A primate's response to death

And as our understanding of other living creatures grows, we realize that humans are not the only ones whose behavior changes in the presence of death. Known today as 'Comparative Thanatology', researchers extensively study the cognitive, psychological, and physiological aspects of death among non-human animals.

In the first in-depth review on comparative thanatology in primates, André Gonçalves of Kyoto University's Primate Research Institute and Susana Carvalho of Oxford University analyzed over 200 years of documentation on non-human primates interacting with their dead. Bringing together the diverse field of comparative thanatology, the findings include an evolutionary timeline of mortuary practices, and covers fields from archeology to psychology. The report was published in Biological Reviews.

Observations and anecdotal evidence both in the wild and in captivity go as far back as the 19th century. Gonçalves reports that while certain responses differ between primate species, common behaviors are observed: primates defended dead companions against threats, carried their dead, and even exhibited emotional responses that can be described as 'grief'.

"Although these earlier anecdotes are anthropomorphic, the behavioral patterns are consistent to what is observed today," he says.

The team compiled and reviewed an extensive record of 240 reports to fulfill three primary goals: documenting history, collecting and interpreting the current data, and developing an evolutionary frame-work of death responses in primates.

"Non-human primates exhibit all sorts of behavior related to death, one of the most prevalent are mothers carrying their dead offspring. Many factors contribute to this behavior, but we find that they do it because they have the ability to grasp objects," continues Gonçalves. "Interestingly, primates such as lemurs or tamarins do not engage in this behavior despite continued attempts. We find that this is because they lack that same grasping ability."

When an adult member dies, a different set of patterns are observed, such as holding vigils, and guarding or visiting the body. The team reports that these interactions likely come as a by-product of attachment relationships. They also infer that this allows the primates to learn vital information from the corpses, serving as a way to re-categorize the individual from living to dead -- an essential part of the grieving process -- and informing on potential shifts in the group's hierarchy.

Moreover, the team proposes that non-human primates are capable of an implicit awareness of death.

"It's not an all-or-nothing ability. Awareness of death includes things such as animate/inanimate distinction, or the sensory and contextual discrimination of living/dead," Gonçalves explains. "The concept of death is something we humans acquire between ages 3 to 10. We can infer that non-human primates have some aspects of death awareness but, thus far, only humans conceptualize it at a higher order."

While a few anecdotes suggest great apes may indeed have a concept of death like humans, Gonçalves and Carvalho state the need to formulate and test hypotheses in experimental settings.

The team intends to apply this comprehensive review to further their research in comparative thanatology, and hopes other scientists will explore different avenues of research to uncover our unique perspective of death.