Heritability

Heritability of Intelligence

Heritability is perhaps the most debated and studied concept in the field of intelligence research. It refers to the proportion of the difference in IQ scores between people that can be attributed to genetic factors versus environmental factors.

It is important to note that heritability describes populations, not individuals. A heritability of 50% does not mean that 50% of your intelligence comes from your genes; it means that 50% of the variation in intelligence across a group of people is due to genetic differences.

The “Nature vs. Nurture” Split

Modern consensus in behavioral genetics suggests that intelligence is highly heritable, but the degree changes throughout life.

• Childhood (20-40%): In young children, the home environment (parents, books, nutrition) plays a massive role.
• Adulthood (60-80%): As we age, our genetic predispositions assert themselves more strongly. By adulthood, genes are the single biggest predictor of IQ.

The Wilson Effect

This increase in heritability with age is known as the Wilson Effect. It suggests that as we grow up and gain independence, we select environments that match our genetic propensities. A child with high genetic potential for reading will choose to go to the library, thus reinforcing their verbal IQ. In this way, our genes drive us to create our own environments.

Polygenic Nature

Intelligence is polygenic, meaning it is influenced by thousands of tiny genetic variations, not just a single “smart gene.” Recent Genome-Wide Association Studies (GWAS) have identified hundreds of specific gene variants linked to educational attainment and cognitive function, though each individual variant has a tiny effect.

Conclusion

While environment matters—especially in cases of extreme deprivation—the scientific literature overwhelmingly supports the conclusion that general intelligence (g) has a strong biological and genetic basis.