A very important new paper deals with the problem of the taxonomic validity of various postulated species of hominins, i.e., of species of Hominidae related to humans, including our own genus, Homo, and its species, including Homo sapiens, the only extant hominin species.
Hominins have evolved from short, small-brained ancestors to tall, large-brained ones, and it is clear that humans of today are quite different from human-like creatures of millions of years ago. But, do these differences represent different lineages, or stages of a single evolving lineage?
The controversy between lumpers, who group different specimens into few species and splitters who name new species even on minute differences -considered of taxonomic significance, is nothing new, and the new paper supports an extreme "lumper" position, namely that all hominins represent a single evolving lineage, and hence its various "species" should not be acknowledged.
The authors test discover a clear temporal and geographical trend in the evolution of hominins, but they realize that the various specimens are not differentiated enough from each other to merit designation as distinct species. They could simply be stages of the evolution of a single lineage, snapshots separated in space and time of the evolution of a single species.
Of course this does not prove that hominins are a single species. But, it does show that statistically there does not exist enough evidence for postulating multiple different species; such species cannot be rejected, but the most parsimonious explanation at present is the single-lineage one.
HOMO - Journal of Comparative Human Biology
Volume 55, Issues 1-2 , 18 October 2004, Pages 21-37
Hominins are a single lineage: brain and body size variability does not reflect postulated taxonomic diversity of previous termhomininsnext term
M. Henneberg and C. de Miguel
Fossil previous termhomininnext term taxonomy is still debated, chiefly due to the fragmentary nature of fossils and the use of qualitative (subjective) morphological traits. A quantitative analysis of a complete database of previous termhomininnext term cranial capacities (CC, n=207) and body weight estimates (Wt, n=285), covering a period from 5.1 ma (millions of years) to 10 ka (thousands of years) shows no discontinuities through time or geographic latitude. Distributions of residuals of CC and Wt around regressions on date and latitude are continuous and do not differ significantly from normal. Thus, with respect to these characteristics, all previous termhomininsnext term appear to be a single gradually evolving lineage.