Is intelligence in your genes or in how you grew up? Decades of twin and adoption studies give a nuanced answer: both matter, and the mix changes over a lifetime.
What heritability means
When researchers say IQ is "50 percent heritable", they mean that in a given population, about half of the differences between people can be statistically linked to genetic differences. It does not mean half of your own intelligence comes from your parents. Heritability describes groups, not individuals.
It rises with age
In young children, shared environment (home, family, school) explains a large share of differences, and estimates of heritability are lower, often around 20 to 40 percent. By adulthood, estimates are much higher, commonly 60 to 80 percent. One idea is that as we grow up we choose and shape our own environments in ways that fit our natural tendencies.
Why genes are not destiny
- Hundreds or thousands of genes each contribute a tiny amount. There is no "intelligence gene".
- Genes work through environments: a child with great potential but no access to books or good sleep will not show it.
- Average scores have changed across generations far faster than genes can, which shows environment matters.
What you can control
Nutrition, sleep, education, reading, curiosity, safe surroundings and a habit of practising hard things are all within reach. They do not rewrite your genes, but they decide how fully you use what you have.
For children, the best support is simple: read together, ask "why?" questions, play puzzle and strategy games, and protect sleep. Curious how your child reasons? Try the Kids IQ Test.