The Tongan Maritime Expansion: A Case in the Evolutionary Ecology of Social Complexity

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The evolution of the Tongan maritime empire, involving both the development of social complexity and geographic expansion through conquest and trading, are examined by means of evolutionary ecology. This Darwinian evolutionary framework provides the mechanism and identifies the environmental structure, processes, and behavioral strategies by which to account for the geographic and temporal pattern of change in Tonga and related islands. Both ethnohistorical and archaeological data are employed in this analysis, showing how both may reveal overlapping aspects of historical change. The results of this research highlight the importance not only of competition but also of cooperative strategies in the evolution of social complexity and the process of geographic expansion. Key to explaining the evolution of Tongan social complexity are the productive but uncertain environment of Tongatapu, the location of Tongatapu in relation to other islands and prevailing winds, the small landmass of the island, the relatively early integration of the island into a single polity, the creation of collateral ruling lineages, the appropriation of voyaging technology to redirect competition from within Tongatapu to other islands through colonization, aggression, staple and wealth goods trade, and the exchange of spouses. KEYWORDS: evolution of social complexity, evolutionary ecology, Tongan maritime complex, Polynesian archaeology, ethnohistory.

PACIFIC ISLAND scholars have long pondered the origin of Polynesian "complex chiefdoms" and their political expansion throughout remote Oceania (e.g., Goldman 1955, 1970; Goodenough 1957; Sahlins 1958, 1963; Williamson 1924). Among archaeologists, social stratification, the increasing authority of elites, and territorial integration in Polynesia (and especially Hawai'i) have been variously explained as resulting from population growth, agricultural intensification, and the control over material and ideological domains by leaders in ecologically sensitive island environments--conditions that may give rise to competition and conflict through expansionist warfare and the geographical extension of polities (e.g., Cordy 1981; Earle 1991; Hommon 1976; Kirch 1984, 1988a, 1990a; Kirch and Green 1987; Kolb 1991, 1994; Suggs 1961; Tuggle 1979). These views parallel, in part, the work of Carneiro (1970, 1972), Flannery (1972), and Harris (1979), who argue that phenomena such as warfare and agricultural intensification are cultural mechanisms designed to counter social instabilities caused by population pressure, limited resources, and ecological degradation and which at the same time promote social complexity. Particularly for Pacific Island archaeologists, changes in insular ecology extrapolated from the paleoenvironmental and archaeological records present ideal "laboratory conditions" to explain agricultural intensification, demographic changes, and subsequent social stratification and conflict (e.g., Clark and Terrell 1978; Kirch 1984, 1997). Developed within the framework of a generalizing science of cultural evolution, this remains the dominant mode of interpretation employed by much of the Americanist archaeological community in the Pacific.

A number of researchers, however, have acknowledged that while ecological settings and their influence on humans are significant conditions to explain the proximate causes leading to political stratification and territorial integration (i.e., through conflict or cooperation), they alone (or even as more abstract generalizations) cannot provide an explanation for the ultimate causes leading to the emergence and persistence of complex societies (e.g., Cachola-Abad 1998; Graves and Sweeney 1993; Graves and Ladefoged 1995; Ladefoged 1993a, 1995). In our view, explanations for the development of complex chiefdoms in Polynesia can be explained best by a Darwinian model that focuses on the aggregate results of individual competitive and cooperative behavioral strategies (rather than those of populations) that provide them with selective advantages over other members within or across social groups. …