ABSTRACT
Heritability often summarizes the extent to which a particular population has responded to a regimen of being bred selectively on the basis of the expression of some trait, as is done for milk production in cattle and egg production in poultry. Heritability values vary on a continuum between zero and plus one. If the distribution of trait expression among progeny remains the same no matter how their parents might be selected, then heritability has zero value. If parental selection does make a difference, heritability exceeds zero, its exact value reflecting the parent-offspring correlation. Heritability estimates for repeated measurements of behavioral characters have been found to increase, decrease, and fluctuate randomly as a function of repeated testing. Heritability provides no information about norm of reaction. Since the characterization of genotype-environment interaction can only be ad hoc and the number of possible interactions is effectively unlimited, no wonder the search for general laws of behavior has been so unfruitful.
