Amino acids displaying considerable enrichment at various points in evolution are Thr (in rabbit); Ala, Val, and Pro (in rat); Glu (in the rodent ancestor); and Gly (in dog). Those notably depleted are Ala (in horse); Val and Glu (in primates); Pro (in cat and opossum); Thr and Gly (in guinea pig); and Trp (chimp).