BRIAN DEER: NATURE'S PREY Page 4

Beside the few dusty tracks that today cross the Serengeti, you will sometimes see a hyena or two panting in the heat. If you want, you can get out and pet them like house-dogs. And they would happily rip you to shreds. Best stay behind safety glass to coexist with wild animals. Thank god for the automobile.

But now try to think about Homo erectus, plodding across the plain in bare feet. Around 2 million years ago was the period of maximum evolutionary diversity, and while today we have cause to fear the pack-hunting hyena, back then there were at least six species. While east Africa today boasts the serious presence of three big cats - the cheetah, leopard and lion - back then there were ten, some much bigger and uglier than anything a zoo could contain. While the lakes today may boast 16ft Nile Crocodiles, then there were at least four kinds to drag you under, some of them twice the size.

Against such perils, hominids stood little chance once they ventured from the trees' protection. Little chance, that is, until what many scientists believe may have been the real spur to humanity's leap forward. Far from the weapon, or even the tool, being the defining moment, if any one thing marked Dart's "transition from Ape to Man", it wasn't predatory aggression, but the first technology - our ancestors' control of fire.

The champion of this view is the archaeologist Jack Harris, chair of the Rutgers University's anthropology department, who has worked at sites throughout east Africa, including Laetoli, where Mary Leakey famously found hominid footprints. "I have argued that the earliest human-controlled fire was not related to cooking, but for protecting hominids and for securing a place on the ground," he told me. "Prior to that, hominids spent a lot of time - certainly sleeping - in the trees. Once they had fire, they could ward off predators such as lions and leopards. It also allowed them to move into new habitats in the more open parts of the landscape."

Controversially, Harris dates this to 1.6m years ago, much further back than previously believed. Since the 1970s, possible evidence has been collected from a dozen sites, from caves at Swartkrans in southern Africa to the desert of Middle Awash in Ethiopia. But until now all observations have roundly been rubbished by champions of the killer ape. They say that, until the time of the rise of Homo sapiens, our brutish forebears were too dumb and clumsy to accomplish such a complicated feat.

The site deemed proof of Harris's theory is at Koobi Fora, near Lake Turkana in northern Kenya. On what is now a bleak ridge of eroding sediments 20km from the water, surrounded by a volcanic wilderness, materials from a spot hurried over by the Leakeys more than 20 years ago have been subjected to magnetic mineralogy tests which seem to point to an ancient campfire. Stone implement finds and landscape surveys have shown that this was once a living place for hominids, beside a river lined with acacia.

Controlling fire was a revolution: at last there was safety on the ground. Its warmth allowed rapid migration northwards and to higher altitudes. It provided light, thus extending the day. And as a focal point for sharing information, such as where berries or nuts had been found, it was also a spur to developing language - then still only squeaks, clicks and grunts. For the lucky line who got the hang of it first, these features of fire would have triggered a massive brain-boost over those left out in the cold.

"It is probably in this context that people started to talk about the day's activities," Harris said of what he believes to be humanity's most transforming breakthrough. "And it changed the biological clock of humans. Prior to that, humans were like other animals, they were restricted by the daylight hours - particularly humans, who have developed no special adaptation to seeing at night."

Fire, of course, might attract other hominids, but this might not have been a problem. The revisions that the new investigations are bringing about suggest that strangers would more likely have sparked curiosity and desire than any so-called killer instinct. The latest research shows that the gene-swapping breeding stock that led to modern humans never fell below several thousand individuals: meaning that encounters between different groups must have been enjoyed, as they are among other primate species, as opportunities to exchange DNA.

To the chagrin of the pundits of the 1960s, the same picture is now emerging from our cousins in the wild. Despite reports since Goodall's stressing the common chimp's occasional aggressiveness - including a BBC series this summer dutifully dubbing it, as ever, "Man's closest relative" - zoologists now believe that it is the bonobo, the misnamed "pygmy" chimpanzee, which has remained more like the original stock from which Australopithecus - and we - evolved. Only about 15,000 of these animals remain, mostly deep in the jungle of Zaire.

Although the bonobo's DNA shows the same differences from humans as the common chimps's, and it is often of a similar size (but with longer limbs and a narrower chest), the bonobo has rarely been deemed worthy of the discomfort of keeping a watch on its life. But work by feisty Japanese scientists has begun to reveal that, far from it being spiteful or brutish, it enjoys a tranquil life: concluding even the most mundane interactions with indiscriminate collective sex.

"Though there was a clear boundary between individuals of the different groups and they were exchanging loud calls, face to face, no battle was seen," the Japanese team reported (with appropriate breathlessness) in Primatology Today, after spending months waiting for two bands, each of about three dozen bonobo, to meet for the very first time. "After about half an hour, a female of P group approached a female of E1 group and they performed genito-genital rubbing. Then both groups had a peaceful feeding and resting time."

Far from the pulverising violence with which Kubrick's 2001 thrilled the modern public, the accumulating evidence about our ancestors' behaviour is that the worst hominids were most likely to do was cuddle their rivals too hard.

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