Researchers in judgment under uncertainty have argued that biases, fallacies, and framing effects explain much of the apparently nonfunctional variation in human decision-making. In contrast, evolutionary researchers have shown that human decision-making is well-engineered (ecologically rational) when the standard is adaptive performance on evolutionarily recurrent tasks (e.g., Wang, 1996; Cosmides & Tooby, 1996; Rode, et al., 1999; Brase, et al., 1998; Gigerenzer & Selton, 2001). My research builds on this approach and explores the context- and domain-specificity of adaptations for risky decision-making, such as the social context of male intrasexual competition for status via resources (Ermer et al., 2008).

Natural selection acting on our ancestors is expected to have equipped the human mind with evolved mechanisms that were designed to register the impact of an individual’s behaviors on the welfare of others, and to regulate their choices based on estimates of this impact. These decisions are hypothesized by to be regulated by a welfare tradeoff ratio, a summary index determined by combining myriad factors that affect the payoffs to valuing the welfare of another individual. These factors include relative formidability (Sell, 2005), kinship (Lieberman et al., 2007), relative status, ability to confer benefits, relationship history (if any), shared goals, social alliances, coalitional formidability, and others. My research investigates coalition-derived formidability as a component of welfare tradeoff ratios. Using methods from experimental economics and psychology, we are exploring how coalitional support regulates people’s resource allocation decisions and judgments of entitlement (Ermer, 2007).

Engaging in social exchange and taking precautions to mitigate hazards are distinct adaptive problems. Cognitive and patient studies indicate that reasoning about these two domains is regulated by two different, functionally distinct mechanisms (Fiddick et al., 2000; Stone et al., 2002). If social exchange and precautionary reasoning are caused by neurally distinct mechanisms, there should also be evidence of this in normal, brain-intact individuals. Using fMRI, we found different patterns of neural activation in response to Wason tasks involving social exchange, precaution, and descriptive rules (Ermer et al., 2006). Furthermore, areas associated with theory of mind (anterior and posterior temporal cortex) were engaged when people were reading and interpreting social exchange rules, but not precautionary rules. My current work is exploring the brain basis of different aspects of social exchange reasoning in normal subjects using imaging, and dissociation of reasoning abilities in brain-damaged and split brain patients.