Data on the frequency of non-reproductive adults in a cross-cultural sample of small-scale human societies

The goal of this brief communication is to report crosscultural data with relevance to researchers studying cooperative breeding in humans in the context of other non-human mammals. The data are derived from ethnographic research in 36 small-scale human populations/ cultural groups living on 5 continents. A number of recent accounts have described Homo sapiens as a species that practices cooperative breeding [e.g., Hill and Hurtado (2009); Hrdy (2009); Kramer (2010); Mace and Sear (2005); van Schaik and Burkart (2010)]. These claims raise two important questions: first, do humans in general, or humans under a specific set of conditions, exhibit behaviors conforming to the technical definition of cooperative breeding? And second, to what extent are patterns of behavior and reproduction in humans similar to, or distinct from those found in non-human animals that are classified as cooperative breeders? These questions has been addressed in part through individual empirical cases studies (Hagen and Barrett, 2009; Hill and Hurtado, 2009; Kramer, 2005; Meehan et al, 2013; Strassmann, 2011) and theoretical papers (Burkart et al, 2009; Smaldino et al, 2013). They remain difficult to answer rigorously, however, without cross-cultural data (Hill et al, 2011; Kramer, 2010). While cooperative breeding is defined as adults exhibiting costly behaviors that typically increase the fitness of other adults, a likely consequence of such behavior is likely to be a pool of non-reproductive