Humans and apes are genetically very similar.

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MAN'S closest living relatives are the great apes—the African chimpanzee and gorilla, and the Asian orangutan. Humans (Homo) are classified in the family Hominidae; chimpanzees (Pan), gorillas (Gorilla) and orangutans (Pongo) are classified in the family Pongidae. The gibbons, or lesser Asian apes (genera Hylobates and Symphalangus), are classified in the family Hylobatidae. All three families of humans and apes are included in the superfamily Hominoidea. Linnaeus recognised the basic morphological similarities between humans and apes by placing them together in the order primates (Anthropomorpha), although in separate genera. He did not use any category of classification intermediate between ‘genus’ and ‘order’. However, when the ‘family’ category was introduced, humans and apes were placed in separate families. The prevailing view of modern taxonomists has been expressed by Simpson1: “Homo is both anatomically and adaptively the most radically distinctive of all hominoids, divergent to a degree considered familial by all primatologists”. With the methods of classical mendelian genetics it is impossible to make genetic comparisons between species which cannot be hybridised, as the presence of genes is ascertained by studying segregation in the progenies of crosses between individuals exhibiting different traits. However, advances in molecular biology have made possible comparisons between DNA sequences or, more often, between proteins from different organisms. If the proteins are identical in amino acid sequence, the genes coding for them are assumed to be identical. (This is not always true owing to the redundancy of the genetic code, but DNA nucleotide differences which change the encoded protein have greater evolutionary consequences than those which do not.) Many proteins from different organisms can be readily compared by means of gel electrophoresis. Although not all amino acid differences are detected by this method, it provides reasonably satisfactory estimates of the relative degree of genetic differentiation between closely related species. King and Wilson2 studied electrophoretically 44 gene loci coding for proteins in humans and chimpanzees (Pan troglodytes), and found them to be about as similar as very closely related species of other organisms are to each other. We now report results confirming that finding and extend it to comparisons between humans and the other apes.