The study of animal grief is a young field, largely because studies of any animal behaviors that one might think of as “human” were ignored for much of the twentieth century. It was commonly held that nonhuman animals were only reactive beings, lacking thoughts and emotions, and responding to stimuli as unthinking, unfeeling robots. Scientists were cautioned about being anthropomorphic, that is, regarding animals as they are often depicted in naive films and storybooks—as if they were people dressed up in fur or feathers. Researchers who thought they detected animal emotions—especially those that we think of as uniquely human, such as love, joy, or grief—were considered to be sentimentalists. And their reports (such as Darwin’s about the grieving cows) were dismissed as anecdotal.

In the last few decades, though, wildlife biologists have amassed so many firsthand accounts of animals caring for and mourning their dead that the idea of animal grief is no longer as suspect as it once was. Two recent books, both published in March of this year, explore the subject. How Animals Grieve, by anthropologist Barbara J. King, collects anecdotal and scientific data on grief in many kinds of animals, even some that most researchers ignore, such as rabbits, goats, and turtles. In The Bonobo and the Atheist, primatologist Frans de Waal examines the biological roots of religion and morality. Since our awareness of death is often cited as the reason we developed religion, de Waal investigates whether other animals have a similar sense of their ultimate end. While King doubts that even our close chimpanzee relatives are “aware that death is coming,” de Waal suggests that older apes or elephants may have experienced enough of life to comprehend that they, too, will die. “When an old ape notices that trees are harder and harder to get into or an elephant has ever more trouble keeping up with the herd, might these individuals not apply what they have learned about life and death to their own bodies?” de Waal asks. “It’s hard to know, yet impossible to rule out.”