UvA

Humans empathize with others (Batson, 1998), form long-term attachments to close others (see Chapter 1, this volume), and sacrifice their immediate self-interests to promote the overarching interests of the groups and communities they belong to (Dawes, 1980; Komorita & Parks, 1995; Ostrom, 1998; see also Chapter 19, this volume). These and related tendencies indicate that humans are a cooperative species (Bowles & Gintis, 2011; Nowak, Tarnita, & Wilson, 2010) and fit the idea that throughout evolution, prosocial behavior promotes the functioning of the individual’s ingroup, which in turn provides for levels of security and prosperity well beyond what individuals could possibly achieve alone (Darwin, 1873; Henrich & Henrich, 2007; Wilson, 2012). If these claims about humans’ sociality are true, it stands to reason that group affiliation has its roots in evolved neurobiological systems and circuitries. Here I pursue this possibility by focusing on emerging streams of research, from my own laboratory and those of others, on the role of brain oxytocin (OT). OT is a nine-amino-acid neuropeptide that functions as both a hormone and a neurotransmitter (Donaldson & Young, 2008; see also Chapters 1, 3, and 8, this volume) and has a well-documented role in reproduction and pair-bond formation (e.g., Carter, Grippo, Pournajafi-Nazarloo, Ruscio, & Porges, 2008). Here I argue and show that its functions are broader and include a range of social behaviors that promote the functioning of an individual’s group, including the tendency to protect the ingroup through competitive reactions to threatening outsiders. The starting point is a model (De Dreu, 2012a) delineating how hypothalamic release of OT modulates two critical functions underlying parochial cooperation, namely, ingroup trust and concern for (members of) the ingroup. Subsequent sections review the research evidence for these propositions and the implication that OT also motivates noncooperation toward rival outgroups. The final section summarizes the main conclusions and identifies avenues for new research into the link between OT and the regulation of intra- and intergroup relations.