Male-biased operational sex ratios and the Viking phenomenon: an evolutionary anthropological perspective on Late Iron Age Scandinavian raiding

By Ben Raffield, Neil Price and Mark Collard

Evolution and Human Behavior (forthcoming)

Abstract: In this paper, we use a combination of evolutionary theory, ethnographic data, written sources, and archaeological evidence to develop a new explanation for the origins of Viking raiding. Our argument focuses on the operational sex ratio, which is the ratio of males to females in a society who are ready to mate at a given time. We propose that a combination of two practices – polygyny and concubinage – and the increase in social inequality that occurred in Scandinavia during the Late Iron Age resulted in a male-biased operational sex ratio. This would have created a pool of unmarried men motivated to engage in risky behaviours that had the potential to increase their wealth and status, and therefore their probability of entering the marriage market. With high-status men looking to instigate expeditions to acquire plunder and develop their reputations as war leaders, raiding represented a mutually beneficial means of achieving social advancement and success.


Introduction: Shipborne raiding by Scandinavian groups is central to our understanding of the Viking Age (c.750–1050), but the causes of this phenomenon remain uncertain. A wide range of explanatory factors has been put forward, including environmental change, overpopulation, and innovations in sailing technology. However, as Barrett has argued, these suggestions are not especially convincing because they lack supporting data and/or only consider short-term triggers. In this paper, we use evolutionary theory and ethnographic evidence in combination with archaeological data and textual sources to develop a new explanation for the early raids, which began in the late 8th century. Specifically, we explore the possibility that they may have been prompted in part by the existence of certain forms of male–female relationship that motivated men to obtain status, wealth, and captives, and to engage in risky behaviour such as raiding in order to do so.

Conceptually, our hypothesis is related to what is perhaps the oldest explanation for Viking raiding, which was put forward by Dudo of St. Quentin (c. 965–1043). In History of the Normans, he argued that the raids were caused by an excess of unmarried young men. Early modern scholars revived this notion several centuries later. For example, in Camden’s (1610) volume Britannia, he suggested that the “Wikings” were selected by lot from among the young men of an overpopulated area and sent abroad to avoid civil strife, after they had “multiply’d themselves to a burdensom community”. In time, the idea that raiding was a result of a surplus of single men became something of a cliché among scholars of the Viking Age, though Barrett has recently suggested that it deserves more careful consideration.

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