Fig. 1.

(A) Effects of intergroup conflict with and without in-group affiliation on urinary oxytocin levels in wild chimpanzees in East and South groups (n = 468 samples, 20 subjects, 296 events). (B) Effects of imminent intergroup conflict in East group chimpanzees on urinary oxytocin levels (n = 52 samples, 9 subjects, 43 events). Shown are medians (thin horizontal lines), quartiles (boxes), percentiles (2.5 and 97.5%; vertical lines), minimum and maximum (laying crosses), as well as the fitted model and its 95% confidence intervals (thick lines). ***P < 0.001, **P < 0.01, *P < 0.05.