Do chimpanzees (Pan troglodytes) console a bereaved mother?

Abstract

Comparative thanatology encompasses the study of death-related responses in non-human animals and aspires to elucidate the evolutionary origins of human behavior in the context of death. Many reports have revealed that humans are not the only species affected by the death of group members. Non-human primates in particular show behaviors such as congregating around the deceased, carrying the corpse for prolonged periods of time (predominantly mothers carrying dead infants), and inspecting the corpse for signs of life. Here, we extend the focus on death-related responses in non-human animals by exploring whether chimpanzees are inclined to console the bereaved: the individual(s) most closely associated with the deceased. We report a case in which a chimpanzee (Pan troglodytes) mother experienced the loss of her fully developed infant (presumed stillborn). Using observational data to compare the group members' behavior before and after the death, we found that a substantial number of group members selectively increased their affiliative expressions toward the bereaved mother. Moreover, on the day of the death, we observed heightened expressions of species-typical reassurance behaviors toward the bereaved mother. After ruling out several alternative explanations, we propose that many of the chimpanzees consoled the bereaved mother by means of affiliative and selective empathetic expressions.

Keywords: Bereavement; Chimpanzees; Consolation; Empathy; Thanatology.

Fig. 1

Timeline of events described in the current study, on 30-01-2018 observations occurred outside of the regular schedule and no observations took place on 31-01-2018. Observations resumed on 01-02-2018, excluding Tushi who was held in the backstage enclosures with the infant’s corpse. On 02-02-2018, the infant’s corpse was removed and Tushi reunited with the rest of the group

Fig. 2

Mean hourly rates of received affiliation predicted by the GLMM (accounting for estrus state and location of observations) plotted per month and contrasted to the actual received affiliation. The vertical line indicates the stillbirth of the infant

Fig. 3

Percentage change in mean hourly rates of affiliation received by each individual in the month before (January) and after (February) the death of the infant as predicted by the model, using January as 100%

Fig. 4

Actual and model estimate of mean hourly rate of affiliation directed towards Moni and Jimmie by each individual in the group per month. The vertical line indicates the stillbirth of the infant