Sibudu Cave site plan (Villa et al. 2005) Archaeological sites in such landforms develop in unpredictable ways. At times they can be net depositional, at others, they can be net erosional. They are very prone to flushing out by running water, which creates temporal breaks of unpredictable magnitude, and they are easily and predictably susceptible to what’s called ‘reverse stratigraphy,’ where objects that find their way into low-lying areas can be buried by older sediments transported from upslope.

In this view it’s possible to see the steepness of the north-south slope (If you took this photo or know its ascription, please advise how I should best handle the credit).

Villa et al. (2005) publish a profile of the excavation’s north-wall (shown below), which illustrates nearly horizontal layers in the west-to-east direction at the surface. By presenting the site stratification using this profile the authors are [one hopes] inadvertently downplaying the potential for re-entrainment and secondary deposition across the excavation area. 

Excavation profile illustrating the north wall of squares B5 and B6 (Villa et al. 2005).

To illustrate the potential for downslope transport in the excavated area, I developed a generalized slope diagram from the site plan, seen below, which allows you to see the north-to-south slope perpendicular to the plane of the profile drawing. The slope is fairly steep, and it wouldn’t take much surface water or treadage to mobilize small particles on the surface. A downpour would no doubt create a torrent on a slope of this magnitude, capable of transporting sediments up to and probably exceeding small pebbles.

Schematic north-south slope of site sediments based on contours in the site plan above, showing the location of the profile in the excavation profile reproduced below.

     The excavators claim that the strata of preserved vegetation are the result of deliberate preparation of a comfortable working/sleeping surface. Moreover, they claim that the bed builders regularly burned old vegetation mats, and that in one case they selectively collected the leaves of one species because it conferred an insecticidal property to the area of the leaf mat. In support of these claims the authors employ just a single premise. And it all boils down to this statement: 

‘Many woody plants grew near Sibudu during the MSA; thus, single-taxon windborne leaf litter seems improbable.’ 

As far as I can tell this is the only reason they concluded that purposeful human/hominid behaviour is the explanation for such a deposit. But, why must we accept that only wind-borne leaves could have contributed to the deposits?  
     I’m mystified as to their reasoning with regard to the source of the vegetation mats. Given the likelihood that, in the MSA, dense vegetation grew everywhere in front of and above the cave (indeed, all but in the drier areas underneath the overhang, much as in the present day photo, above), let’s imagine instead a more likely scenario–leaf-fall. A plant grows, loses leaves, and those leaves come to rest beneath or very near to the stalk or trunk. It’s the origin of the term leaf litter. Makes sense, doesn’t it? We don’t need to construct an elaborate scenario whereby the palaeo-humans went about collecting leaves for bedding–they merely had to use what nature would in all likelihood have provided for them. Or, am I missing something?
     And what about the single species mat? No real mystery there. The species in question is Cryptocarya woodii. This is no bush, nor is it a shrub. It’s a hulking great tree! Moreover, it’s not a mostly leafless, splindly thing like the one in the photo above. It’s a tree that can grow to 20 m high, and from the look of the growth habit visible in the photo below, the tree is every bit as wide as it is high, and has an abundance of leaves. Hmmm.

Cryptocarya woodii grows from 5 to 10 m high, but it can grow to 20 m in favourable conditions (Photo credit).

Given the species in question, how unlikely is it [really] to imagine a 1 m by 2 m ‘carpet’ of leaves accumulating beneath a single individual of the species that would have dominated a 20-m diameter area? Not very, unless I miss my guess. And what about the mat remaining intact while natural processes buried it? Well, in a closed woodland, at the end of a valley, you might not expect too much in the way of air movement that could blow the leaves around once they’d fallen to the ground. Clearly the right circumstances prevailed to have aided preservation, unless we imagine purposeful burial of disused mattresses! What about the follow-on assertion that the vegetation mat was insecticidal? You tell me! Almost all plants produce substances that are toxic to other organisms. Think about it. Deadly nightshade. Oleander. Wormwood. Hemlock. I could go on. Cryptocarya woodii  happens to produce a substance that mosquitos avoid. Whoop-de-do. Given the improbability that the palaeo-humans made this bed of leaves, how likely is it that they chose the Cryptocarya woodii blanket over other accumulations at Sibudu so there wouldn’t be clouds of mosquitos buzzing around? I’ll leave that up to you to decide.

[I think the authors of ‘Man the Fat Hunter’ should have used a hyphen in the title, unless they wanted to imply that Homo erectus, as a species, was fat! Something tells me that’s not the case.] 

[If you find me remiss in not quibbling with the gender-exclusive language in the title, please understand that those of us old enough to remember Sputnik know that the title is an allusion to a pivotal conference in palaeoanthropology–‘Man the Hunter’–which took place in the 1960s, and set the terms for the archaeology of human evolution for a generation thereafter.] This is gonna be so. Much. Fun.