No effect of inter-group conflict on within-group harmony in non-human primates

It has been a longstanding assumption that the threat of extra-group conflict can promote the expression of socio-positive behavior and cohesion within animal groups. I conducted a comparative analysis on the effect of inter-group conflict (indexed by home range overlap) on within-group affiliation levels (indexed by time engaged in allogrooming) in a sample of 48 primate species. There was no association between the 2 variables in a phylogenetic generalized least squares regression. I conclude that inter-group conflict may at best elicit short-term immediate changes in affiliation levels, but permanently elevated cohesion appears unique to humans with their large-scale social integration and scaled up inter-group conflict.