That’s the least I can say after looking at the matter with some attention: that the claims made by a recent paper are not sufficiently justified to say the least.
Katerina Harvati et al., The Later Stone Age Calvaria from Iwo Eleru, Nigeria: Morphology and Chronology. PLoS ONE 2011. Open access.
They tell us of a recent pair of skulls from SW Nigeria. They were discovered in 1965 and at least one of them belongs to a whole skeleton, including a critical piece: the mandible. Sadly this paper totally ignores anything but the calvaria (the top of the skull). They have been dated by uranium series to c. 12-6 Ka ago.
Sloppiness seems too common in this paper: not just the two skulls and skeletons are not properly shown in full but, in fig. 1, they claim to be showing both calvaria, they only show one from four angles:
Then we are thrown into PC analysis, which seems to be their main working tool:
Of course PC analysis is limited in its ability to discern and can only provide a very rough view. In any case, here we have PC2/CV2 occupied by intra-modern variability, while only PC1/CV1 show anything that resembles modern-archaic differences: a totally unilinear analysis in the end.
As we know, sample size matters; but instead of balancing it by reducing the number of modern samples (grey dots), the authors have totally ignored this matter.
So we get an (unclearly legitimate) linear archaic-modern horizontal dimension in which some individuals typically considered Homo sapiens of archaic traits (magenta and black triangles) tend to occupy intermediate positions between the erectus-neanderthal-heidelbergensis conglomerate (left) and the modern human oversized sample (right). Iwo Eleru (IE, black cross) is within this “ambiguous” group and resembles other archaic H. sapiens from the Middle Paleolithic (magenta triangles), as well as similarly aged Upper Cave 101, from North China.
UC 101 (UC1, pictured left) is a great counter-example because with Jebel Irhoud or the Palestinian skulls, there’s always someone claiming archaic admixture, typically with Neanderthals. But Upper Cave individuals are invariably described as modern in spite of their low vaults, so similar to those of “archaic” Homo sp. A good reason is that they have clear, unmistakably modern, chins.
To me, the calvarium looks very similar in shape to Iwo Eleru. To be safe I compared them both using fig. 4-A as tool:
|Inner drawing: Iwo Eleru, outer drawing: modern mean|
The comparison may be a bit imperfect but it is clear that the shape of both calvaria, of similar age, one from West Africa and the other from East Asia, are very much alike – and both are somewhat different from the modern mean.
I think therefore that at least serious doubt must be casted on the conclusions that some want to extract from this paper: that there was some sort of archaic hominin in West Africa until recently. Nothing in this data suggests this, instead it does suggest that a better methodology is much needed.