In mammals, bitter taste is mediated by TAS2Rs, which belong to the large family of seven transmembrane G protein-coupled receptors. Since TAS2Rs are directly involved in the interaction between mammals and their dietary sources, it is likely that these genes evolved to reflect species' specific diets during mammalian evolution. We have investigated intra- and inter-species differences in the function of TAS2Rs of primates in protein and behavioral levels. The results suggest the common mechanism of the diversification of sensory receptors dependent on the species specific environments.<br>