What does narrow sense heritability measure?

Narrow sense heritability specifically measures the proportion of phenotypic variance in a trait that can be attributed to the additive genetic variance among individuals within a population. This means it focuses on how genetic differences contribute to variation in traits. By assessing narrow sense heritability, researchers can evaluate the extent to which specific genetic factors influence a trait, indicating how likely it is that those traits will be passed down to offspring.

The emphasis on additive genetic variance is crucial, as it captures the cumulative effect of different alleles contributing to the expression of the trait. This understanding is essential in evolutionary biology and animal breeding because it helps predict how traits may respond to selection over generations.

In contrast, total genetic variance encompasses both additive and non-additive (dominance and epistatic) genetic contributions, while environmental influences pertain to factors outside of genetics. The focus on behavioral traits alone is also too restrictive, as narrow sense heritability can apply to a wide range of traits, not just those related to behavior.