But hormones are not the whole story. Genes on the sex chromosomes and the conditions a child grows up in also shift the difference.
Boys Grow For About Two Years Longer
On average, girls’ teenage growth spurt starts around age 10 and boys’ around age 12.2PubMed. The timing and duration of adolescent growth The fastest growth comes about two years after the spurt begins, near 12 for girls and 14 for boys.3PubMed. The timing and duration of adolescent growth Growth in height ends around 17 and a half in girls and about 19 in boys.4PubMed. The timing and duration of adolescent growth Most children land within about a year either side of these ages.5PubMed. The timing and duration of adolescent growth
The spurt itself lasts about the same time in both sexes.6PubMed. The timing and duration of adolescent growth So the adult gap comes far more from boys’ later start than from a bigger spurt.7PubMed. The adolescent growth spurt of boys and girls of the Harpenden growth study
Before puberty, children grow steadily, several centimeters each year. A boy still growing that way while girls his age begin their spurt keeps adding height. He then starts his own spurt from a taller base, so he finishes taller. That is also why 11 or 12 year old girls are often taller than the boys in the same class. Those girls are briefly ahead, and it says nothing about how tall either will end up. Boys usually catch up and pass them over the next two or three years.
For the same reason, one measurement is a poor guide to final height. A child who is the smallest in the class at 12 may simply be a late starter whose growth has years left to run. A child who is tallest at 12 may be an early starter who will stop sooner. Doctors judge growth by following a child’s own curve over time, not by comparing a single number with classmates.
Estrogen Closes the Growth Plates in Both Sexes
Long bones grow at growth plates, soft zones of cartilage near each end of the bone. During childhood the cartilage cells keep dividing, and the bone beneath turns the newest cartilage into hard bone, so the bone lengthens a little at a time.
Rising estrogen late in puberty makes the growth plates close, which stops growth.8PubMed Central. The role of estrogen receptor-α and its activation function-1 for growth plate closure in female mice Estrogen speeds up the plates’ natural aging until their cells stop dividing, and then the cartilage is quickly replaced by bone.9PubMed Central. Effects of estrogen on growth plate senescence and epiphyseal fusion A thin scar-like line is left where the plate was. This happens in the long bones of the legs and arms, which is why adult height cannot increase afterward even though other parts of the body keep changing.
Estrogen does this in young men too, made in their bodies from testosterone.10PubMed Central. Effects of estrogen on growth plate senescence and epiphyseal fusion Girls, whose estrogen rises earlier, have their plates close sooner. The same hormone also contributes to the spurt itself, so the hormone that speeds growth early on is the one that ends it.
Rare cases show how much power estrogen has. Men who cannot make or respond to estrogen never fully close their growth plates and keep growing into adulthood, becoming very tall.11PubMed. The influence of estrogen on growth Some of these men grow tall even without normal growth hormone, because they get extra years of growth.12PubMed. Tall stature without growth hormone: four male patients with aromatase deficiency Testosterone-type hormones, meanwhile, can drive the growth spurt without a rise in growth hormone.13PubMed. Androgen-stimulated pubertal growth: the effects of testosterone and dihydrotestosterone on growth hormone and insulin-like growth factor-I in the treatment of short stature and delayed puberty Testosterone fuels the spurt, but much of its role in ending growth runs through estrogen.
A bone age X-ray of the hand lets doctors see how open the growth plates still are. Open plates mean more growth is possible. Once they fuse, no treatment adds height to the bones, which is why worries about a child’s growth are best raised before the mid teens.
Genes on the X and Y Chromosomes Also Matter
The SHOX gene, found on both the X and Y chromosomes, helps the limbs grow longer.14PubMed Central. Complex Phenotypes: Mechanisms Underlying Variation in Human Stature Losing a copy is linked to short stature, as in Turner syndrome, where an X chromosome is missing.15PubMed Central. Complex Phenotypes: Mechanisms Underlying Variation in Human Stature Extra copies are linked to tall height, as in men with an extra X.16PubMed Central. Complex Phenotypes: Mechanisms Underlying Variation in Human Stature Men with an extra Y chromosome also grow taller, without their body proportions changing.17PubMed. Effects of the Y chromosome on quantitative growth: an anthropometric study of 47,XYY males An extra Y adds more height than an extra X, separate from male hormones.18PubMed Central. X and Y gene dosage effects are primary contributors to human sexual dimorphism: The case of height
SHOX is less active in women’s growth cartilage than in men’s,19bioRxiv. Pseudoautosomal gene SHOX exhibits sex-biased random monoallelic expression and contributes to sex difference in height and the Y copy seems to stay more active than a woman’s second X copy. The effect is small, but it builds across all of childhood, giving a small height difference that becomes clear by adulthood.20PubMed Central. SHOX and sex difference in height: a hypothesis
People with XY chromosomes who are raised on female hormones, or whose bodies ignore male hormones, still reach heights near the male average.21PubMed Central. Transgender Girls Grow Tall: Adult Height Is Unaffected by GnRH Analogue and Estradiol Treatment So genes, not just hormones, set part of the gap.
