Height Is Genetic — Does Effort Even Matter?

"Drink lots of milk to grow tall", "Play basketball before your growth plates close", "Sleep more to get taller" — advice everyone has heard. But scientifically, the evidence that height is almost entirely determined by genetics is overwhelming.

Identical Twin Studies — The Strongest Evidence

The most powerful way to measure genetic influence is to compare identical twins raised in different environments.

The Minnesota Study of Twins Reared Apart, running since 1979 for decades, tracked hundreds of identical twin pairs separated at birth and adopted into different families.

Results were striking. One twin raised in a wealthy family, the other in a poor family — adult height difference averaged only 1-2cm. Identical twins raised apart were more similar in height than fraternal twins raised together.

The Netherlands — World's Tallest Nation

Dutch men average about 182.5cm, ranking #1 globally. Just 150 years ago, the Dutch were among the shorter Europeans. What happened?

Natural selection hypothesis: A 2015 London School of Hygiene study found taller Dutch men had more children. Analyzing ~94,500 people across 7 generations, taller men had higher reproductive success. Natural selection concentrated "tall genes."

Nutrition improvement helped too. But other European nations (France, Italy) that improved nutrition similarly didn't grow as tall as the Dutch. Nutrition is the prerequisite; genes determine actual height.

GWAS Research — Thousands of Height Genes Found

A 2022 Nature mega-GWAS analyzed 5.4 million people's genetic data and identified 12,111 genetic variants (SNPs) affecting height. These variants alone could predict 40% of individual height variation.

Note: 40% doesn't mean "only 40% is genetic." It means currently identified variants explain 40%. Including undiscovered variants, the scientific consensus is 80-90%+ is genetic.

Heritability Numbers Summary

Developed countries: 80-90%. With adequate nutrition, most height variation between individuals is explained by genetics.

Developing countries: 60-70%. Malnutrition limits growth, so environmental factors weigh more.

The key insight: When nutrition is sufficient, genetics determines almost everything. When nutrition is lacking, genetic potential simply can't be expressed — the genes themselves don't change.

North Korea vs South Korea — Same Genes, Different Nutrition

The Korean peninsula is a natural experiment. North and South Koreans are genetically nearly identical, but nutrition diverged dramatically after division.

South Korean men in their 20s average ~173.5cm; North Korean ~165cm — over 8cm difference. This looks like evidence for "environment matters."

But studies of defector families show children born and raised in South Korea reach near-normal South Korean heights. Same genes + adequate nutrition = normal height. Environment is the "key" that unlocks genetic potential, not the determinant of height itself.

Japan's Height Change — Limits of Nutrition

Japanese male average height went from 160cm (1950s) to 171cm (2000s) — an 11cm increase from post-war nutrition improvement.

But since the 2000s, height has plateaued. Nutrition didn't worsen, yet growth stopped. This is evidence of reaching the genetic ceiling. Beyond sufficient nutrition, genes don't permit more.

Summary (Not Conclusion)

• Developed countries (adequate nutrition): 80-90% genetic, 10-20% environment

• Developing countries (poor nutrition): 60-70% genetic, 30-40% environment

• Extreme malnutrition: Genetic potential cannot be expressed at all

"Height is genetic" isn't wrong. More precisely: "Genetics sets the upper limit; nutrition determines whether you reach it."

Drinking milk doesn't make you taller — not drinking milk (poor nutrition) prevents you from reaching the height you could have been.