Heritability: What it does and doesn’t mean

When psychologists talk about personality traits, they often talk about the “heritability” of those traits. But what does this mean?

The term heritability can be confusing to the uninitiated. When we say that height is about 90 percent heritable, you might expect that this would mean that a person’s height is determined 90 percent by genetics and 10 percent by the environment.

But that’s not what heritability means. In fact, the term heritability can never apply to an individual at all. Heritability is about how a trait manifests itself within a population. For any given trait in a population, heritability is the degree to which variability between individuals is due to genetics.

What this means is that a trait such as hair color can be genetically inherited without being heritable. For example, the Inuit—the igloo-dwelling indigenous tribes of Northern Canada—have black hair. So even though hair color is entirely hereditary, the “heritability” of the trait among the Inuit is 0 since there’s no genetic variation within the population[1].

So when we say that height is 90 percent heritable, that doesn’t mean you can look at a shorter man and say, “This man’s short stature is 90 percent due to genetic factors.” You don’t know; it could be that the man is short because of disease or poor nutrition as a child. What it means is that in the population you’re considering, 90 percent of the differences in height among individuals is due to genetics.

How do scientists quantify the relative influence of genes and environment on a given trait? Heritability can be assessed by comparing individuals with varying degrees of genetic relatedness. For instance, if you take monozygotic twins (who are genetically identical) and determine how similar they are on a trait like conscientiousness, and compare that to the degree of similarity among dizygotic twins (who, like non-twin siblings, share 50 percent of their genes), you can estimate how much of the variability for that trait is due to genetics and how much is due to the environment.

Psychologists have found that extraversion is around 54 percent heritable[2], and that the degree to which you like jazz music is about 40 percent heritable. But saying the trait is heritable doesn’t mean it’s set it stone and can’t be changed. Nor does it mean, for instance, there’s a specific gene for liking jazz. After all, there are literally billions of people who have never even heard of jazz. What is heritable, though, are the elements of personality and intelligence that influence enjoyment of certain kinds of art.

Traits and Their Estimated Heritability[2]

Trait                                            Heritability

Personality

Extraversion                                   .54

Agreeableness                               .42

Conscientiousness                         .49

Neuroticism                                    .48

Openness                                       .57
Intelligence                                      .88
Psychiatric illness

Schizophrenia                                .80

Major depression                           .37

Panic disorder                             .30–.40

Generalized anxiety disorder         .30

Phobias                                       .20–.40

Alcoholism                                   .50–.60

Antisocial behavior                         .41
Political orientation

Under age 20                                 .00

Over age 20                                .45–.65
Religiousness                               .30–.45

Specific religion                           near zero

?References

1. Indiana.edu (2016). “Heritability.” www.indiana.edu/~p1013447/dictionary/herit.htm
2. Bouchard, T. (2004). Genetic influence on human psychological traits: A survey. Current Directions in Psychological Science, 13, 148-151.