Beyond life-history plasticity: Reconsidering environmental harshness and unpredictability as determinants of human cooperative strategy

Abstract

Human cooperation has mostly been explained with the theory of reciprocal altruism, in which return is essentially delayed. A body of life-history psychology literature, therefore, articulates that individuals who grew up in adverse environments should be less cooperative as they tend to develop a phenotype with present-oriented traits. However, little to no supportive evidence, especially in the domain of dyadic cooperation, has been yielded in those studies. Considering the risk-pooling utility of the system of reciprocity and theoretical findings on social coalition, the present pre-registered study explores an untested, yet informed, alternative possibility: While environmental unpredictability may undermine the incentive to cooperate, harsh but stable ecologies foster cooperative phenotypes. A sex-balanced sample of 799 young adults (mean age = 20.8) was recruited to participate in a one-shot prisoner's dilemma. Consistent with preexisting reports, across experimental conditions, childhood environmental harshness, childhood environmental unpredictability, and their interaction all do not predict less cooperation. Directly compared to those who had a harsh and unpredictable childhood, individuals that grew up in harsh but stable environments were, as hypothesized, more cooperative, in unprimed conditions. Descriptive analysis shows that in the conditions, harshness was correlated to increased cooperation and perceived unpredictability was correlated to decreased cooperation in the low unpredictability group and the high harshness group respectively. Surprisingly, while priming of current adversity threat led to a general increase in cooperation, those who grew up in harsh but stable ecologies instead switched from the most to the least cooperative in response to the identical cue, showing significantly less cooperation compared to both the rest of the sample and their unprimed selves. Thus, the preliminary findings suggest that childhood environmental adversity may promote cooperativeness in certain circumstances and likely calibrate cooperative strategy with more sophistication than previously argued in the literature. Re-examination of the influences of environmental adversity on human cooperation is warranted.