# From heritability to probability

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DOI: 10.1007/s10539-008-9129-7

- Cite this article as:
- Tal, O. Biol Philos (2009) 24: 81. doi:10.1007/s10539-008-9129-7

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## Abstract

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.