The genetic similarities among all people and between humans and other animals are important and interesting, but that other 1 percent of our genes—less than 1 percent actually—are the genes that make each of us look and act differently from other people. Those genes underlie differences in people’s personalities.
When we say that heritability is the proportion of phenotypic variance that is attributable to genotypic variance, we’re saying that it’s the proportion of the total variability that we observe in a characteristic that’s due to variability in genes.
For instance, out of all of the variability that exists across people in their degrees of stubbornness, what proportion of that variability is due to genetic influences?
If the heritability of a characteristic, such as stubbornness, is zero, then none of the variability in that trait is due to genetic factors. On the other hand, if the heritability is 1, then all of the variability we see in stubbornness is genetic. If heritability is 0.2–0, then 20 percent of all the variability among people in stubbornness is genetic.
Heritability is not a constant value across all groups, situations, and times. Remember that heritability is the proportion of observed variability that is due to genetic variability. If everybody grew up in exactly the same environment, heritability will always be very high because none of the variability in their personality would be due to differences in their environment.
If the heritability of a characteristic, such as stubbornness, is zero, then none of the variability in that trait is due to genetic factors. On the other hand, if the heritability is 1, then all of the variability we see in stubbornness is genetic. If heritability is 0.2–0, then 20 percent of all the variability among people in stubbornness is genetic.
Heritability is not a constant value across all groups, situations, and times. Remember that heritability is the proportion of observed variability that is due to genetic variability. If everybody grew up in exactly the same environment, heritability will always be very high because none of the variability in their personality would be due to differences in their environment.
