Disease, CCR5-[DELTA]32 and the European Spread of Agriculture? A Hypothesis

Article excerpt

From its origins in the Starcevo-Koros culture of the Hungarian Plain around 5700 BC the Neolithic archaeological assemblage of the Linearbandkeramik (LBK) spread within two centuries to reach Alsace and the middle Rhine by 5500 BC, though the rapidity of the spread makes it difficult to measure using available radiocarbon evidence (Dolukhanov et al. 2005). In this same time period, during the Terminal Mesolithic, c. 5800 to 5500 BC, there is evidence for forager-herder-horticulturists in Central and Western Europe prior to the appearance of the LBK (Gronenborn 1999, 2009). The Cardial Neolithic complex spread round the shores of the northern Mediterranean from southern Italy to Portugal in the period 5700-5400 BC.

Unfavourable climate change may have facilitated the rapid LBK spread, but seems insufficient to explain the magnitude and speed of this transition (Gronenborn 2009). Population density of Mesolithic groups would have been crucial, and the earliest LBK settlements were in areas of deciduous forests and loess soils considered scarcely visited by Mesolithic foragers, as evidenced by the paucity of Terminal Mesolithic sites in Central Europe (Luning et al. 1989). By contrast, areas where LBK did not spread readily tend to correspond with demonstrable Mesolithic occupation, including north-west France, the North European Plain and southern Scandinavia. The speed of LBK spread thus appears correlated with low density Late Mesolithic population. Iri the Mediterranean, the Cardial similarly bypassed areas of Mesolithic settlement and often occupied areas with little Mesolithic habitation.

A hypothesis for low Terminal Mesolithic populations is the introduction of new diseases such as smallpox, measles, brucellosis and influenza into Europe with incoming Neolithic populations (Wolfe et al. 2007; Barnes et al. 2010). Those diseases known as 'zoonoses' may have been derived through domestic livestock living in close and regular proximity with humans in substantial populations (Weiss 2001; Armelagos & Harper 2005; Wolfe et al. 2007). Such conditions arose during the eighth or seventh millennium BC at settlements such as Catalhoyuk in southern Turkey, which probably housed several thousand inhabitants (Cessford 2005). Spreading Neolithic farming populations may then have carried these diseases across Europe.

Mediterranean Europe may also have been affected by zoonoses spreading through hunter-gatherer populations in advance of the spread of farming. In the Adriatic, the number of sites declined sharply in the Late Mesolithic (Biagi & Spataro 2002), and along the northern shore of the western Mediterranean there is usually a stratigraphic gap of several centuries or more between Mesolithic and Neolithic (Perrin 2005; Forenbaher & Miracle 2006; Guilaine & Manen 2007).

Following on from the Mesolithic--Neolithic transition in the Near East or Anatolia, an Early Neolithic population would subsequently have undergone expansion and, in association with increased population density, seen the development of outbreaks of communicable diseases (Diamond & Bellwood 2003). Some resistance would have been likely to have evolved through increased allelic variation of the major histocompatibility complex in members of this population in response to the pathogens concerned (Gluckman et al. 2009). If previously unexposed, the European Mesolithic population would have no such protection. Though the differences in susceptibility were probably not as great as for the North American colonisation (Dobyns 1966; Diamond & Bellwood 2003; Wolfe et al. 2007), such diseases might still have devastated Terminal Mesolithic populations.

Though some diseases, such as tuberculosis, are observable from archaeological skeletal remains (Roberts & Buikstra 2003), most zoonoses are not so detectable, even by ancient DNA analysis (Barnes & Thomas 2006). There is, nevertheless, evidence of rapid selection for genetic resistance to one or more of these diseases during the last 7000 years or so (Wolfe et al. …