Verbal and non-verbal vocal cues of co-operation and competition were assessed in 120 freely-formed dyadic conversations. In line with previous research, female/female dyads were found to be the most cooperative. However, in female/female conversations, cooperation decreased, and non-verbal competition increased, when males were present. Male/male conversation did not exhibit significant changes in style when a female audience was present. Mixed-sex conversations showed evidence of compromise between the two conversational styles; however, females were still significantly more cooperative in conversational style than males, and males exhibited higher levels of verbal competitiveness than females.
We show that human subjects are sensitive to the influence of both the risks associated with investments and the influence of relatedness when deciding whether or not to invest in relatives. However, there were significant differences between subjects, with some preferring to emphasise risk while others preferred to emphasise kinship. Subjects who were better at assessing probabilities were more likely to identify risky investments, while those who were better at handling conjoint probabilities were more likely to take both kinship and risk into account.