Functional and morphological stasis during molecular evolution

The evolutionary distance between two sets of proteins was estimated using the techniques of Miyata and Yasunaga (1980) and Kimura (1980). Human beta 2-microglobulin was compared with the homologous murine molecule, while human and equine alpha-globin were similarly treated. It was found that a large amount of molecular evolution has occurred in beta 2-microglobulin since its divergence from the common ancestor of mice and humans. Kimura's estimate of evolutionary distance, K, is 0.353, while those of Miyata and Yasunaga are KS = 0.708 and KA = 0.171. The respective values for human and equine alpha-globin are 0.152, 0.293, and 0.084. In spite of this molecular evolution, it is shown that murine beta 2-microglobulin can effect the expression of HLA class I antigens on the surface of human-mouse hybrid cells and that the tertiary structures of human and equine deoxyhemoglobin are nearly identical. These observations are discussed in the light of Kimura's theory of neutral allelic drift.