Abstract
Different hypotheses identifying factors affecting the complexity of implements used to obtain food resources by hunter-gatherer groups are assessed with regression analysis. A regression model based on interaction between growing season as a proxy measure for risk and number of yearly moves fits data on the complexity of implements for 20 hunter-gatherer groups. The interaction model leads to a division of hunter-gatherer groups into two subgroups that correspond to collector vs. forager strategies for procuring resources. Implications of the interaction model for the evolution of complex implements are discussed.