Fig 1.
Heating techniques compared by this study.
a: Above-ground heating in a fire; b: Above-ground heating with the ‘pile of embers’ technique; c: Underground heating in a sand-bath; d: Underground heating in an earth-oven like fire-pit.
Fig 2.
Definition and graphic code of structural elements in cognigrams.
These symbols are: perception of need/problem; operational step; phase of activities; direction of process and problem perceptions; foci; tools; effects and other conceptual cognitive components (based on [31, 32, 60, 63]).
Fig 3.
Cognigram of above-ground heat treatment in a fire.
The cognigram is based on archaeological evidence and experiments conducted by Schmidt et al. [33].
Fig 4.
Cognigram of above-ground heat treatment with the ‘pile of embers’ technique‘.
The cognigram is based on archaeological evidence and experiments conducted by Schmidt et al. [33].
Fig 5.
Cognigram of underground heat treatment in a sand-bath.
The cognigram is based on archaeological [45] and ethnographic evidence (see for example: [56–58]).
Fig 6.
Cognigram of underground heat treatment in earth-oven like fire-pit.
The cognigram is based on archaeological evidence [46].
Fig 7.
Complexity-indices of heat treatment techniques.
Graph of the number of foci (active and passive), phases, steps and effects as well as the total number of elements (n total) and complexity-indices (mean) for the four heating techniques (underground: earth-oven like fire-pit, sand-bath; above-ground: ash-embers-cone and pile of embers). Underground heating techniques show higher complexity indices than above-ground heat treatment. Complexity indices for the heating techniques are: earth-oven like fire-pit: 7.33 (mean value of 10 foci (4 active and 6 passive), 13 steps, 7 phases and 4 effects; sand-bath heating: 7 (mean value of 9 foci (3 active and 6 passive), 13 steps, 7 phases and 4 effects; camp-fire: 3.33 (mean value of 4 foci (3 active and 1 passive), 6 steps, 4 phases and 2 effects; pile of embers: 4.83 (mean value of 5 foci (3 active and 2 passive), 9 steps, 5 phases and 4 effects.
Fig 8.
Problem-solution distances (expressed as complexity-index) of 19 Middle Stone Age techniques and the four heat treatment techniques.
Techniques involving conceptual cognitive components are labelled as such: subject-initiated effect (SiE), composition (+) and technological symbiosis ({). a: Diagram of the problem-solution distance (complexity-index: average of the number of active foci, passive foci, phases, steps and effects; and conceptual cognitive components) of 19 MSA techniques and the four heating techniques. Heat treatment with the ‘pile of embers’ technique lies roughly in the middle of the 23 techniques. Above-ground heat treatment in a fire is one of the less complex techniques. Underground heat treatment is among the most complex techniques but still in the range of MSA complexity. 13 techniques involve a SiE, 7 techniques composition and one technique technological symbiosis. b: Diagram of the temporal perspective on the complexity of the 19 MSA techniques and the four heat treatment procedures. Nearly all techniques with higher complexity indices than above-ground heating appear later in the current archaeological record of the MSA than above-ground heat treatment or their age is yet unknown. Only fire making predates early silcrete heat treatment. Above-ground heating techniques and probably fire making are the oldest techniques including a SiE (data extracted from [3, 6, 11, 12, 14–16, 45, 46, 64, 66–76]).