How heritable are human traits like personality, height, mental health, physical health, education, religiosity, and conservatism? (h^2 estimates)

Here’s my attempt to compile the heritabilities (in the narrow sense of h^2) for many different interesting human traits.

First, let’s look at estimated heritabilities from five categories: body, mental health, physical health, cognitive/mind-related traits, and personality (including the Big Five personality traits).

Genetic Heritability (narrow sense - h^2) of a wide variety of human traits, including physical health, mental health, body, personality, and mind related traits

You can find high-resolution versions of these charts here:

Note that here, we are looking at h^2, which represents the “narrow sense heritability”. It measures the proportion of phenotypic variance in a population that is attributable to additive genetic variance. This measure focuses specifically on the additive effects of alleles, excluding other genetic effects like dominance or epistasis. In particular,

h^2 = (additive genetic variance) / (total phenotypic variance).

All of the h^2 numbers in this article come from (or are derived from) papers (or from combining papers). In most cases, these h^2 numbers were calculated by comparing the similarity of traits between monozygotic / MZ (identical) and dizygotic / DZ (fraternal) twins to isolate the additive genetic component. The intuition for how such studies estimate heritability is that the more similar identical twins are in that trait relative to fraternal twins, the more heritable the trait generally is.

Note that h^2 is different than H^2 (broad sense heritability, sometimes written h_b^2 or h_{b}^2), which measures the proportion of phenotypic variance attributable to all genetic factors, including additive, dominance, and epistatic (gene-gene interaction). In particular,

H^2 = (total genetic variance including additive, dominance, and epistatic variances) / (total phenotypic variance).

H^2 will always be greater than or equal to h^2. The two numbers will be similar in cases where the additive genetic variance constitutes the majority of the total genetic variance.

For traits heavily influenced by dominance or gene-gene interactions, H^2 will be significantly larger than h^2. Examples include traits influenced by a few genes with strong dominance effects or complex traits with significant gene-gene interactions.

Note that h^2 values should be considered rough approximations only. Calculating them can be complex and estimates can vary for a variety of reasons, including:

Differing populations: sometimes h^2 will differ in different human populations due to differences in genetics or differences in environmental influences
Equivalent environment assumption: if identical twins and fraternal twins don’t “share their environment” to the same extent, that can lead to issues in calculation. If identical twins share more similar environments than fraternal twins, heritability may be overestimated.
Gene-environment correlations: if there is a correlation between genetics and the environment experienced by individuals, this can bias estimates.
Differences in the environment: heritability estimates are merely estimates of the percent of phenotypic variation that is accounted for by genetics in a particular environment. If the environment changes, this number can be expected to change. For instance, if everyone’s environment became more identical, heritability would go up because the environment then can’t account for as much variation.
Simplifying assumptions: additionally, sometimes additional assumptions are made when estimating heritabilities. For example, Falconer’s formula says that h^2 = 2 (r_MZ – r_DZ) where r_MZ is the correlation coefficient for monozygotic (identical) twins and r_DZ is the correlation coefficient for dizygotic (fraternal) twins. But Falconer’s formula makes some assumptions, for instance, that the correlation in traits between twins is not significantly influenced by shared environmental factors, that the effect of genes on the trait is independent of environmental factors, and that assortative mating doesn’t occur (i.e., parents of the twins are not more similar to each other in terms of the trait than would be expected by chance).

Heritability figures will sometimes change as the environment changes. For instance, in an extreme situation where every person has an identical environment, the only variation is genetic. Hence, the more constrained an environment is the greater the heritability.

A common misconception is that zero heritability would imply that genes are not involved. Suppose, though, that in a specific population, everyone has a gene causing trait X (which the environment then modifies). The heritability of X for that population will be found to be 0, even though the trait is caused by a gene!

Now, let’s look at the heritability of all traits in one bar chart:

And here is a list of heritabilities in table form:

Trait	Estimated Heritability (h² – narrow sense)

Body	average: 72%
Eye color	92%
Body Mass Index (BMI)	75%
Height	73%
Athletic ability	47%

Mental Health	average: 51%
Schizophrenia	77%
Bipolar disorder	76%
Eating Disorders	56%
Conduct disorder	49%
Alcoholism	49%
OCD	47%
Phobias	43%
Generalized Anxiety	32%
Depression	30%

Physical health	average: 47%
Cleft Lip	78%
Migraine	53%
IBS	49%
Heart disease	48%
Blood pressure	47%
Insomnia	39%
Dental Caries/Cavities	33%
Breast cancer	31%

Cognitive/Mind	average: 47%
IQ (adulthood)	74%
Conservatism	56%
Musical ability	48%
Education	41%
IQ (age 9)	41%
Religiosity	38%
Sexual orientation	28%

Personality	average: 44%
Openness	56%
Extraversion	55%
Neuroticism	50%
Conscientiousness	48%
Agreeableness	46%
Self-consciousness	38%
Impulsiveness	36%
Altruism	34%
Trust	30%