Some chimpanzees seem to grieve similarly to humans in the face of a fellow chimp's death, two new studies have found, appearing to comfort the dying, experience trauma after death and have trouble letting go.
The research, published Monday in the journal Current Biology, provides a window onto a less public aspect of primate life, the authors said.
In one study, researchers at the University of Stirling and at Blair Drummond Safari Park in Britain watched how three chimpanzees, kept in heated indoor quarters during the winter, reacted as a fourth chimp, an elderly female named Pansy, sickened and died.
Park officials had separated Pansy from the other chimpanzees for treatment when she became ill in November 2008. But when her breathing became erratic a few weeks later, the other three chimps were allowed to join her.
In the 10 minutes before she died, the three animals – an elderly female named Blossom, Blossom's adult son Chippy and Pansy's adult daughter Rosie – frequently groomed and caressed Pansy. They crouched in close, and Chippy shook her arm, apparently testing for signs of life.
When they got no reaction, "they appeared to arrive at a collective decision that something had changed, and she was no longer the same as she was beforehand," said lead author
, who studies primate behavior at the University of Stirling. "It seems they are clearly able to distinguish the difference between being alive and unresponsive."
Soon, both Blossom and Chippy left Pansy's side. Even though it was not her usual sleeping area, Rosie stayed by her mother's corpse almost the entire night, sleeping fitfully.
Sixteen hours after Pansy's death, zookeepers removed the body, with the three chimps watching quietly. For several days afterward, the group was subdued, refusing to make a nest on the platform where Pansy had died. They also demanded more attention from the keepers.
"I'm not going to say chimpanzees have a human understanding of death – chimps are chimps and humans are humans – but we were immediately struck during the video by the phenomena we observed," Anderson said, "because we know chimpanzees are capable of a wide range of emotions very much akin to human emotions."
Anderson said he hoped this would prompt zookeepers to reevaluate the common practice of removing terminally ill animals from a group. In some ways, he said, it may be more humane to allow the group to remain together until a sick animal dies, to give the ailing animal comfort and allow the group a sense of closure.
In the second study, chimpanzee mothers were observed in the forests of Bossou, Guinea, after a disease swept through a clan of 19 chimpanzees, killing five, including two infants. The mothers of those infants continued to carry the corpses around, even as the bodies swelled, then gradually dried out.
Other studies had described this phenomenon, researchers said, but this was unique in the length of time it took for the mothers to abandon the bodies. One mother carried her baby for 19 days; another mother carried hers for 68 days.
"We have two explanations here – one is that there is a very, very strong bond between chimpanzee mothers and chimpanzee infants," said lead author Dora Biro, a biologist at the
. Biro theorized that chimpanzee mothers had evolved to become extremely attached to their babies "because chimpanzee primates are born completely helpless, like humans."
"Another possibility is that they were aware of the death and this was just their way of dealing with it," Biro added, pointing to humans' inability to let go of objects that remind us of people we have lost.
To better understand the mothers' awareness of death, Biro said, the researchers would have had to witness the infants' actual moment of death. "It's possible there would have been some response, like stress or fear or anger, but we weren't there to see it."
, co-director of the
Research Center, called the studies' findings interesting, but said that although humans and chimpanzees shared similar emotions to some degree – fear, anger, empathy – it would be dangerous to extrapolate too much about chimps' perception of death.
He recalled a time he saw a few chimpanzees come across an antelope with its belly sliced open, its contents devoured. Stanford said "they used the empty rib cage … as a playhouse for a couple hours. So if they're pushing a corpse around, it's not something understood."