A peacock’s tale: runaway agricultural evolution and the development of pre-pottery Neolithic communities in the southern Levant

Abstract

A runaway model of agricultural evolution was developed to account for patterns of development and sustainability among the Pre-Pottery Neolithic societies of the southern Levant, and to provide insights into contemporary patterns of development and sustainability. A Darwinian theory of subsistence evolution was developed from first principles, framed in terms of cultural transmission or dual-inheritance theory. An approach to sustainability was formulated in terms of niche construction theory and resilience thinking. Adaptive models from human behavioural ecology (e.g. optimal foraging theory and nutritional ecology) and cultural transmission theory (e.g. cultural group selection and tribal social instincts) were scrutinised, and shown to be inadequate for modelling the evolution of early agriculturally-dependent societies. A maladaptive model of runaway agricultural evolution was developed, and a series of preconditions and predictions were derived. These preconditions and predictions were assessed against early Holocene archaeological and palaeoenvironmental records from the southern Levant. Data from more than 50 archaeological sites spanning more than 3000 years was examined across a range of disciplines, materials and methodologies, including: archaeobotany, zooarchaeology, osteology, genomics, palaeodemography, palaeopathology, site catchment analysis, palaeoenvironmental reconstruction, mortuary practices, architecture, material culture and stone tools. A distinctive pattern of development was identified, involving: increasing agricultural investment, increasing ritual investment, demographic growth, increasing social differentiation and inequality, the accumulation of sustainability problems, the accumulation of sustainability solutions, the possible evolution of formal regulative social institutions, and the erosion of social-ecological resilience leading to ‘niche cracking’. Socio-political and economic relationships critical to the instigation and maintenance of runaway agricultural evolution could have rendered LPPNB societies particularly vulnerable to disruption, triggering a de-escalation or reverse runaway. The most plausible triggers to the LPPNB/PPNC release (Ω) and reorganisation (α) appeared to be climate change, crop disease or anthropogenic landscape alteration. The runaway model sufficiently explained numerous dimensions of the PPN archaeological and palaeoenvironmental records in the southern Levant. A number of predictions received strong support (e.g. patterns of agricultural investment, demography and ritual performance and the development of sustainability problems and solutions) and others existed at the limits of archaeological detectability (e.g. the development of LPPNB regulatory social institutions). The idea that sustainability problems elicited genetic responses from PPN populations, and that those responses generated problems of their own, received precursory support from recent genome-wide SNP and WGS data, constituting particularly auspicious areas of future research. The runaway model could plausibly be extended to explain dominant patterns of Holocene socioeconomic development – e.g. patterns of increasing socioeconomic complexity, agricultural dispersals, the ‘origins of the state’, and even present-day patterns of sustainability and development.