Y n u and n are Y axis and X axis, respectively, and then we can draw three different curves, which are named as IE, IA, and EA curves of the protein sequence. The three different curves can give us some information about the protein sequence. According to the IE curve, we can compare the numbers of the amino acids belonging to the internal group and the external group at different positions. The IA curve can then be used to compare the numbers of the amino acids belonging to the internal group and the ambivalent group at different positions. Finally, the EA curve can compare the numbers of the amino acids of the external group and the ambivalent group at different positions. According to the above definitions of three different curves, we drew three curves of ND6 proteins for the eight species (Fig. 1 ). Fig. 1 shows that the amino acids of the internal group in ND6 protein sequences are more than the amino acids of the external group, and the amino acids of the ambivalent group are more than the amino acids of the external group. Furthermore, it is evident that G. seal and H. seal have similar curves, rat and mouse's curves are almost identical, and the three curves of human, gorilla, and chimpanzee are similar, but wallaroo's curve is different from curves of other species.