The LRT to test whether differences in population size can explain the differences in v in human and macaque was constructed as follows. The null model assumes v h = v c and v m = 0.732v h (see Results). The alternative model also assumes v h = v c but leaves v m as a free parameter to be estimated from the data. Because the models are nested, a x 2 df~1 distribution is used for significance testing. This test was applied separately to each gene.