Can a heritability value tell us something about the weight of genetic versus environmental causes that have acted in the development of a particular individual? Two possible questions arise. Q1: what portion of the phenotype of X is due to its genes and what portion to its environment? Q2: what portion of X’s phenotypic deviation from the mean is a result of its genetic deviation and what portion a result of its environmental deviation? An answer to Q1 provides the full (...) information about X’s development, while an answer to Q2 leaves out a large portion unexplained—that portion which corresponds to the phenotypic mean. Q1 is unanswerable, but I show it is nevertheless legitimate under certain quantitative genetics models. With regard to Q2, opinions in the philosophical and biological literature differ as to its legitimacy. I argue that not only is it legitimate, but in particular, under a few simplifying assumptions, it allows for a quantitative probabilistic answer: for normally distributed quantitative traits with no G-E correlation or statistical G × E interaction, we can assess the probability that X’s genes had a greater effect than its environment on its deviation from the mean population value. This probability is expressed as a function the heritability and the individual’s phenotypic value; we can also provide a quantitative probabilistic answer to Q2 for an arbitrary individual where the probability is a function only of heritability. (shrink)

Despite the long history of scientific, philosophical, and political debate around heritability studies, certain fundamental conceptual issues have not been recognized or well appreciated. The starting point is that heritability does not measure the degree of influence that genes have on a trait or provide a reliable basis for choosing which traits to investigate further with molecular genetic research. The short argument on this point revolves around two issues: the disconnect between analyzing measurements of a trait and exposing the measurable (...) genetic and environmental factors underlying the trait’s development; and the possibility of heterogeneity in these underlying factors, that is, different factors may lead to the same trait value. The idea of underlying heterogeneity is elaborated through schematic diagrams and distinguished from other senses of heterogeneity. Five conceptually distinct approaches for addressing underlying heterogeneity are identified, corresponding to distinct ways of managing the reciprocal relationship between the degree of knowledge of the dynamics through which the trait develops and the actions that can be reliably be based on what is known . This framework, which extends the interventionist notion of causality, allows the scope and limitations of heritability studies to be clarified in greater detail. It can also inform critical appreciation of newer methods of analysis of genetic and environmental factors. The issues discussed in this article do not centre on empirical data or technical detail and should be accessible to non-specialists as well as challenging active researchers. (shrink)

In this book, Neven Sesardic defends the view that it is both possible and useful to measure the separate contributions of heredity and environment to the explanation of human psychological differences. He critically examines the view - very widely accepted by scientists, social scientists and philosophers of science - that heritability estimates have no causal implications and are devoid of any interest. In a series of clearly written chapters he introduces the reader to the problems and subjects the arguments to (...) close philosophical scrutiny. His conclusion is that anti-heritability arguments are based on conceptual confusions and misunderstandings of behavioural genetics. His book is a fresh and compelling intervention in a very contentious debate. (shrink)