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The Howiesons Poort industry used to be seen as a distinct horizon marker that occurred at the same time in MIS 4 all over southern Africa. At Diepkloof the dates published by Zenobia Jacobs (science 322 (2008), 733–735) fell on a continuous unbroken line all through the 4 m of sediment. In their new determination Tribolo et al. were able to estimate systematic errors of up to 10 % in Jacobs’ work and then proceed to date the Early HP to nearly twice the former age. Their new dates form two distinct clusters at MIS 5c-d (105 ka) for Pre-SB to EHP and MIS 5a-b (80 ka) for IHP while more or less confirming Jacobs’ date for LHP at around 62 ka in MIS 4. Incidentally this clustering in two distinct events, which may be up to 10 ka long each but may just as well have lasted 100 a or less, is at variance with their own conclusion of HP having been a long lasting phenomenon of about 50 ka.
Their dates do however fit well with the detailed description of the sediment layers by Miller et al.. SB and EHP are found in a 130 cm thick anthropogenic layer of ash and bedding that may well have grown quickly. It is overlain by a thin (20 cm) sterile authigenic layer covering perhaps several tens of thousands of years and again overlain by 110 cm of anthropogenic material containing the IHP and LHP.
Another new article by Klein & Steele calls into question the second of Jacobs’ conclusions. In accordance with the well known Tasmania effect and e.g. Mackay (J.Arch.Sci. 38 (2011), 1430–40; list of 2011-06-17) she attributed the appearance and decline of SB and HP to rapid population expansions during wet and stable climate optima. Looking at a size decline of shells in middens due probably to intensive exploitation Klein & Steele deny any significant population rise before the LSA, but their data seem too coarse to me to be able to see the short term excursions postulated by Jacobs (Communicative & Integrative Biology 2 (2009), 191–193).
In all the Still Bay and Howiesons Poort phenomena now look even more complicated and multi-faceted than they already did before, with all that implies for the emergence of the human mind and modern behaviour.
Humans are much better at throwing things than any other ape. Anatomical considerations by Roach and Larson place that change towards the beginning of the genus Homo at around 2 Ma ago, about the same time other evidence places the beginning of hunting behaviour.
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