Demographic modelling. We have developed a technique (Shennan et al. 2013; Manning and Timpson 2014), which allows us to investigate changes in human demography using a Monte Carlo Summed Probability Distribution (MCSPD) method, which assesses the density of 14C dates as a proxy for relative population size. We have recently demonstrated a major and rapid demographic increase between 10,500 and 5500 BP (Manning and Timpson 2014), which clearly corresponds to the Holocene AHP. Building on this, we will undertake a systematic collection of all 14C dates, combined with the proposed programme of compound-specific 14C dates, which will increase the number of existing Saharan Holocene radiocarbon dates by nearly 20%, in order to increase the resolution of our demographic proxy and to investigate key events highlighted in the pilot study. For example, our initial study revealed an apparent fall and rise in population levels between 7500 and 6500 BP, which we hypothesised may relate to a replacement of early Holocene hunter-gatherer-fisher groups, with later Holocene pastoral populations deriving from the eastern Sahara. Spatial analysis of the 14C dates will test this by estimating temporal fluctuations in the total area covered (both at the macro scale, and within regions), and temporal fluctuations in clustering patterns. In particular we will calculate regional variations in the timing of population increase and decrease, and investigate the evidence for population displacement between neighbouring regions. By providing a high temporal resolution proxy for effective carrying capacity our demographic curve also offers an independent estimate of environmental change in northern Africa, indicating a temporal delay in the terrestrial response to atmospheric climate change. These results highlight the degree to which human demography is a function of environment at the appropriate scale of observation in both time and space and provides strong support for the efficacy of this method in the context of North Africa.
Demography and Human Adaptation
Figure 1. Demographic proxy based on a Monte-Carlo Summed Probability Distribution of radiocarbon dates from Neolithic Saharan sites (Manning and Timpson 2014)
Identification of biomarkers for the processing of aquatic commodities, animal fats and plant resources. An important methodological component of our work will be to detect specific marker compounds for the processing of fish and other aquatic products to assess the role of freshwater resources in the diet of early Holocene Saharan populations, i.e. testing the “Aqualithic” hypothesis. Our recent identification of stable compounds formed from the transformation during cooking of diagnostic aquatic lipids, including dihydroxy acids (DHYAs), isoprenoid acids (IPAs) and ω-(o-alkylphenyl) alkanoic acids (APAAs), offers the possibility for highly sensitive and large-scale detection of aquatic product processing in archeological pottery (Cramp and Evershed 2014).
Figure 2. Encrusted ceramic residue © Julie Dunne
Figure 3. Partial gas chromatograms of trimethylsilylated total lipid extracts (TLEs) from potsherds excavated from Takarkori rock shelter showing leaf wax n-alkanes and plant fatty acids.
Biomolecular and carbon isotopic analysis of food residues to determine modes of animal exploitation. Recent work by Dunne et al. (2012) demonstrates the potential for applying biomolecular techniques in the context of Saharan prehistory, most notably in providing evidence for the adoption of dairying by Libyan Saharan pastoralists by at least 6500 BP. We will use the compound-specific stable carbon isotope approach to individual fatty acids to identify the major classes of domesticates, ruminants and non-ruminants, together with dairy fats (see Palaeoenvironment page). The signals will be used, in conjunction with the palaeohydrological results, to map spatial and temporal trends in the adoption of domesticates and development of dairying economies across the Sahara.