This paper focusses on two of the ten botanical samples taken from across the Blombos Cave southern section (Fig. 1), that come from distinct anthropogenic combustion features, identified in section, from two layers of the M2 lower phase. Sample 1 from layer CGABh1, quadrant G7b, which is dated to 82 kya (total station ref: 2688) and Sample 2 from layer CGAC, quadrant G7b, which is dated to 85 kya (total station ref: 2728) (see Fig. 1). It is likely that these combustion events are remnant hearths that may have been either trampled and/or cleaned.
To establish that the route into the archaeological record was anthropogenic and that the manner of deposition was consistent with processing and cooking, we considered whether burrowing animals, other organic deposits (possibly aeolian) or other anthropogenic activity could have been responsible for these assemblages
The most likely taxa that would burrow in this cave would be Procavia capensis (Rock hyrax), which occur in the vicinity of Blombos today and Bathyergus suillus (Cape dune mole rat). Both species have a diet that is dominated by grasses and sedges, although B. suillus also eat bulbs and tubers. Neither species store food underground. Only B. suillus nests underground 14–16. Both species defecate and urinate in outside latrines, which can sometimes be metres thick and which are visible to the naked eye in the archaeological record 17,18. Any assemblage attributable to either of these burrowing animals would contain a significant number of phytoliths and no phytoliths were present in this assemblage. We have, therefore, dismissed this possibility.
There are organic deposits with humified remains and these have the appearance of combustion features in section but contain no/very few charred plant remains of any kind. It is possible that this vegetation may have blown into the cave, as has significant amounts of sand. These deposits may account for three unsuccessful samples out of the ten (see Table S.3, S.I.). Humified plant remains have little identifiable cell structure and provide a clear contrast with samples that contains a high density of charred plant remains with clear cell structures in a close spatial context, as with the samples discussed in this paper.
The other route into the archaeological record may be attributed to plants, such as sedge grasses, used by hunter-gatherers as bedding. Occasionally, the rhizomes and tubers remained attached to these grasses when gathered and used as bedding as at Sibudu Cave 19,20. The bedding was then burned as part of a periodic cleansing of the cave leaving charred rhizomes and tubers. This scenario leaves a distinctive archaeological signature of long burned layers in the stratigraphy, or if not burned, then long white layers created by phytoliths from decomposed sedge grass stems, both visible at Sibudu Cave 20. At Sibudu the parenchyma from these rhizomes and tubers has perfectly preserved cell structure, indicating they had dried before burning. This is not the case at Blombos and no phytoliths were found in the SEM process.
The density of charred starchy plant fragments recovered from these two contexts (see Results - Table S.3 in the S.I.) were significantly higher, forming around 40% of all charred plant fragments in the sample, compared to the zero presence and low density of parenchyma fragments in the control sample and non-combustion event samples. This result attests to the likelihood of these samples coming from an anthropogenic combustion event and that their presence was not accidentally tracked or trodden into the cave, where the density is likely to have been more random and less spatially concentrated.
That these combustion events may have been used for cooking food is supported by the presence of other anthropogenic evidence, including vertebrate remains and three lithic fragments, the latter also coated in burned sediment and ash.
Finally, the evidence of the fragments themselves. The ‘folded’ appearance of the root and tuber cell structure is the unique result of the starchy tissue being pounded when fresh. This pounded tissue was then mixed with pounded seeds and cooked. Only humans are known to cook and use this multi-step processing prior to cooking 21.