Pearson correlation of substitution rates between neighboring mammalian genes and evidence of selective pressures. 20 mammalian species and 26 species pairs are shown. In striking contrast to the fungi, every mammalian comparison gives a highly significant correlation between rates of neighboring genes (column 7). (Right) Similar types of genes have unusually low or unusually high silent substitution rates across the mammals, suggesting universal selection pressures. Genes in the categories RNA binding, regulation of transcription – DNA dependent, nucleus, or transcriptional activator activity (blue text) have unusually low silent substitution rates in virtually every mammalian species pair, as marked by ovals. Gene associated with receptor activity have unusually high silent substitution rates (red text) in most mammalian species pairs.