In 2003, in the deep forests of Bossou in Guinea, a chimpanzee mother did something that reshaped how we view animal minds. Jire carried the the lifeless body of her one-year-old infant Jimato for some 68 days. Even as the infant mummified before her, she gently swatted flies away, carefully placed it on branches while she ate, and cradled it as she moved through the canopy and forest ground.

Carrying a deceased infant is an extraordinary physical commitment. Imagine trying to go about your everyday life, navigating difficult terrain, securing food, and keeping up with your family in a forest, while bearing the weight of a lost infant. It restricts how you move and demands constant mental vigilance.

Yet, despite this immense physical and psychological toll, chimpanzee and bonobo mothers frequently refuse to let go. Indeed, the example of Jire and Jimato is eclipsed by a case from the Mahale Mountains, Tanzania, where a mother carried her infant’s corpse for perhaps as long as 126 days.

To understand why chimpanzee and bonobo mothers do this, we analysed 83 cases across 15 chimpanzee and bonobo communities. We discovered that this behaviour is remarkably widespread. It seems to be a fundamental part of how these apes deal with the death of their young.

The strongest pattern we found concerned the cause of death. Mothers carried infants that had died from disease for much longer than infants killed by other chimpanzees. A fatal illness can create........

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