麻豆传媒

The 3-month-old baby was snatched from its mother鈥檚 arms, killed by a bite to the forehead and eaten. The act was carried out by a mother and daughter who were members of the same close-knit community as the baby. They were later implicated in at least two other cases of infanticide and cannibalism.

By any standards of morality, this killing spree would be labelled 鈥渆vil鈥�. But the attackers and their victims were chimpanzees living in Gombe Stream National Park, Tanzania. When primatologist Jane Goodall first reported it in 1975, she called it 鈥渂arbarous murder鈥�. Can a chimpanzee be evil? Or, for that matter, good?

Philosophers have long wrestled with the nature of good and evil. Are they an inseparable duality? Are some things inherently good or evil? These questions seem too abstract to be answered by science. But by asking questions such as 鈥渨hy are animals altruistic?鈥� and 鈥渨hy do chimps sometimes violently kill one another?鈥�, biologists have arrived at an explanation that applies equally well to humans. Underlying good and evil is the neutral hand of natural selection.

鈥淏oth 鈥榚vil鈥� and 鈥榤oral鈥� behaviour could serve one鈥檚 inclusive fitness interests, depending on the individual and the circumstances,鈥� says , an evolutionary biologist at Simon Fraser University in British Columbia, Canada. Inclusive fitness refers to the genes you share with close relatives, which are passed on to their offspring. It is why some animals have evolved to do things like help siblings raise their young. Even though the helper is not raising its own brood, the shared genes benefit. What appears at first to be a selfless act is selfish at the genetic level.

Other things that appear purely altruistic are also better explained by a long-term benefit to the do-gooder. For example, blood donation is often cited as a totally selfless act, but one study found that it is more likely to be an act of self-interest. People who believe in the potential personal benefit of blood banks are than people who think mainly of their benefit to society.

鈥淕ood鈥� behaviour, in other words, is often about personal gain 鈥� which casts something of a shadow on the concept. 鈥淓vil鈥� behaviour might be the same thing. Take those infanticidal chimps. Subsequent observations suggest that such acts occur at times when competition for food and other resources is higher 鈥� so killing the competition means more bounty for your own genes.

Josephine Head, a biologist who witnessed horrific chimp violence in Loango National Park in Gabon, says the behaviour of our closest living relative gives us a window onto the roots of some human violence. 鈥淭he tendency for group violence between males, and the strong 鈥榰s and them鈥� mentality we attach to everything, can be traced back to this adaptive behaviour in apes,鈥� she says.

Extreme behaviour may be influenced by evolution in other ways. Money is sometimes paid to the families of suicide bombers, for example. 鈥淚nclusive fitness effects are likely at work here, though in ways that are evolutionarily novel,鈥� says Crespi.

Of course, as with other kinds of extreme behaviour, there are factors that aren鈥檛 rooted in evolution. Many people who commit horrific acts grew up in abusive or otherwise detrimental environments, which can have neurological, psychological and genetic consequences. And some behaviours are down to random mutations. 鈥淐razy mass killers are likely just that 鈥� insane 鈥� which is maladaptive like any other disease or major disorder,鈥� says Crespi.

鈥淓verything that can happen does happen, only in different universes鈥�

Where does all this leave us with regards to the big question? Good and evil don鈥檛 exist in any real sense. And there is a positive take-home message. The evolutionary pressures that can make humans violent can also make us extremely peaceful, says Martha Robbins, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Our sense of morality can eliminate 鈥� or at least minimise 鈥� evil in society.

This article appeared in print under the headline 鈥淲here do good and evil come from?鈥