What does it mean to say that the heritability of a trait is 70 percent?

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Heritability refers to the proportion of variability in a trait within a population that can be attributed to genetic factors. When we say that the heritability of a trait is 70 percent, we mean that 70 percent of the variability in that trait within a population is accounted for by genetic variation. This does not mean that 70 percent of a person's expression of that trait is due to heredity or that 30 percent is due to environmental factors, as the expression of any trait is always the result of both genetic and environmental factors. Similarly, while the correlation between identical twins is often used as a way to estimate heritability, this is not the definition of heritability itself, and the correlation between identical twins for a trait with a heritability of 70 percent could be higher or lower than +0.70.

What Does It Mean to Say That the Heritability of a Trait