We've just had a paper published in Methods in Ecology and Evolution on "Simultaneously estimating evolutionary history and repeated traits phylogenetic signal". This work, lead by Bram Vrancken, Philippe Lemey and Marc Suchard, estimates *phylogenetic signal* in a fully Bayesian fashion, integrating over uncertainty in evolutionary history. This method provides an estimate of the extent to which variance of a continuous trait (like viral load) can be explained by evolutionary relatedness and thus gives an estimate of the trait's heritability.

Of particular interest to me, is that this method gives a heritability estimate of influenza antigenic phenotype of ~0.73, which it quite high and supports a strong genetic basis to antigenic phenotype. Here, total variance in a phenotype trait stems from a combination of variance due to genotype and variance due to the environment $V_P = V_G + V_E$, so that heritability is measured as the proportion of the total variance explained by genotype $H2 = V_G / V_P$. In the case of influenza antigenic phenotype we expect noise in the hemagglutination inhibition (HI) assay to contribute to total variance, so *H*^{2} = ~0.73 should represent a lower bound to actual heritability.