Original Research Article Climatic Variability and the Population Dynamics of Historical Hunter–Gatherers: The Case of Sami of Northern Finland SAMULI HELLE 1 * AND SAMULI HELAMA 2 1 Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland 2 Department of Geology, University of Helsinki, FI-00014 Helsinki, Finland ABSTRACT Our current knowledge on climate-mediated effects on human population dynamics is based on preindustrial agrarian societies where climate-induced crop failures had a major impact on fertility and mortality rates. However, because most of the human evolutionary history has been shaped by hunter–gatherer lifestyle relying on diverse plant and animal food sources, it is also important to understand how climate affected the population dynamics of hunter–gatherers. We thus studied whether climate, measured as a reconstructed annual mean temperature, had concurrent or delayed effects on the key components of population dynamics, annual births and deaths, in three historical (1722–1850) Sami populations of Northern Finland that depended mainly on fishing, hunting, and reindeer herding for their livelihood. We found only weak concurrent effects of mean temperature on annual births and deaths, although in general warm years correlated with increased birth and reduced mortality rates. Likewise, tem- perature-mediated delayed effects were mainly absent: in one population only, a warm previous year tended to reduce the number of births. By contrast, annual numbers of births and deaths were more closely associated, as indicated by negative correlations between births and deaths up to three previous years. To summarize, in contrast to historical agrarian societies, the population dynamics of historical Sami seemed to be only weakly associated with annual mean temperature, which may indicate that these populations, probably due to their dietary breadth, were rather unaffected by climatic variation. Am. J. Hum. Biol. 19:844–853, 2007. ' 2007 Wiley-Liss, Inc. Births, deaths, and migration determine the size and growth rate of open populations (Turchin, 2003; Yaukey and Anderton, 2001) and prevailing environmental conditions can have profound effects on all of these factors. For example, food shortage because of abiotic hazards can increase mortality, reduce fertil- ity, and induce migration (Ottersen et al., 2001; Scott and Duncan, 2002; Scott et al., 1998; Stenseth et al., 2002). Hence, environ- mental conditions play an essential role in population dynamics. Together with intrinsic biological processes, i.e., direct and delayed density-dependence, extrinsic factors can pro- duce large temporal and spatial variation in population abundance (Turchin, 2003). Abiotic environment can influence demo- graphic parameters directly and indirectly (Galloway, 1986; Lee, 1987; Richards, 1983). Adverse environmental conditions, such as heat and cold shocks, UV-radiation from the sun, and diverse extreme weather events, can directly increase mortality and reduce repro- duction (McMichael et al., 2006; Patz et al., 2005). The indirect environmental effects instead include, for example, effects on the prevalence and species richness of infectious diseases and on diverse food sources, like cul- tivation, animal husbandry, and water supply, that affect mortality and fertility (Guernier et al., 2004; Koelle et al., 2005; McMichael et al., 2006; Patz et al., 2005). The magnitude of such effects may depend on the characteristics of populations, as some populations may be better buffered against adverse and unpredictable environmental haz- ards. For example, less developed societies depending mainly on one climate-sensitive sub- sistence are likely to be the most vulnerable to fluctuations in environmental conditions. This Contract grant sponsor: The Academy of Finland; Con- tract grant number: 207270; Contract grant sponsor: Foun- dation of Koneen Sa ¨a ¨tio ¨. *Correspondence to: Samuli Helle, University of Turku, Department of Biology, Yliopistonma ¨ki 1, FI 20014 Turku, Finland. E-mail: sayrhe@utu.fi Received 4 October 2006; Revision received 29 December 2006; Accepted 30 January 2007 DOI 10.1002/ajhb.20650 Published online 21 August 2007 in Wiley InterScience (www.interscience.wiley.com). AMERICAN JOURNAL OF HUMAN BIOLOGY 19:844–853 (2007) V V C 2007 Wiley-Liss, Inc.