Video: Chimps carry corpses
In a forest clearing in the far south-east of Guinea, a mother chimpanzee gently puts down her baby so that she can crack open a nut. There’s something wrong with the apparently mundane scene, though: her baby is dead, and has been for weeks.
The 1-year-old chimp, known as Jimato, died of flu when an epidemic struck a community of 19 chimps living in the district of Bossou in 2003. The virus also killed 2-and-a-half-year-old Veve. Both corpses were carried by their mothers for weeks.
Such behaviour has been seen in primates before, but rarely. What’s unusual in these cases is how long the mothers clung onto their young. In other accounts of corpse-carrying primates, the body has been snatched out of the mother’s hands by rowdy males, or in wet conditions it has disintegrated within days. But the dead Jimato and Veve were carried for 68 and 19 days respectively before they were abandoned.
Their bodies were effectively mummified by dry-season conditions. “They dried out and lost all of their hair, leaving most of the body parts, even the genitals, preserved in a layer of dry, leathery skin,” says Dora Biro at the University of Oxford, who has co-authored a paper on the behaviour.
Another new study looks at how a group of captive chimpanzees dealt with the death of an elderly female. Together, these episodes have given insights into how chimpanzees deal with death, and what finally causes the mothers to let go of their dead young.
James Anderson, a psychologist at the University of Stirling, UK, has written about the death of Pansy, the captive, elderly female chimp. After Pansy’s death, her daughter stayed beside her throughout the night. Then members of the chimp group cleaned the corpse and avoided the place where she died. Anderson says these may be “rituals” to cope with death.
On the other hand, he says, “Biro’s results suggest that a period of continued contact after the death of an infant may be important for a mother chimpanzee to adjust psychologically to her loss”.
“Our combined research makes a strong case that chimps not only understand the concept of death but also have ways with which they cope with it,” says Anderson.
In many ways, the mothers in Biro’s study treated the corpses as though they were still alive: they groomed them, swatted flies away, emitted high-pitched screams of distress when they accidentally dropped the bodies and placed them on the ground “with great gentleness and care, as though they were alive”, says Biro.
But some of their behaviour suggests they knew that the corpses were dead. For instance, “when an infant called Fokaye playfully dragged a corpse around a tree, his mother flinched and moved away”, says Biro. “But that’s the only time we saw a chimp show aversion.”
Eventually, both Bossou mothers did abandon their dead young, which Biro thinks is linked to their hormonal cycle. Chimps produce hormones that prevent them from getting pregnant while they’re breastfeeding: as soon as they stop, fertility returns within 14 to 77 days.
“The hormonal changes the chimps experience as their bodies gear up to reproduce may push them into ‘letting go’ of the corpses,” says Biro. “We don’t know that for sure, but our observations suggest that may be true.”
One question that remains is why the chimpanzee mothers carry their dead infants, given that the corpses make it hard for the mothers to climb trees and feed themselves. Frans de Waal, a primatologist based at Emory University in Atlanta, Georgia, says it may be an extension of looking after sick infants. “The infant may recover,” he says.
Alternatively, corpse-carrying may have become something of a Bossou “tradition”, says Biro. She believes that Veve’s mother may have learned to carry her dead infant from Jimato’s mother, who performed the behaviour twice (PDF) before Veve died.
Journal references: Biro: Current Biology, vol 20, p R351; Anderson: Current Biology, vol 20, p R349
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