One of the most spectacular advances in the last 10 years in our knowledge of human genetic diversity has been the discovery of the abnormal hemoglobin genes. In this short space of time the distributions of these genes in the world's populations have become one of the best known genetic systems for any animal species. In fact, the great mass of data makes it difficult to summarize our knowledge of these genes in a single paper, and the heterogeneity of these data emphasizes once again the great genetic variability which exists among the populations of the human species. Although we know more about the hemoglobins, this is but one of the many genetic systems which the increasing precision of biochemical techniques has brought to our attention. The haptoglobins, transferrins, and others yet to be discovered will increase our knowledge of human genetic diversity still further. Another significant advance in recent years, which preceded the discovery of the hemoglobins, was the development of the modern genetic theory of evolution. This synthesis was a theoretical advance as much as a factual one and was developed primarily from data on animals other than man. It has been applied to some extent to the blood group genes, but because we know so much more about the factors of evolution as regards the abnormal hemoglobin genes, this system is the first one for the human species for which we can discuss the factors of evolution and their interrelationships. Since, in addition, we also know the environmental circumstances which determine the direction of natural selection, the principal factor of evolution, we can effectively evaluate the role of culture as one of the environmental determinants of human evolution at the hemoglobin locus. While the populational aspects of the abnormal hemoglobin genes have been of great interest to anthropologists and geneticists, biochemists have also made significant advances in the chemical structure of hemoglobin so that hemoglobin is one of the best known complex proteins. The chemical structure of this molecule has been directly related to gene action as no other has. We now know that genes are composed of DNA, which, through RNA, directs the manufacture of proteins or polypeptide chains, but for the hemoglobin molecule we know the exact changes in the molecule which are associated with the gene differences. (The biochemical advances are discussed by Ingram, 1963.) As the specific changes which genes produce have been discovered, it has been realized that similar phenotypic characteristics, whether based on observation with the naked eye or biochemical tests, can result from very different genetic structures. For example, one can talk about the gene for albinism and even calculate the mutation rate to this gene, but we now realize that literally dozens of different genetic changes may result in phenotypically similar albinism. This specificity of genes also has implications for measuring gene flow between populations. Many of the characteristics which have been used to claim genetic relationships between populations may well be due to very different genes. The abnormal hemoglobins, as the first system where we know the specific chemical changes involved, have made it possible to discuss the basic concepts of mutation, gene flow, and natural selection in a much more realistic way. In 1953 after the development of paper electrophoresis made mass surveys for the abnormal hemoglobins quite easy, an international committee was convened to