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Studies probe chimps’ awareness of death

April 26, 2010
Courtesy of Cell Press
and World Science staff

Two new stud­ies of­fer rare glimpses in­to how chim­panzees deal with the deaths of those clos­est to them, sci­en­tists say.

Chimps’ “aware­ness of death is prob­ably more highly de­vel­oped than is of­ten sug­gested. It may be re­lat­ed to their sense of self-awareness, shown through phe­nom­e­na such as self-recognition and em­pa­thy,” said said James An­der­son of the Uni­vers­ity of Stir­ling in the U.K., who col­la­bo­rat­ed in one of the stud­ies. 

A chimp moth­er uses a twig to swat flies away from her dead in­fan­t's body at Bos­sou, Guin­ea, in this still from a vid­eo. The chimp had died two days ear­li­er of a res­pi­ra­to­r dis­ease. The moth­er went on car­ry­ing the corpse for 19 days. (Cour­tesy Cell Press)


In that re­search, An­der­son and col­leagues de­scribed the fi­nal hours and death of an old­er fe­male chimp liv­ing in a small group at a U.K. sa­fa­ri park as cap­tured on vid­e­o. In the oth­er stu­dy, sci­en­tists watched as two chimp moth­ers in the wild car­ried their in­fants’ mum­mi­fied re­mains for weeks af­ter they were lost to an ill­ness.

Re­search­ers have posted vid­e­os from both stud­ies on­line. Both stud­ies are pub­lished in the April 27 is­sue of the jour­nal Cur­rent Bi­ol­o­gy.

Few have wit­nessed chimps’ re­sponse at the mo­ment a mem­ber of their group dies, An­der­son said. Moth­er chimps have been known to car­ry their dead in­fants, he noted, and some ob­servers have seen the com­mo­tion that fol­lows when an adult chimp is lost to some sort of sud­den trau­ma.

“In con­trast to the fren­zied, noisy re­sponses to trau­matic adult deaths, the chim­panzees wit­ness­ing the fe­male’s death in our case were mostly calm,” An­der­son said.

In the days lead­ing up to the old­er chim­p’s death, the group was very qui­et and paid close at­ten­tion to her, the re­search­ers re­port. Right be­fore she died, she re­ceived much groom­ing and ca­ress­ing from the oth­ers, who seemed to test her for signs of life as she died. They left her soon af­ter, but her adult daugh­ter re­turned and re­mained by her moth­er all night, sci­en­tists said. When keep­ers re­moved the moth­er’s body the next day, the chim­panzees re­mained sub­dued and stayed that way for some time. For sev­er­al days they avoided sleep­ing on the plat­form where the fe­male had died, though it was nor­mally a fa­vored sleep­ing spot.

“In gen­er­al, we found sev­er­al si­m­i­lar­i­ties be­tween the chim­panzees’ be­hav­ior to­ward the dy­ing fe­male, and their be­hav­ior af­ter her death, and some re­ac­tions of hu­mans when faced with the de­mise of an eld­erly group mem­ber or rel­a­tive,” An­der­son said.

In the sec­ond stu­dy, Do­ra Bi­ro of the Uni­vers­ity of Ox­ford and her col­leagues wit­nessed the deaths of five mem­bers, in­clud­ing two in­fants, of a sem­i-i­so­lat­ed chimp com­mun­ity that re­search­ers have been stu­dying for over three dec­ades in forests around Bossou, Guin­ea.

“We ob­served the deaths of two young in­fants—both from a flu-like res­pi­ra­to­ry ail­ment,” Bi­ro said. “In each case, our ob­serva­t­ions showed a re­mark­a­ble re­sponse by chim­pan­zee moth­ers to the death of their in­fants: they con­tin­ued to car­ry the corpses for weeks, even months, fol­low­ing death.”

In that time, the corpses mum­mi­fied com­plete­ly, and the moth­ers showed care of the bod­ies rem­i­nis­cent of their treat­ment of live in­fants: they car­ried them ever­ywhere dur­ing their daily ac­ti­vi­ties, groomed them, and took them in­to their day and night nests dur­ing rest times, Bi­ro said. Over this ex­tend­ed pe­ri­od, they al­so be­gan to “let go” of the in­fants grad­u­al­ly, Bi­ro added. They al­lowed oth­er group mem­bers to han­dle them more and more often and tolerat­ed long­er pe­ri­ods of separa­t­ion from them, in­clud­ing in­stances where oth­er in­fants and ju­ve­niles were al­lowed to car­ry off and play with the corpses.

Oth­er group mem­bers showed some in­ter­est in the bod­ies, and al­most none showed any aver­sion to­ward the corpses, ac­cord­ing to Bi­ro and col­leagues. She not­ed that a mem­ber of her team made very si­m­i­lar ob­serva­t­ions fol­low­ing the death of one chim­pan­zee in­fant in Bossou back in 1992.

