A general problem in biology is how to incorporate information about evolutionary history and adaptation into taxonomy. The problem is exemplified in attempts to define our own genus, Homo . Here conventional criteria for allocating fossil species to Homo are reviewed and are found to be either inappropriate or inoperable. We present a revised definition, based on verifiable criteria, for Homo and conclude that two species, Homo habilis and Homo rudolfensis , do not belong in the genus. The earliest taxon to satisfy the criteria is Homo ergaster , or early African Homo erectus , which currently appears in the fossil record at about 1.9 million years ago.