Ghosts of extinct apes: genomic insights into African hominid evolution.

African apes are humans' closest evolutionary relatives, yet their fossil record is almost nonexistent. Genomics shows that, despite the fact that African ape lineages originated 6–12 million years ago (Ma), the diversity within the living species is very young (<1 Ma), similar in age to the diversity of recent hominin species, such as modern humans and Neanderthals. The hominin fossil record shows deeper and greater diversity compared with that of the African apes, suggesting that, across hominine evolution, they must have experienced a high rate of extinction, with repeated replacements and dispersals. Recent genomic studies also suggest that African apes had higher levels of diversification in earlier periods, and it is likely that a high rate of extinction and replacement occurred. This raises questions about the last common ancestor, the conditions under which apes evolved, and the adaptive and dispersive nature of the current species. We are accustomed to regular announcements of new hominin fossils. There are now some 6000 hominin fossils, and up to 31 species. However, where are the announcements of African ape fossils? The answer is that there are almost none. Our knowledge of African ape evolution is based entirely on genomic analyses, which show that extant diversity is very young. This contrasts with the extensive and deep diversity of hominins known from fossils. Does this difference point to low and late diversification of ape lineages, or high rates of extinction? The comparative evolutionary dynamics of African hominids are central to interpreting living ape adaptations, as well as understanding the patterns of hominin evolution and the nature of the last common ancestor. [ABSTRACT FROM AUTHOR]