“Chim­panzees are hu­mans’ clos­est ev­o­lu­tion­ary rel­a­tives, and they have al­ready been shown to re­sem­ble us in many of their cog­ni­tive func­tions: they em­pa­thize with oth­ers, have a sense of fair­ness, and can co­op­er­ate to achieve goals,” Bi­ro said. “How they per­ceive death is a fas­ci­nat­ing ques­tion, and lit­tle da­ta ex­ist so far” con­cern­ing it.

“Our ob­serva­t­ions con­firm the ex­istence of an ex­tremely pow­er­ful bond be­tween moth­ers and their off­spring which can per­sist, re­mark­ably, even af­ter the death of the in­fant, and they fur­ther call for ef­forts to elu­ci­date the ex­tent to which chim­panzees un­der­stand and are af­fect­ed by the death of a close rel­a­tive or group-mate. This would both have im­plica­t­ions for our un­der­standing of the ev­o­lu­tion­ary ori­gins of hu­man per­cep­tions of death and pro­vide in­sights in­to the way chim­panzees in­ter­pret the world around them.”


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Two new studies offer rare glimpses into how chimpanzees deal with the deaths of those closest to them, scientists say. Chimps’ “awareness of death is probably more highly developed than is often suggested. It may be related to their sense of self-awareness, shown through phenomena such as self-recognition and empathy,” said said James Anderson of the University of Stirling U.K., who collaborated in one of the studies. In that research, Anderson and colleagues described the final hours and death of an older female chimp living in a small group at a U.K. safari park as captured on video. In the other study, scientists watched as two chimp mothers in the wild carried their infants’ mummified remains for weeks after they were lost to a respiratory epidemic. Researchers have posted videos from both studies online. Both studies are published in the April 27 issue of the journal Current Biology. Few have witnessed chimps’ response at the moment a member of their group dies, Anderson said. Mother chimps have been known to carry their dead infants, he said, and some observers have seen the commotion that follows when an adult chimp is lost to some sort of sudden trauma. “In contrast to the frenzied, noisy responses to traumatic adult deaths, the chimpanzees witnessing the female’s death in our case were mostly calm,” Anderson said. In the days leading up to the older chimp’s death, the group was very quiet and paid close attention to her, the researchers report. Right before she died, she received much grooming and caressing from the others, who seemed to test her for signs of life as she died. They left her soon after, but her adult daughter returned and remained by her mother all night, scientists said. When keepers removed the mother’s body the next day, the chimpanzees remained subdued and stayed that way for some time. For several days they avoided sleeping on the platform where the female had died, though it was normally a favored sleeping spot. “In general, we found several similarities between the chimpanzees’ behavior toward the dying female, and their behavior after her death, and some reactions of humans when faced with the demise of an elderly group member or relative,” Anderson said. In the second study, Dora Biro of the University of Oxford and her colleagues witnessed the deaths of five members, including two infants, of a semi-isolated chimpanzee community that researchers have been studying for over three decades in the forests surrounding Bossou, Guinea. “We observed the deaths of two young infants—both from a flu-like respiratory ailment,” Biro said. “In each case, our observations showed a remarkable response by chimpanzee mothers to the death of their infants: they continued to carry the corpses for weeks, even months, following death.” In that time, the corpses mummified completely, and the mothers showed care of the bodies reminiscent of their treatment of live infants: they carried them everywhere during their daily activities, groomed them, and took them into their day and night nests during periods of rest. Over this extended period, they also began to “let go” of the infants gradually, Biro said. They allowed other group members to handle them more and more frequently and tolerated longer periods of separation from them, including instances where other infants and juveniles were allowed to carry off and play with the corpses. Other group members showed some interest in the bodies, and almost none showed any aversion toward the corpses, according to Biro and collagues. She noted that a member of her team made very similar observations following the death of one chimpanzee infant in Bossou back in 1992. “Chimpanzees are humans’ closest evolutionary relatives, and they have already been shown to resemble us in many of their cognitive functions: they empathize with others, have a sense of fairness, and can cooperate to achieve goals,” Biro said. “How they perceive death is a fascinating question, and little data exist so far concerning chimpanzees’ responses to the passing of familiar or related individuals either in captivity or in the wild. “Our observations confirm the existence of an extremely powerful bond between mothers and their offspring which can persist, remarkably, even after the death of the infant, and they further call for efforts to elucidate the extent to which chimpanzees understand and are affected by the death of a close relative or group-mate. This would both have implications for our understanding of the evolutionary origins of human perceptions of death and provide insights into the way chimpanzees interpret the world around them.”