6 - The Muddle in the Middle

Summary

Once Louis Leakey and his colleagues had described Homo habilis in 1964 the search for his Holy Grail of the “earliest Homo” was on, and the field was wide open for other entrants that had very little in common with Homo sapiens, the species by which our genus is defined. Genera are hopefully monophyletic collections of species descended from the same common ancestor; but there are no formal rules governing how inclusive they can be, so you could in theory create a monophyletic genus by including every primate on the planet. By unwritten convention, however, zoological genera are in effect the largest readily (I almost wrote “intuitively”) recognizable unit, species being basically variations on the theme established by the genus. All species of the genus Felis are identifiably cats, and all Rattus are visibly rats. By this rule-of-thumb, as Bernard Wood and Mark Collard pointed out over two decades ago, the genus Homo should be confined to species that have significant resemblances to Homo sapiens. Just being related to the Homo clade, at some remove, is simply not enough.