Rate of evolution of conserved kiwi coding sequences and gene expression levels. The three categories of expression level are based on kiwi as well as chicken embryonic expression data (blue) or based on kiwi embryonic expression data only (red). A. Mean divergence (substitutions per site) at nonsynonymous sites in kiwi genes from different expression levels. B. Average divergence at synonymous positions. Error bars show the standard error of the mean estimates. The number of genes used are given in parentheses.