Economic Specialisation, Resource Variability, and the Origins of Intensive Agriculture in Eastern Africa

Introduction Eastern Africa has long been renowned for its highly specialised pastoralists (Gulliver, 1955; Herskovits, 1926; Hollis, 1905; Spencer, 1965). However, it is only in more recent years that recognition has grown of the extent and accomplishments of the region’s ‘specialist’ agriculturalists, as evidenced by the growing body of literature on Eastern African ‘islands of intensive agriculture’ (Sutton, 1989c; Widgren, 2000; Widgren and Sutton, 2004; Stump, 2006a; Stump, 2010; Davies, 2008; Davies, 2012). These ‘islands’ are highly productive in contrast to surrounding ‘seas’ of lower productivity and less intensive land use such as shifting cultivation and pastoralism. They are distinctive in displaying considerable investments in land and technology, including integrated systems of irrigation, hillside terracing, and other soil management strategies. These systems are further surprising in that they fall not in areas of higher rainfall, but rather within or on the margins of semi-arid areas, with paradoxically high population densities. The development of these ‘islands of intensive agriculture’ has long posed a challenge to archaeologists, geographers and historians alike. One solution has been to treat them as independent, discrete, and historically situated events (Amborn, 1989; Anderson, 1989; Anderson, 1988; Börjeson, 2004a; Börjeson, 2004b; Loiske, 2004; Östberg, 2004; Sheridan, 2002). The other, of course, has been to look for patterns of behaviour that cross-cut ethnic and linguistic divisions and which represent similar responses to similar environmental and economic stimuli (Boserup, 1965; Håkansson, 1989; Gourou, 1991, as cited in Widgren, 2004; Widgren, 2004). Neither approach is mutually exclusive; however, I argue here that similar patterns of behaviour can be identified within a number of regions and that these patterns result from broadly similar underlying ecological processes. The Eastern African environment, particularly the Rift Valley region, presents dramatic variations in geology, soils, topography, rainfall, and vegetation that lend themselves well to economic specialisation (Kusimba and Kusimba, 2004: 397). Traditionally this specialisation has been enshrined in the distinction between pastoralists and agriculturalists, however, in recent decades a growing body of literature has pointed out the fallacy of this dichotomy. ‘Pure’ agriculturalists and ‘pure’ pastoralists represent extremes (at times short-lived) along a continuum of various fluid and shifting economic practices (Anderson and Johnson, 1988: 10; Spear and Waller, 1993; Spencer, 1998; Waller, 1988: 111). Furthermore, it is now commonly recognised that, rather than being self-contained economic systems, agricultural and pastoral economic activities are intricately entwined. Dense exchange and kin relations criss-cross economic and ethnic boundaries throughout the region (Håkansson, 1994; Håkansson, 2004; Håkansson, 2008; Håkansson and Widgren, 2007; RESEARCH