Heritability in retrospect.

The origin of the word heritability remains unknown. Its usage has evolved through three stages, becoming more restrictive in its meaning along the way. In the initial stage, 1832 and possibly earlier, heritability was used to denote the hereditary transmission of characteristics or material things, simply having the capability (legally or biologically) of being inherited. The second stage, beginning around the turn of this century, followed Johannsen's classical definition of nongenetic or environmental fluctuations distinct from genotypic differences, and usage closely approximated "broad sense heritability" and Johannsen's Erblichkeit. Finally, in 1936, we come to the modern day usage of narrow sense heritability, the ratio of additive genetic variance to the total phenotypic variance within a population, and credit Dr. J.L. Lush with its origin.