Malthusian assumptions lead to Boserupian phenology in a global model of the transitions to agriculture

In the many transitions from foraging to agropastoralism it is debated whether innovation in technology or increase of population is the primary driver. The driver discussion traditionally separates Malthusian (technology driven) from Boserupian (population driven) theories. I present a numerical model of the transition to agriculture and discuss this model in the light of the population versus technology debate and in Boserup’s analytical framework in development theory. Although my model is based on ecological—Neomalthusian— principles, the coevolutionary positive feedback relationship between technology and population results in apparent Boserupian behaviour: innovation is greatest when population pressure is highest. This outcome is not only visible in the theory-driven reduced model, but is also present in a corresponding “real world” simulator which was tested against archaeological data, and which thus demonstrates the relevance and validity of the coevolutionary model. The lesson to be learned is that not all that acts Boserupian needs Boserup at its core. 1 Transitions to agriculture The relationship between humans and their environment underwent a radical change during the last 10000 years: from mobile and small groups of foraging people to sedentary extensive cultivators and on to high-density intensive agriculture modern society turned the formerly predominantly passive human user of the environment into an active component of the Earth system. The most striking global impact is only visible and measurable during the last 150 years (Crutzen and Stoermer, 2000; Crutzen, 2002); much earlier, however, the use of forest resources for metal smelting from early Roman times and the medieval extensive agricultural system had already changed the landscape (Barker, 2011; Kaplan et al., 2009); the global effects of these early extensive cultivation and harvesting practices are yet under debate (Ruddiman, 2003; Lemmen, 2009; Kaplan et al., 2011; Stocker et al., 2011). ∗Chapter manuscript submitted to “Society, Nature and History: The Legacy of Ester Boserup” 15th August 2011 1 ar X iv :1 10 8. 25 85 v1 [ qbi o. PE ] 1 2 A ug 2 01 1 Transitions to agriculture occurred in almost every region of the world, earliest in China and the Near East over 9000 years ago (Kuijt and Goring-Morris, 2002; Londo et al., 2006), and latest in Australia and Oceania with the arrival of Polynesian and European immigrants few hundred years ago (Diamond and Bellwood, 2003). While each local transition can be considered revolutionary, the many diverse mechanisms, environments, and cultural contexts of each agricultural transition make it difficult to speak of the one ‘Neolithic revolution’, as the transition to farming and herding was termed by V. G. Childe almost a century ago (Childe, 1925). The transition from foraging to farming was not only one big step, but may have consisted of many intermediary stages: Bogaard (2005) looks at the transition in terms of the land use systems: she sees first inadvertent cultivation then horticulture then simple and then advanced agriculture, while Boserup (1965) discriminates these stages by the management practice ranging from forest, bush and short fallow to annual and multi cropping. Studies of contemporary hunting-gathering societies showed that much less time has to be devoted to procuring food (Sahlins, 1972) than with agriculture, and that much less labour is required Boserup (1965) for long fallow systems compared to intensive multi-cropping agriculture. So why farm? While many different answers have been given to this question from archaeology (Barker, 2011), demography (Turchin and Nefedov, 2009) historical economy (Weisdorf , 2005), and ecosystem modeling (Wirtz and Lemmen, 2003), possibly the simplest relationship was proposed by Malthus (1798), who expressed the dynamics between population and food productivity as a reciprocal: more people meant more food production, more production enabled higher populations. Malthus’ reciprocal relationship constitutes a positive feedback loop, which ideally results in ever greater (geometric) growth and productivity increases; that this is not the case in a world with finite resources was expressed by Malthus (1798) by stating that “Population, when unchecked, increases at a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison with the second.”; Malthus identified the need for positive and preventive checks to balance population increase with the limited capacity of resources. How does an increase in productivity come about? First and foremost, the input of more labour increases productivity as stated by Malthus (1798). While he focused on this extensive and inherent productivity increase, the intensification component of productivity increase was highlighted by Boserup (1965). Investments in a more intensive production system would— however—require large additional labour, and the benefits of such investments were often small. To stimulate an investment in more intensive agriculture, Boserup requires population pressure. Both Malthus (1798, 1826) and Boserup (1965, 1981) concentrate on the role of labour (and later division of labour and social/family organisation) and neglect the role of labourindependent innovation; these are not storage or tools (which requires labour for harvesting, building, and tool processing), but rather innovations in the resources themselves, such as cultivation of higher-yielding grains or imported high yield varieties, or their management (such as water rights); this distinction may not unambiguous for some innovations, but is used here for simplification. Labour-independent innovation can be stimulated by diversity in (and thus size of) a population (Darwin, 1859, p. 156): Aggregation is a motor of technological and