Data from: The nasty neighbour effect in humans

Like other group-living species, humans often display parochial
cooperation, that is they cooperate with ingroup members more than with
outgroup members and strangers. Theoretically, parochial cooperation
should imply that people also compete less with ingroup members than with
outgroup members and strangers. However, in situations where people could
invest to take other’s resources, and invest to protect against such
exploitation, we observed the opposite pattern. Akin to what in other
species is known as the ‘nasty neighbour effect’, in such dyadic contests
people invested more (rather than less) with ingroup members than with
out-group members and strangers across 51 nations, in different
communities in Kenya, and in on-line samples from the United Kingdom. This
‘nasty neighbour’ behaviour emerged independent of parochial cooperation
and trust towards others that have the same (versus different) nationality
and, fitting field-observations in other species, neighbour nastiness
emerges when people perceive within-group resource scarcity, and
especially towards low-ranking ingroup members. That humans can exhibit
both parochialism and nastiness within groups is difficult to reconcile
with existing theories on the evolution of cooperation in structured
populations.