Could a chimpanzee be guilty of murder?

Rene Descartes (1596 -1650), the French philosopher and mathematician, famously declared that animals are mere automata, operating like clockwork machines. However, we now know that animals have an inner emotional life and some even seem to have a rudimentary sense of right and wrong. And science correspondent Ginny Smith (The Psychologist, August 2016) even ponders whether moral blame can be assigned in some circumstances to animals closely related to humans.

Elephants are very social animals and we know that when a popular member of a troop dies, the surviving elephants seem to mourn the departed, bury the corpse under vegetation, maintain a graveside vigil for about a week and return to visit the bones annually.

There is some evidence that rats show empathy for each other although this evidence can be difficult to interpret. Peggy Mason (Science, December 2011) described how rats help companions in distress. Rats were first housed in pairs for some weeks to allow a bond to develop between the two. Now a pair of rats was placed in a walled arena, one rat allowed to roam freely but the other rat constrained in a transparent tube openable only from the outside. Initially the free rat, sensing the fear of the trapped rat, behaves warily but gradually overcomes the fear, approaches the trapped rat and nuzzles at the walls of the transparent tube. Eventually after several days he/she learns that the door of the constraining tube opens by pressing on it, freeing the trapped rat. Over time the freely roaming rat releases its trapped companion almost immediately after being placed in the arena.

Our closest animal relatives are the great apes – chimpanzees, orangutans and gorillas – and we expect that their inner lives more closely resemble our own inner lives than do more distantly related animals. For example, 95 per cent of human DNA is identical to chimpanzee DNA, meaning we are as closely related to chimps as the horse is to the zebra.

Ginny Smith cites evidence that chimpanzees mourn their dead. Chimpanzees have been observed shaking and thumping dead companions as if trying to revive them, or grooming the dead body and swatting flies away. Mother chimps sometimes carry their dead babies around for several days. Chimps also seem to show compassion, although only to members of their own troop. If a chimp is attacked, his/her friends will hold and groom him/her when the attack is over.

Chimpanzee society is relatively violent and it is not uncommon for one chimp to kill another. For example, a member of a rival group is often attacked near the boundary line dividing the two groups. The question arises, do chimpanzees have a sense of morality and know that this behaviour is wrong – is this murder? This question was discussed at The Times 2016 Cheltenham Science Festival and is described by Ginny Smith.

Murder is defined as the killing with intent of a reasonable being, not in self-defence. Is a chimpanzee a reasonable being? Some chimp behaviour seems to show a sense of morality. A higher-ranking chimp will not take something by force from a lower-ranking chimp and if one chimp steals food from another, the second chimp punishes him.

But can the chimpanzee understand right from wrong sufficiently to be accused of murder? Ginny Smith points out that human children under the age of 10 cannot be found guilty of murder because we believe they do not understand right from wrong. Most estimations of chimpanzee intelligence would not score higher than a six-year-old human child. On the other hand, chimps seem good at forward planning, something children struggle with. Smith tells the story of a chimp in a zoo hiding rocks from his keeper at night so he can enjoy his favourite morning pastime – throwing rocks at visitors.

On balance it seems unjustifiable to judge fatal violence among chimpanzees on the same basis as we judge human violence. On the other hand we can discern the glimmering of incipient morality in the animal kingdom, glimmerings that later seeded the evolution of moral codes in human society.

William Reville is an emeritus professor of biochemistry at UCC, http://understandingscience.ucc.ie