Original sentence: A trait can have a heritability of 1.0 in a population at some time, yet this could be completely altered in the future by a simple environmental change.But the misunderstanding about the relationship between heritability and phenotypic plasticity is not simply the result of an ignorance of genetics on the part of psychologists and electronic engineers.Furthermore the assumption that gene-environment interaction can be presented as a simple dichotomy assumes that these factors act independently, but environments affect genes and genes affect environments.Heritability is not a measure of the contributions of genes and environments to any individual phenotype, a fruitless enterprise as both are subsumed within the processes of development.If this were not the case, ‘inborn errors of metabolism’ would be forever incurable, which is patently untrue.It arises from the entire system of analysis of causes through linear models, embodied in the analysis of variance and covariance and in path analysis.Lewontin’s classic article on the analysis of variance in human behavioural genetics warrants continued attention for perhaps the worst of them: the article makes several correct observations that continue to remain under-appreciated in some research and much discussion about the causal role of genes in human outcomes.Often measures of heritability are erroneously presented as a simple gene/environment dichotomy.Part of this confusion is due to a misunderstanding of heritability, heritability in a technical context measures the contribution of genes to the variance of a traight about the mean of a group.The fallacy is that a knowledge of the heritability of some trait in a population provides an index of the efficacy of environmental or clinical intervention in  altering the trait either in individuals or in the population as a  whole.The lucidity of Lewontin’s arguments has historically proven no match for the allure of overly simple characterizations of outcomes as being x% due to genes and (1 - x)% not due to genes.This fallacy, sometimes propagated even by geneticists, who should know better, arises from the confusion between the technical meaning of heritablility and the everyday meaning of the word