Hominin taxic diversity: Fact or fantasy?

In this review of the evidence for and against taxic diversity within the hominin clade, we begin by looking at the logic and the history of simple "ladder-like" interpretations of the hominin fossil record. We then look at the hominin fossil record in a series of time intervals and use current published evidence about the first and last appearance dates of each taxon to decide whether a species or specimens should be included in one, or more, of the intervals. Within each time interval, we consider the strength of the evidence that more than one hominin species is sampled. Decisions about whether taxonomic diversity exists depend on what alpha taxonomic hypotheses are used and although we use a relatively speciose interpretation of the hominin fossil record, we also explore what impact more inclusive interpretations of alpha taxonomy would have on assessments of hominin taxic diversity. With the exception of the oldest (7-5 Ma) all of the other time intervals have in our judgment at least one well-supported example of taxic diversity and several have multiple examples. In summary, not all new hominin taxa are created equally, but while taxic diversity may not be as prevalent as some have claimed, it is a feature of the hominin clade from 4 Ma until c.40 ka years ago.