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 β 2 ‐microglobulin was compared with the homologous murine molecule, while human and equine α‐globin were similarly treated. It was found that a large amount of molecular evolution has occurred in β 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 K S = 0.708 and K A = 0.171. The respective values for human and equine α‐globin are 0.152, 0.293, and 0.084. In spite of this molecular evolution, it is shown that murine β 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.