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Abstract The idea of heritability concerns whether the differences actually observed between individuals arose because they started life with different genotypes or were exposed to different environmental forces. Every characteristic is both hereditary and environmental since its expression can be changed by appropriate changes either in its heredity or in the environment under which that genotype develops. The degree of heritability may be defined as the fraction of the observed variance which was caused by differences in heredity. This fraction is a statistic describing a particular population. It can be made larger or smaller if either the numerator or the other ingredients in the denominator can be altered. Thus it may vary from population to population for the same characteristics and may vary from one characteristics to another even in the same population. All ways of estimating heritability rest on the degree to which animals with similar genotypes resemble each other more than less closely related animals do.
Jay L. Lush (Sun,) studied this question.