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 “why are animals altruistic?” and “why do chimps sometimes violently kill one another?”, biologists have arrived at an explanation that applies equally well to humans. They suggest that underlying good and evil is the neutral hand of natural selection.

Scientists think that both ‘evil’ and ‘moral’ behaviour have two evolutionary roots.  One relates to the genes you share with close relatives, which are passed on to offspring and which influence you to, for instance, help with the rearing of children and do things for the extended family. Even though you are not raising your own brood, the shared genes benefit. What appears at first to be a selfless act is selfish at the genetic level.

The second influence is best explained by long-term benefits to the do-gooder. For example, blood donation is often cited as a 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 more likely to donate than people who think mainly of their benefit to society.  “Good” behaviour, in other words, is often influenced by personal gain. “Evil” behaviour might be the other side of the equation.  Take infanticidal chimps. Subsequent observations suggest that when chimps kill the young they do so at times when competition for food and other resources is high, so killing the competition represents an advantage for the killer.

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. “The tendency for group violence between males, and the strong ‘us and them’ mentality we attach to everything, can be traced back to this adaptive behaviour in apes,” she says.

But there are also factors that are not rooted in evolution. Many people who commit horrific acts grew up in abusive or violent environments, which can have neurological, psychological and genetic consequences. And some behaviours are down to random mutations. “Crazy mass killers are likely just that – insane.

So those who study these things think that good and evil don’t exist in any real sense. But they do agree that the evolutionary pressures that can make humans violent can also make us extremely peaceful. Our sense of morality can eliminate – or at least minimise – evil in society. (A precis of an article by Rowan Hooper, New Scientist)

My personal opinion is that we are blessed with some measure of common sense and self-interest. If one treats people in thoughtful, kindly ways, ask them about themseves, offer little kindnesses and take an interest in them and what they think, then you will be rewarded accordingly. Put it another way: behave in a rude, uncaring, humourless way and you will soon have no friends. It isn’t rocket science.