Figure 5. Mean ± SE (boxes) R indices within the two female vs. female categories.

Whiskers indicate the 95% confidence interval of the means. NM-M: dyads consisting of non-mother and mothers; NM-NM: dyads consisting of non-mothers. The value of R index in dyads consisting of non-mother and mother was positive (mean R ± SE = 0.28±0.02) showing that mothers received more grooming from non-mothers than they gave in return. The dyads of non-mothers represented approximately symmetry on the amount of time they invested in grooming each other within each dyads (mean R ± SE = 0.01±0.09).