Chimpanzees have remarkably complex, even human-like, responses to the deaths of their closest companions, new research suggests.
Two separate studies published this week in the journal Current Biology document how chimps reacted to the deaths of others, in one case an elderly chimp in captivity and in the other, the sudden deaths of babies.
Researchers at the University of Stirling in the U.K., led by James Anderson, examined the behaviour of adult chimps living in a small group at a safari park in Scotland after an elderly female died.
Pansy was more than 50 years old when she died in 2008. She lived on an island in Blair Drummond Safari Park with her daughter, and another adult female and her son.
The reactions of the chimps to Pansy's death were recorded on the park's cameras.
The researchers found that in the days leading up to Pansy's death, the group paid close attention to her, grooming and caressing her. After she died, members of the group appeared to check her for signs of life by lifting her arms and looking into her mouth.
The young male attacked the corpse, in an attempt, the researchers said, to revive her, or in an expression of anger or frustration.
The group left soon after Pansy died, but her adult daughter returned and spent the night with her. The next morning, the chimps removed straw that was covering Pansy's body.
As zoo workers removed Pansy's body, the group sat quietly and watched. They avoided sleeping on the platform where she had died, even though it was normally the chimps' preferred sleeping spot.
The chimps' behaviour was starkly different, the scientists said, to previous anecdotes of reaction to death, which described noisy alarm calls and aggressive displays, even cannibalism.
While biologists tend to avoid attributing human standards and emotions to animal behaviours, the researchers were struck by the similarity to human reactions to the death of loved ones.
"In general, we found several similarities between the chimpanzees' behaviour toward the dying female, and their behaviour after her death, and some reactions of humans when faced with the demise of an elderly group member or relative, even though chimpanzees do not have religious beliefs or rituals surrounding death," Anderson said in a statement.
Mother chimps seem to mourn infants
In the other study, researchers led by Dora Biro of the University of Oxford observed the deaths of five chimps in a community in Guinea from a flu-like respiratory disease.
Two of the chimps who died were infants.
"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," said Biro.
In those weeks, the babies' corpses mummified and the mothers continued to carry them with them and groom them as if they were alive.
After more time passed, the mothers eventually "let go" of the infants, allowing other chimps to handle them.
Biro said that although humans don't carry deceased infants in this way, the chimp behaviour was similar to human feelings of refusing to "let go" after a loved one dies.
"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," she said.
Anderson said that the finding, both at the Scottish zoo and in the wild, show that behaviours that were once thought to set humans apart from other animals can be seen in our closest relatives, including awareness of death.
"The findings we've described, along with other observations of how chimpanzees respond to dead and dying companions, indicate that their awareness of death is probably more highly developed than is often suggested," said Anderson.
"Science has provided strong evidence that the boundaries between us and other species are nowhere near to being as clearly defined as many people used to think," he said.