It might sound to you like a dumb thing to say, but when I finally got my head round the origins of our species, the story made me cry. It was a Sunday morning at the time, and I was chasing the subject on Tanzania's Serengeti Plain in a rented Hyundai four-by-four. Clouds of ochre dust boiled behind the vehicle. Zebra and gazelle leapt up left and right. And a compass needle bounced on the passenger seat beside me as I sped across the roadless terrain. There was no other person as far as the horizons: if the car broke down I might have starved. And then weeks of research fused together with the landscape, bringing tears to my sunglazed eyes.
The funny thing was that before I checked it out, I had assumed all that corny "Garden of Eden" stuff was on videotape, in the can, cut and dried, decided. After all, who can't recall some celebrity anthropologist strolling towards a television camera, holding forth about how Homo sapiens sprang from Homo erectus, which, in turn, was begat by Australopithecus, which, a very, very, very long time ago hung around in the trees like apes? It has been 6 million years since we split from the chimps. Your first thought isn't breaking news.
All the punditry I'd seen on the subject, moreover, was no reason to act like a wimp. By most accounts, humanity's triumph over the animal kingdom was a spiteful business, as Charles Darwin's principle of natural selection was played out between competing bands of proto-humans, or hominids, in old world locations such as this. Even schoolkids know how our descent from the trees marked the start of our use of tools and weapons - and how the most ruthless hunters and killers amongst us proved the fittest and therefore survived.
This account is mostly the legacy of the science of palaeontology - the finding and making sense of fossils. For the best part of the twentieth century, a steady accumulation of fossilised hominid fragments have been indexed and displayed in museums around the world, like keyholes to peer into Eden. And with little else apparently surviving decay and the crushing weight of millions of years of rock-forming debris, they have taken centre stage in our picture of human origins, helping to shape our image of ourselves.
To date, East Africa has provided most of the key specimens - with the most celebrated site for headline-grabbing finds not far from my route that Sunday. The parched Olduvai Gorge, the so-called "Grand Canyon of evolution", and since the 1930s location of world-famous bone hunts by the white Kenyan adventurers Louis and Mary Leakey, was just 40km south-east of my route, back towards the Ngorongoro Crater. I had spent a bit of time there, among wind-eroded sediments, where for decades they had scoured the ground.
The Leakey's fingers are all over palaeontology. It's impossible to discuss it and miss them. Deploying vast grants from the National Geographic Society in Washington, and boosted by countless National Geographic magazine stories, Louis and Mary Leakey, their son Richard, his wife Meave and their daughter Louise, acquired what amounted to an exclusive franchise over east African fossil sites. For the past half century, squads of sharp-eyed local workers have tramped thousands of square miles under their imperious direction, to supply a stream of celebrated skull and bone fragments for the society to photograph and film.
It was a guy called Dr Raymond Dart, however, who was the father of this line of inquiry. Before World War II, as a professor of anatomy at South Africa's Witwatersrand University, he became renown for bringing to the public's attention a string of 3m-year-old Australopithecus finds - a so-called "missing link" genus he named (It's Latin for "southern ape"). And it was he who forged the now-commonplace assumption that the reason why we evolved from our tree-swinging cousins was our forebears' relentless violence.
He first staked this claim in 1953 in a paper titled The Predatory Transition from Ape to Man which, although read by only a few specialists, did nothing less than to trigger a science-based movement turn the century's intellectual tide. Published in the obscure Miami-based International Anthropological and Linguistic Review (whose editor sheepishly claimed that Dart was referring only to "the ancestors of the modern Bushman and Negro, and of nobody else"), in 1961 his ideas reached the public via a Chicago scriptwriter, Robert Ardrey, who turned Dart's conjectures into a 350-page best-seller, catchily titled African Genesis. As I sped across the Serengeti that Sunday morning, it lay caked in dust under my compass.
"What Dart put forward," Ardrey explained, "was the simple thesis that Man had emerged from the anthropoid background for one reason only: because he was a killer. Long ago, perhaps many millions of years ago, a line of killer apes branched off from the non-aggressive primate background. For reasons of environmental necessity, the line adopted the predatory way. For reasons of predatory necessity, the line advanced. We learned to stand erect in the first place as a necessity of the hunting life. We learned to run in our pursuit of game across the yellowing African savannah."
