Similar to what was seen in α-LA, none of these changes were predominantly among the EAA (Figure 1; Supplemental Table S1). β-Casein has evolved rapidly, potentially giving rise to dramatic changes in AA frequencies. A considerable range of frequency of Trp was observed, extending from 0% in rodents to 5% in primates (Supplemental Table S1; http://dx.doi.org/10.3168/jds.2013-7317), because of the relatively sudden gain of this AA in the primate ancestor. Such an abrupt change may therefore have some consequences for nutrition.