We are not alone in our capacity to kill and rape our own kind, a new study of primates suggests. But is this innate or acquired? And what have we to learn from the bonobos, which prefer grazing, grooming and sex? By Jerome Burne
Every night, our televisions show us evidence of the violence and cruelty being perpetrated somewhere in the world. Perhaps the most shocking incidents are those involving friends and neighbours who live together for years, then suddenly turn on each other with frightful savagery. Here is a description of one incident that followed the splitting of a community:

"Sniff, who as a youngster had played with the Kasekela males, was caught late on 11 Nov. Six of them screamed in excitement as they found him alone. One hit him repeatedly on the nose, another punched him and a third grabbed him by the neck and drank the blood streaming down his face. By the time they left him he was wounded in the mouth, forehead, nose and back. One leg was broken."

In this instance, the community that had divided was not in Bosnia, Chechnya or Rwanda, nor was it composed of men and women: it was a troop of chimpanzees that split in two in 1970. Over the next seven years young males from the larger group regularly went on raiding parties into the territory of their one-time companions. Whenever they found a single male they would excitedly batter him to death; they raped the females and took them back home with them.

This story, which has an awful familiarity about it, is told in the book Demonic Males, by Richard Wrangham and Dale Peterson, which attempts to construct a new understanding of the deep roots of human violence. The conventional view is that humans are unique in their capacity and readiness to kill their own kind, and that the cause lies in our culture and upbringing. In 1987, for instance, UNESCO released a statement on violence written by 20 distinguished scientists which declared that warfare was a "particularly human phenomenon that does not occur in other animals ... it is a product of culture with only a minor biological connection".

The data that has been coming out of field studies suggests otherwise. The commonly held picture of our primate cousins enjoying an idyllic life travelling through the forest, snacking on fruits, spending hours grooming one another is in large part true, but there is a darker side to it. The males of the three species closest to us - gorillas, chimpanzees and orang- utans - are all, in the terms of Wrangham and Peterson's book, "demonic": they batter their females, rape them, kill babies and kill stray males they find in neighbouring territories.

So do we mutter "original sin" and conclude that there is no hope for us? Violence is imprinted in our genes, men are irredeemable shits and any strategy to combat this is doomed to fail? Not at all. For all the "nature red in tooth and claw" that the book reveals, its message is ultimately a hopeful one. To begin with, it establishes very clearly that this violence is never "mindless"; instead it is strategic, carried out when circumstances mean that it yields benefits.

Different circumstances call for different sorts of demonic behaviour, or, in one case, none at all. Among orang-utans, for instance, rape is common but raiding and killing babies isn't. Gorillas, on the other hand, are models of peacefulness with no rape or female battering, but lurking round every male with a harem are single males ready to overthrow the silverback, kill his offspring and mate with the females who will need no coercing. Most violent are the chimpanzees. All the females get battered and raiding parties are brutal, but rape isn't that common and infanticide is rare.

Explaining exactly why these different patterns have emerged can get quite complicated but one key factor is the food supply, which in turn affects the sort of social groupings that are formed, which then determines the violent strategy that offers the best pay-off. Chimpanzees, for example, eat fruit, nuts and meat - food that is sometimes plentiful and sometimes in short supply, unlike the leaves and shoots that are generally available all year round which make up the gorilla diet.

The result is that chimpanzees stay together in groups when food is easily available but split up when it is scarce. They don't form harems like the gorillas but the males fight for food and access to females when they come on heat. Being a more violent chimpanzee pays off because you get more food and more mating and so more offspring. Killing infants, on the other hand, is not worth it because the females mate with many males and almost any child could be yours. The violence is also pragmatic in that it is most common when attackers have the least chance of being hurt themselves. So chimp females are battered because they don't have alliances with other females or males to protect them; chimp raiding parties only attack when they heavily outnumber their victims; challenges to rival males in the group are always done by forming an alliance - two males will gang up on a higher-ranking male and overthrow him in a surprise and savage assault.

The calculated nature of violence becomes very clear with the bonobos - primates found in Zaire which split off from the chimpanzees about 1.5 million years ago, just about the time Homo erectus appeared. They are the silver lining in this cloud of demonic violence. If you are looking for a prelapsarian lifestyle, they don't come much more Garden of Eden than the bonobos.

No rape, no battered females, no infanticide, no murderous raiding parties; just small troops of 16 or so moving slowly through the great forest eating fruit and leaves, grooming each other and having sex, lots of sex. Adults with infants, males with males, females with females, males with females, oral, manual and face-to-face penetrative. Some individuals have been observed having it 12 times a day.

What makes them so different? The most obvious factor is that each troop is ruled by an alliance of females. Among the bonobos it's the females who bond into groups, but unlike the highly competitive chimpanzee male groups who are constantly forming and breaking alliances to get to the top, the female groups support each other. One way they do this is to come down very heavily on any males who start showing any inclination to rape or battery.

Food supply seems to be behind this set-up as well. Although bonobos and chimps live on opposite sides of the Zaire river, with identical flora and fauna, there is one big difference - they don't share the territory with gorillas. This means that the gorilla's main source of food - leaves and shoots - are there for the taking. This in turn means that they don't have to split up when fruit and nuts are in short supply so the troops stay together, giving the females time to form alliances.

Of course it could be argued that all of this is of limited relevance to humans. We have culture and language and our famous big, rational brains. On the other hand there is something instantly recognisable about those competing violent male chimpanzees, bonding in groups and going on their raids.

Take the Yanomamo, a cultural group of about 20,000 who live in southern Venezuela and are the largest tribe in the world that hasn't been pacified, destroyed or westernised. They are subsistence farmers who live in villages of about 90 people and need to work on their plots for only around 3 hours a day for food. They devote most of their remaining energy to raiding their neighbours, killing any solitary males they can find, raping and carrying off any women. The most successful killers have 2.5 times the number of wives the more peaceful males do. Violence pays.

The implication of this new perspective is that we human males - and it does seem to be the males - have the genes for all those demonic forms of behaviour zipped into our own DNA. But female patterns of solidarity and co-operation are there, too. The challenge is to find the social arrangements that make violence not worth the candlen

'Demonic Males', by Richard Wrangham and Dale Peterson, is published by Bloomsbury, price pounds 16.99