None of this means every man is taller than every woman. Thousands of other genes shape height in both sexes, and ordinary height genes vary far more between people than between sexes. A tall woman may simply carry more height-raising variants than a short man, along with having grown up in good conditions.
How Food and Hardship Change the Gap
Before birth and through childhood, boys’ growth suffers more under stress than girls’.22American Journal of Physical Anthropology. Sex differences in environmental sensitivity during growth and development A growing baby needs a steady supply of nutrients from the mother, and when that supply is poor the baby must choose between growing and surviving. In a hard pregnancy, girls in the womb tend to slow growth to survive while boys keep growing,23Elsevier / Placenta. Review: Sex and the human placenta: mediating differential strategies of fetal growth and survival which leaves boys more exposed if supplies run short later on.
The effects show up in adults. In poor rural Mali, women came closer to healthy height standards than men did.24PubMed. Nutritional status of adults in rural Mali Stressful national conditions cut male height more than female.25PubMed Central. People Are Taller in Countries With Better Environmental Conditions When children are underfed, boys lose more of their potential, so the average difference between men and women shrinks.
Good conditions work in the opposite direction. Across countries, as living standards rose, men gained about 4 cm while women gained 1.7 cm.26the Guardian. Men have grown twice as much as women over past century, study shows In the UK, about one in four women born in 1905 was taller than the average man, but only one in eight born in 1958.27the Guardian. Men have grown twice as much as women over past century, study shows Worldwide, though, the gap barely moved over a century, from about 11 cm to 12 cm.28eLife. A century of trends in adult human height
Faster, longer male growth needs more food and energy, so the gap tracks a society’s nutrition. Culture matters too: in some ancient farming groups girls got less food, which made the gap larger.29bioRxiv. Socio-cultural practices affect sexual dimorphism in stature in Early Neolithic Europe
For parents, steady nutrition, sleep and treating illness support full growth for any child. No food makes a child grow past their genetic range, and big gains mostly come where children were underfed.
How Big the Gap Is Around the World
With men taller by roughly 7% on average, a population where the average woman is 162 cm would have an average man around 175 cm.
The gap is smallest across Sub-Saharan Africa.30Our World in Data. Human Height Researchers do not agree on a single cause, and the reasons likely include nutrition, health and population history.
About a century ago the gap was slightly bigger in poorly fed countries, but now it is similar across tall and short nations.31eLife. A century of trends in adult human height Tall-man countries tend to have tall women too.32eLife. A century of trends in adult human height
Why Evolution Kept Men Taller
The classic idea is that bigger men won more contests for partners.33prosocial.world. What’s True About the Evolution of Men’s Greater Average Height In other primates, size gaps go with males fighting over mates.34PubMed. Sexual size dimorphism, canine dimorphism, and male-male competition in primates: where do humans fit in? But the human gap could also come from competition for resources, group conflict and female choice.35PubMed. Sexual size dimorphism, canine dimorphism, and male-male competition in primates: where do humans fit in? These pressures do not exclude each other, and they could all have pushed male height up together. Because they acted over very long periods and left no direct record, they are hard to test separately, so the evidence supports a mix of causes rather than one proven answer.
Mate preferences may play a part. In one modern population, taller men and shorter women had more children.36PubMed Central. Women’s height, reproductive success and the evolution of sexual dimorphism in modern humans Women often prefer taller partners, while men pay more attention to cues of fertility.37PubMed Central. Women’s height, reproductive success and the evolution of sexual dimorphism in modern humans
Growth also competes with reproduction. The body splits energy between growing, reproducing and staying alive.38PubMed. The ecology and evolutionary endocrinology of reproduction in the human female In Finnish women, earlier first births went with slightly shorter adult height.39Evolution and Human Behavior. A tradeoff between reproduction and growth in contemporary Finnish women One idea is that stopping growth earlier may let girls reach fertility sooner.