On the Number of Ancestral Human Species

Abstract For the clade containing humans and other bipedal apes (or ‘hominins’), species diversity and the tempo and mode of macroevolution remain major controversies. The present contribution considers these issues within a broad framework provided by living Catarrhines and employing molecular clocks for species branching times. The fossil record is shown to likely dramatically under sample species diversity for the hominin clade while at the same time substantially underestimating species longevity. Finally, the tempo of speciation is found to be much shorter in hominins than typically seen in Catarrhines suggesting the human clade may be characterised by a large number of rapidly evolving and relatively short‐lived species. Key Concepts: The clade containing humans (Tribe Hominini: vernacular ‘hominins’) possesses a large and diverse fossil record. All hominins except one ( Homo sapiens ) are now extinct, a paradox when compared to most primate groups. A proper understanding of hominin macroevolution requires a stable taxonomic framework founded in a reliable estimate of taxonomically relevant diversity. Hominin systematics is polarised into phenetic and cladistic schools of thought, each recognising starkly different levels of taxic diversity. Central to the historical practice of systematics has been the comparative method wherein evolutionary insights are provided by phylogenetic context. Hominins belong to the Parvorder Catarrhini, making Old World monkeys and apes phylogenetically appropriate analogues for testing scenarios about diversity and macroevolution. Molecular data for living and increasingly extinct primate species may be employed to test the question of diversity and to examine broad macroevolutionary trends. Molecular datasets avoid many of the biases and major gaps in the fossil record as well as providing an independent dataset to test existing scenarios. Primates are a charismatic mammal with an abundance of genetic data available for testing hominin macroevolution. Comparative investigations employing Catarrhine molecular data offer the potential to resolve conflicting hominin systematic and macroevolutionary hypotheses.