(a) Correlation between ERV count and body mass for the number of ERV integrations acquired over the last 10 my.

<p>(b) Correlation between mean age of all ERV integrations and body mass from the genomes of 38 mammals. Body mass is log-transformed, and the mean ages are calculated correcting for the substitution rate. We have not taken into account the effect of body size on substitution rate in calculating the ages.