Grooming of conspecifics is thought to play an important social role among nonhuman primates, but the function and relative importance of such grooming among humans is unknown. Here the authors compare time spent grooming and conversing among six small-scale societies with grooming data from 69 nonhuman primate species. They test the hypothesis that conversation evolved among humans as an alternative way to obtain the social benefits (such as building and maintaining social alliances) of grooming in large groups.

The researchers examine associations between male status and various measures of reproductive success among foraging/non-foraging, and monogamous/polygynous societies in order to test the "egalitarian hypothesis" which predicts lower status effects in hunter-gatherer groups. Contrary to this hypothesis, they find that male social status is equally significantly associated with reproductive success in foraging and nonforaging societies. Additional support is found for the "mating effort" hypothesis, which predicts that male reproductive success will be more associated with fertility than offspring mortality in polygynous societies, leading the authors to make various suggestions regarding the evolutionary mechanisms at play.

The research examines daily food sharing norms of 73 preindustrial societies from the Standard Cross-Cultural Sample. Multilevel regression models reveal that hunting and less predictable environments are not indicative of everyday food sharing, but offer support for many other predictions. Animal husbandry, external trade, daily labor sharing, and the presence of food storage are all predictive of daily food sharing practices whereas sharing is less common amongst large and stratified societies. These results align with evolutionary theories for food sharing practices.

Researchers examine marriage patterns of 186 societies from the Standard Cross-Cultural Sample (SCCS). The eleven predictor variables are pathogen stress, arranged female marriages, population density, father roles during infancy, temperature, social stratification, wealth inequality, internal warfare, assault frequency, female agricultural contribution, and sex ratio. The two outcome variables measuring polygyny are cultural rules constraining polygyny and the percentage of married men who are polygynous. Controlling on phylogeny using a global supertree of the languages, analysis of marriage patterns reveals that assault frequency and pathogen stress are the strongest predictors of polygyny. These findings offer additional support for the theories of harem-defense polygyny and male genetic quality.

This article is mainly concerned with understanding the motivators toward egalitarianism through modeling via a game that combined elements from both hawk-dove and prisoners dilemma. While most of the article is focused on this model, the researchers also tested their hypotheses cross-culturally on a sample of forager societies. In both cases, they found evidence that the benefits of cooperation drove egalitarianism.