AUTHOR=Cacault M. Paula , Goette Lorenz , Lalive Rafael , Thoenig Mathias 

TITLE=Do we harm others even if we don't need to?

JOURNAL=Frontiers in Psychology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2015.00729

DOI=10.3389/fpsyg.2015.00729

ISSN=1664-1078

ABSTRACT=<p>Evolutionary explanations of the co-existence of large-scale cooperation and warfare in human societies rest on the hypothesis of parochial altruism, the view that in-group pro-sociality and out-group anti-sociality have co-evolved. We designed an experiment that allows subjects to freely choose between actions that are purely pro-social, purely anti-social, or a combination of the two. We present behavioral evidence on the existence of <italic>strong aggression</italic>—a pattern of non-strategic behaviors that are welfare-reducing for all individuals (i.e., victims and perpetrators). We also show how strong aggression serves to dynamically stabilize in-group pro-sociality.</p>