“Comparing Nariokotome only to humans and only to relative scales, while instructive, involves us in an endless series of “if thens” (e.g., Smith, 1993; S.L. Smith, 2004). Only by adding a comparison to our closest relatives (Table 10.1) do we begin to generate a choice between alternatives: if Nariokotome is an odd fit to human growth standards, is he a better fit to something else?”
– M.C. Dean and B.H. Smith, “Growth and Development of the Nariokotome Youth, KNM-WT 15000.” In The First Humans – Origin and Early Evolution of the Genus Homo, F.E. Grine, J.G. Fleagle and R.E. Leakey (eds.). Springer, 2009.
I’ve struggled with this, because on the one hand, they’re right, it’s nice to have some additional context for understanding an aberrant observation (in this case, the relative development of Nariokotome). But at the same time, it sets up a largely false dichotomy of ape-like vs. human-like – what if the fossil is not really like either? Plus it doesn’t really obviate raising “an endless series of ‘if-thens.'” If anything it may raise more, just check out Anton and Leigh’s (2003) study of H. erectus facial growth (in http://bit.ly/FQibQo).