Psychology › Personality & intelligence
Heritability: nature and nurture
Galton's phrase, 1874· Concept
Well replicatedStrong, repeated evidence.
Heritability is the share of differences between people in a trait that traces to differences in their genes, within a given population.
See it on the Psychology map →What it says
Francis Galton popularized the pairing 'nature and nurture' in 1874. Heritability is a population statistic, not a statement about one person: 50 percent means half the variation across a group links to genetic differences. A 2015 review of 50 years of twin studies, covering about 14.5 million twin pairs, found an average near 49 percent across traits. High heritability does not mean fixed: height is about 80 percent heritable, yet average height rose sharply with better nutrition.
Why it matters
It reframed nature versus nurture as nature and nurture. Nearly every psychological trait is partly heritable, yet environment still matters, and the number varies by setting.
Think of it like
Like asking how much of the rent spread across a city's buildings comes from location versus management: it describes the market, not any single building.
The evidence
Twin, adoption and family studies, now joined by DNA studies of hundreds of thousands of people. Galton also coined 'eugenics,' a dark misuse of hereditary thinking that later fueled forced sterilization.
Open questions
'Missing heritability': DNA studies explain far less variation than twin studies do. Whether twin estimates run high or the genetics is too diffuse to capture yet is debated.
Inside this (2)
Connections (3)
▸Temperament in infants is partly explained by Heritability: nature and nurtureWell replicated
The connection
Twin studies show temperament traits like activity level, shyness and fussiness are moderately heritable, with estimates often between about 20 and 60 percent. The rest reflects environment, including prenatal conditions, parenting and chance. Shared home environment matters more for some infant traits, like positive mood, than it does later in life.
Who showed it and when
Twin studies of infants and toddlers since the 1980s, including work by H. Hill Goldsmith and Jerome Kagan's research on shy, inhibited children.
The evidence
Identical twin babies resemble each other more than fraternal twins on observed and parent-rated temperament, in several countries.
Open questions
Few specific genes have been identified. Some children seem especially sensitive to environment, for good or ill, a 'differential susceptibility' idea still being tested.
▸The Flynn effect: rising IQ scores complicates simple readings of Heritability: nature and nurtureWell replicated
The connection
IQ is substantially heritable within a generation, yet average scores rose about 15 points in a few generations, far too fast for genetic change. This shows heritability says nothing about what causes average differences across time or between groups; environments can still shift a whole population.
Who showed it and when
Flynn and economist William Dickens proposed a resolution in 2001: small advantages draw people into richer environments, multiplying their effects.
The evidence
Gains appeared within decades in many countries' conscript records, too fast for genes; recent within-family declines also point to environment.
Open questions
What exactly caused the gains is still debated, as is what the effect implies for contested arguments about group differences in average scores.
▸Twin and adoption studies estimate Heritability: nature and nurtureWell replicated
The connection
Twin studies turn comparisons into heritability estimates. A rough rule: double the gap between how alike identical twins are and how alike fraternal twins are. If identical twins correlate 0.8 on a trait and fraternal twins 0.5, heritability is about 0.6. Adoption studies offer a cross-check.
Who showed it and when
Galton suggested the twin method in 1875; large twin registries followed from the mid-20th century in Scandinavia, Australia and the US.
The evidence
A 2015 meta-analysis of 2,748 twin publications found average heritability near 49 percent; DNA-based methods confirm genes matter but give lower numbers.
Open questions
Whether identical twins' more similar treatment inflates estimates, and why DNA studies capture less than twin studies, the 'missing heritability' problem.