How tall was your great-grandmother?

Why your grandmother looks even shorter beside you

The marks on the frame are height at 18. From about 30 people start to shrink: by 70, on average by about 3 cm for men and 5 cm for women, and by 80 by 5 and 8 cm (a study that followed 2,084 people in Baltimore for years). So the gap you see standing next to an 80-year-old grandmother is bigger than the gap between your marks. And to be fair, measure at the same time of day: in the evening you are almost 2 cm shorter than in the morning.

If height is inherited, why did we grow?

It is true that height is largely inherited. In twin studies in rich countries about 80% of the variation in height between people is down to genes; for men, in eight countries, between 87 and 93%, for women between 68 and 84% in most countries and up to 89–93% in four of them. But that says why, within one generation, one person is taller than another. It does not say why a whole generation is taller than the one before: in 100 years a people’s genes change far too little to explain 11 centimetres. Perkins and colleagues put it plainly: there is “no inherent contradiction” between high heritability and a rapid rise.

What changed, then?

Childhood. A child who eats enough and is not always ill spends its energy on growing. In 12 rich countries after 1950, deaths of children between one month and one year, a measure of childhood disease and poor nutrition, statistically explain 62% of the differences in adult height; “disease, not income” was the brake, write Bozzoli, Deaton and Quintana-Domeque. In Portugal, the average of men’s and women’s self-reported height rose from 164 cm (born 1950–55) to 168 cm (born 1976–80); over the same time those deaths fell from 61 to 11 per 1,000 births.

Same genes, another country: the two Koreas

North and South Korea share one people: the peninsula was split in 1945, and the two states have existed since 1948. In 1997, preschool children in South Korea were on average 6–7 cm taller than those in the North; in 2002, about 8 cm.

Why are the Dutch so tall? Here researchers disagree

In the mid-18th century, by military records, Dutch soldiers averaged about 165 cm; Dutch men born in 1996, 182.5 cm. Milk, prosperity and a society with little inequality: that is the usual explanation. Gert Stulp and colleagues showed in 2015, on 94,516 people, that taller men had more children and that natural selection may help explain it. Other biologists (Tarka and colleagues, 2015) calculated that this effect is “minuscule”. And Pavel Grasgruber, who finds that average height in European countries tracks protein from milk, pork and fish, wrote in 2022 that 18-year-old Montenegrins (182.9 cm) outstrip the Dutch (182.4 cm), and thinks their case is more likely genetic. That too is a hypothesis, not a fact.

Why did the rise stop?

Not only in Romania. Americans were long among the tallest people in the world, but their rise slowed around mid-century; US men born in 1946 were 176.9 cm, those born in 1996, 177.1 cm. Nobody knows for sure where a people’s ceiling lies. In Romania the generations after 1980 have stayed about level, and the 95% interval is too wide to say whether they fell or not.

Sources and method

Each mark on the frame is the mean height at 18 of people born in Romania in that year, as estimated by the NCD Risk Factor Collaboration from a model that pools 1,472 studies, with more than 18.6 million people measured, in 200 countries. The smudge around the mark is the model’s 95% credible interval: given their data and model, the true mean almost certainly lies inside it.

For Romania the model has only three sources: a heart study in Bucharest in 1986–87 of people aged 35–64 (so born roughly between 1922 and 1952), one in Dolj (2009–11) and one in Timiș (2014). So Romanian measurements cover only the generations born roughly 1922–1952 and a few hundred young people born around 1988–1996; the other years are estimated from the trend and from neighbouring countries, and for those born before 1922 there is no Romanian measurement at all. The model also corrects for a generation measuring shorter as it ages: a little over 0.2 cm for men and 0.3 cm for women per decade.

The children in “The class” come from a second model by the same team (The Lancet, 2020), for the year 2019. The two series do not join into one: one is height at 18 by year of birth, the other height at a given age in a given year.

The data give means and intervals, not how widely people are spread around the mean. So the page never tells you what percentage were shorter than you, only how many centimetres you stand from the mean.

• NCD Risk Factor Collaboration (2016). A century of trends in adult human height. eLife 5:e13410. doi.org/10.7554/eLife.13410
• NCD-RisC: country data, adult height by year of birth, 1896–1996 ncdrisc.org/data-downloads-height.html
• NCD Risk Factor Collaboration (2020). Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories. The Lancet 396:1511–1524. doi.org/10.1016/S0140-6736(20)31859-6
• Pop RM, Tenenboum A, Pop M (2021). Secular Trends in Height, Body Mass and Mean Menarche Age in Romanian Children and Adolescents, 1936–2016. IJERPH 18:490. doi.org/10.3390/ijerph18020490
• Perkins JM, Subramanian SV, Davey Smith G, Özaltin E (2016). Adult height, nutrition, and population health. Nutrition Reviews 74:149–165. doi.org/10.1093/nutrit/nuv105
• Silventoinen K et al. (2003). Heritability of adult body height: a comparative study of twin cohorts in eight countries. Twin Research 6:399–408. doi.org/10.1375/136905203770326402
• Bozzoli C, Deaton A, Quintana-Domeque C (2009). Adult height and childhood disease. Demography 46:647–669. doi.org/10.1353/dem.0.0079
• Schwekendiek D, Pak S (2009). Recent growth of children in the two Koreas: a meta-analysis. Economics & Human Biology 7:109–112. doi.org/10.1016/j.ehb.2009.01.001
• Stulp G, Barrett L, Tropf FC, Mills M (2015). Does natural selection favour taller stature among the tallest people on earth? Proc R Soc B 282:20150211. doi.org/10.1098/rspb.2015.0211
• Tarka M et al. (2015). Did natural selection make the Dutch taller? A cautionary note on the importance of quantification. Evolution 69:3204–3206. doi.org/10.1111/evo.12803
• Grasgruber P et al. (2022). Mapping the Mountains of Giants. Biology 11:786. doi.org/10.3390/biology11050786
• Grasgruber P, Cacek J, Kalina T, Sebera M (2014). The role of nutrition and genetics as key determinants of the positive height trend. Economics & Human Biology 15:81–100. doi.org/10.1016/j.ehb.2014.07.002
• Komlos J, Lauderdale BE (2007). The mysterious trend in American heights in the 20th century. Annals of Human Biology 34:206–215. doi.org/10.1080/03014460601116803
• Sorkin JD, Muller DC, Andres R (1999). Longitudinal change in height of men and women. American Journal of Epidemiology 150:969–977. doi.org/10.1093/oxfordjournals.aje.a010106

Also about bodies, families and inheritance, on this site

• Why You're Taller in the Morning Than at Night
• How many ancestors did you have in the year 1000?
• Genes Take the Lead at Ten