Ancestral reconstruction of κ-casein and the representation of pI, dN/dS ratio and the stomach pH values. Ancestral values are represented in grey. The ratio dN/dS was calculated only for species with a well-defined cDNA (this is not the case for guinea pig, cat, and dog). When the ratio dN/dS is undefined due to extremely small dS values we used the symbol "--". Despite the fact that the pH of other digestive compartments can show marked differences between mammals, we chose only to represent the stomach pH values, as this compartment is the main first barrier for milk proteins. A review of the pH values is reported in Table 5 of the following reference  (p366), we could not find well-defined values for chimp, horse, cow, and guinea pig.