Chimps may be aware of others’ deaths

Captive and wild apes react in intriguing ways to losing comrades

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HANGING ON A chimp mother in Bossou, Guinea, climbs a tree for food while carrying her dead infant. Tatyana Humle
Pansy the chimpanzee died surrounded by friends and family who cared for her as best they could and reacted to her demise with silent somberness. Pansy’s story, as well as those of two mothers unable to let go of their deceased infants, raises the possibility that chimpanzees know when a companion has died and realize that he or she will never return, two new studies report in the April 27 Current Biology . “Chimpanzees may have greater awareness of the finality of death than has previously been believed,” says psychologist James Anderson of the University of Stirling in Scotland, who directed the study of Pansy’s death. Pansy’s case provides the first glimpse of chimps’ responses to a companion’s natural death, Anderson says. Two video cameras in an indoor enclosure at a safari park recorded what happened before and after Pansy’s death on December 7, 2008. In the days before Pansy’s demise three adult chimps, including her daughter, groomed her regularly. Grooming increased as Pansy’s breathing became labored in the 10 minutes preceding death. A male chimp stood over Pansy’s lifeless body and pulled at her left arm and then tried to open her mouth. He jumped onto the platform where Pansy lay and charged in an aggressive display. After pounding on Pansy’s body, he ran off. The next day, the three chimps watched silently as keepers removed Pansy’s body. None of them slept on Pansy’s deathbed for five days. For several weeks, survivors did little and ate less than usual. “These incidents strengthen the inference that apes have some sort of conception of death,” says chimp researcher William McGrew of the University of Cambridge in England. Primatologist Frans de Waal of Emory University in Atlanta has seen similar reactions to companions’ deaths in captive chimp colonies and calls Anderson’s report “completely believable.” Anderson says it may be more humane to allow elderly apes to die among companions in research facilities and zoos, rather than isolating them for treatment or euthanasia. In the wild, chimps’ reactions to a dead comrade or infant vary greatly from one individual to another, much as in people, comments Elizabeth Lonsdorf of Lincoln Park Zoo in Chicago. Old and sick chimps often find sheltered spots to die alone or get taken by predators, with the group resuming its daily foraging. “We don’t know yet if chimps can grieve for the loss of a group member,” Lonsdorf remarks. Uncertainty also surrounds the intentions of two female chimps that literally wouldn’t let go of infants that died of infections in 2003, as described in another study. These chimps inhabited forests surrounding Bossou, Guinea. One female, the mother of several other chimps, carried her 1-year-old on her back while foraging for 68 days. The other female, a first time mother, carried her 2-year-old in the same way for 19 days. Then the bodies were abandoned. In both instances, tropical weather dried and preserved the corpses in a natural mummification process. Mothers groomed infants’ bodies and took them into their day and night nests. Over time, mothers increasingly let other group members, including youngsters, handle and play with the bodies. Zoologist Dora Biro of the University of Oxford in England, who led the study, is cautious about interpreting the behavior as reflecting an awareness of death. “These mothers understood that there was something unusual about their infants, but whether for them that indicated that the infants would never come back to life remains a fascinating open question,” Biro says. A member of Biro’s team observed another Bossou chimp carrying her dead infant for several weeks in 1992. Ape mothers’ refusal to let go of dead infants makes evolutionary sense, de Waal says. Close emotional ties to one’s youngster prevent chimp mothers from prematurely abandoning sick and near-dead infants, in his view. “Chimpanzees may know something of someone else’s mortality, but we have no way of knowing whether they understand their own mortality,” de Waal remarks.
Bruce Bower

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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