There is no reason at all to suppose that Howieson’s Poort (or the earlier Still Bay) was made by people who embarked from southern Africa on an “out of Africa exodus.” The southern African sites are important enough for what they tell us about cultural variability; I don’t see the need to exaggerate their significance to the global story.
In many ways, the paper relies on similar methods as found in the 2007 paper by Michael Waters and Thomas Stafford, “Redefining the age of Clovis.” In that paper, the authors applied a statistical model to new and existing radiocarbon dates, which allowed them to conclude that the age interval represented by Clovis sites is relatively narrow – probably as little as 200 years.
Comparison with climatic records shows that these bursts of innovative behavior cannot be explained by environmental factors alone. The review of why these two MSA industries are important, I think, overstates the issues to a considerable extent.
A modification to standard irradiation practices is suggested as a remedy to this problem, whereby laboratory regeneration doses are administered in 10 Gy pulses, with the aliquot then being heated to 240 °C following each pulse.
Empirical measurements of 12 sedimentary samples support the theoretical findings, with significant differences in dose response being observed between single-irradiation and pulsed-irradiation OSL regeneration data.
Anytime we have to deal with dates from different methods or different laboratories, there is the potential that some will be systematically different. Or are they essential evidence of a more extensive time range, during which an industry was relatively rare?
Hamilton and Buchanan (2007) found a spatial gradient in Clovis radiocarbon dates, suggesting that they represented a wave of advance from north to south.
Modelling of quartz luminescence suggests that the usual practice of administering laboratory doses at room temperature, and in single exposures, may lead to both equivalent-dose overestimation and increased levels of scatter in individual age estimates for samples with palaeodoses greater than 40 Gy.
In the model, this effect is due to the large differences between laboratory and natural dose rates.That deals with ambiguity about earlier dates and different methods quite simply: The authors did not rely on dates from other labs and sources.They do present a figure that puts other labs’ dates in the context of their own results (they are consistent with the paper’s conclusions), but these do not form the main interpretive context.Howieson’s Poort and Still Bay cultures are a start in this process.The short duration of the two industries is a very important fact.The figure also shows paleoclimate evidence from ice cores; the Howieson’s Poort appears to correspond to a long warming period, but it spans the range of climate from cold to warm.