This powerful notion was soon grabbed by popular zoology when in 1967 a London Zoo curator and children's television presenter, Desmond Morris, broadened its appeal in another best-seller, Naked Ape, reprinted a dozen times in 18 months. And then, in the ideologically pivotal year 1968, Dart's thinking reached a truly mass audience in the opening sequence of Stanley Kubrick's 2001: A Space Odyssey, listed by Variety magazine as one of the top 50 moneymaking movies ever.
I remember my father taking me to see a rerun - and Hal, the computer, left barely a trace on me compared with that sequence projected in the dark. Under eerie red skies on a barren landscape, and following a brave caption THE DAWN OF MAN, a bunch of guys in gorilla suits hop about grunting, and foraging for berries and roots. But then one grabs a zebra femur and (to the majestic swell of Richard Strauss's Thus Spake Zarathustra) begins pulverising stuff in slo-mo swings, with a crazy kind of stare its eyes.
Before this multimedia blitz for Dart's hypothesis, science-based debates on the origin of our species had been short of an epic narration. While evolutionary theory back to Darwin suggested that we must have shared ancestors with our three fellow ape survivors - the chimpanzee, gorilla and orangutan - there was no convincing, much less agreed, hypothesis as to why this should have occurred. The complexity and apparent purposefulness of human tissues, nerves, muscles and so on seemed to many improbable features to be merely the products of random mutations.
In what Ardrey dubbed "The New Enlightenment", it was Dart who stepped into the post-Darwin void to displace the hand of god. "Australopithecus lived a grim life," the anatomy professor wrote, graphically sketching his portrait of Adam and Eve. "He ruthlessly killed fellow australopithecines and fed upon them as he would any other beast, young or old. He was a flesh eater and as such had to seize his food when he could and protect it night and day from other carnivorous marauders."
In the late 1960s, as the liberal civil rights, antinuclear and Vietnam War movements, reached a crescendo, conservative ideologists seized on this hypothesis, which seemed to point in a welcome direction. Just as Siegmund Freud had stirred resonances in the century's first half by revealing the child who lives within us, so the "killer ape" hypothesis beckoned in the second half, suggesting that such a child, if it survived at all, rode on a wild animal's back.
What clearer precedent for, say, the manifest destiny of white men to rule, or the unfairnesses of the free market, than a scientifically-proven and commercially-successful theory that predatory aggression was no mere vice, but the driving force of who we are? "Far from the truth lay the antique assumption that man had fathered the weapon," wrote Ardrey in full-blooded scriptwriter mode. "The weapon, instead, had fathered man."
That it's a cruel world, after all, didn't you know, is a lesson from our relatives in the wild? Even before Dart's message became entrenched as orthodoxy, Louis Leakey had in 1957 installed Jane Goodall, a 23-year-old secretary from England, to report on the common chimpanzee population at Gombe River - maybe a day's drive to my south-west, near Lake Tanganyika. In what was considered science for the period, the former waitress had arrived at Gombe, ordered the grass cut and dumped vast quantities of trucked-in bananas, before documenting a fractious pandemonium of the apes. Soon she was writing about vicious hunting parties in which our cheery cousins trapped colubus monkeys and ripped them to bits, just for fun.
Dart, the Leakeys, Goodall - the lot of them - had, of course. studied their specialities for decades. I, meanwhile, was merely passing through, little more than a Sunday afternoon driver. But as the zebra and gazelle scattered around me that morning, I reconnected with a feeling that I had been getting for some time: that the killer ape story was fiction. Like with the guy who more recently wrote a book called The End of History, claiming that human organisation had achieved its ultimate manifestation (in American capitalism), it was a mixture of wishful thinking and catchy formatting, primarily intended to sell.
I had felt something was amiss even before arriving in Africa, but after talking with a new generation of scientists from the United States, Europe and Australia, and mugging-up on shelvesful of the latest research in the library at Kenya's national museum in Nairobi, I had found new evidence, refuting Dart's narrative. And as I had travelled around the Great Rift Valley of east Africa, looking at sites where research was happening today, it seemed to me that his tale was little more than a thriller - understandably attracting scriptwriters and directors.
In a sense, you can disprove Dart by looking into yourself. But new, more objective, methods have emerged to reanalyse the hard surviving evidence of our past. With Dart and Ardrey long-dead, the Leakey dynasty losing influence over the African sites, and even Hyundai four-by-fours available for hire, archaeologists, geologists, climatologists, botanists, geneticists and all kinds of scientists, using revolutionary investigational methods, are breaking into the domains of the old white adventurers. And they are finding new keys to Eden.