Boning up on the truth about our ancestors Once upon a time, two kinds of humans lived alongside each other: our ancestors and their heavy-set cousins, the Neanderthals. We interbred with them. We may have out-competed them, even waged war on them. And eventually, they died out, leaving Homo sapiens in control. About a decade ago, however, we started to realise that the story isn't that simple. On a remote Indonesian island, scientists found the remains of Homo floresiensis, aka the "Hobbit," a completely separate kind of human that, like the Neanderthals, also survived until as recently as 50,000 years ago. And now a remarkable discovery - involving the extraction of DNA from the oldest human bone ever found - has given us even more evidence that human evolution is not a simple stream, flowing from ape to modern human, but a slow-flowing river that has been diverted into countless tributaries. The story starts in the Sima de los Huesos, or "Pit of Bones," a vertical shaft in the Atapuerca cave system of northern Spain. Over the years, this has yielded the world's largest assembly of fossils from the Middle Pleistocene, which lasted from around 800,000 to 126,000 years ago. A team led by Juan Luis Arsuaga, of the Centre for Research on Human Evolution and Behaviour in Madrid, has spent more than two decades piecing together around 28 skeletons of primitive human beings. He classifies the fossils as Homo heidelbergensis, the ancestor of the Neanderthals as well as modern humans - although others, such as Chris Stringer of the Natural History Museum, believe they were actually Neanderthals, or at the very least Neanderthals-in-the-making. That would not be surprising, since it slots into a familiar picture involving the decline and fall of a once-mighty empire. Around 300,000 years ago, the territory of the Neanderthals stretched from Asia to Western Europe, where they hunted with heavy spears in forests and grassland. No one knows for sure what happened when they met our ancestors some 50,000 years ago - except that a few millennia later, the Neanderthals went into drastic decline, disappearing within 20,000 years. Advances in technology, however, have not just filled in the blanks, but redrafted the story completely. Until recently, fossil researchers focused mostly on the shape and nature of the bones they found. But Matthias Meyer, Svante Pääbo and their colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig have now extracted and studied DNA from a femur in the Pit - the oldest yet found from one of humanity's relatives. Two grams of bone were ground into powder, and the genetic information in the mitochondria (the cells" "power packs") extracted. DNA this old is normally retrieved only from permafrost, because it breaks down in warmer climates; luckily, the cool of the Spanish burial site kept it relatively intact. This is where the researchers got a big surprise. As The Daily Telegraph reported yesterday, the Spanish DNA turned out not to be from the Neanderthals or Homo heidelbergensis. Instead, it was related to the Denisovans, enigmatic relatives of the Neanderthals whose remains were discovered in 2008 in a Siberian cave. In that case, studying DNA from a little finger and two molars had shown that they belonged to three individuals, one of whom was a girl with brown eyes, hair and skin who died at least 50,000 years ago. By studying the mutations in the mitochondria - which show how far two individuals are from sharing a common ancestor - the experts have worked out that the Spanish cavemen lived about 400,000 years ago, and shared a common ancestor with the Russians about 300,000 years before that. The only problem is that there is no evidence that the Denisovans got anywhere near Spain. So what's going on? As so often in science, new facts turned a simple story into a more complicated and much more interesting one. We know Neanderthals, Denisovans, and Homo sapiens shared an ancestor, most likely in Africa, about 500,000 years ago. But when was the split between Neanderthals and Denisovans? And are there other unknown tributaries of the human stream waiting to be found, like the hobbits of Indonesia? These questions are not just a matter of history, but biology. For our newfound ability to study DNA from hundreds of thousands of years ago could shed new light on the greatest story of all: which genes, and which ancestors, played a starring role in our evolution into a species that could harness fire, exploit electricity or invent the internet? By shifting our gaze from the shape of our bones to the DNA inside, we're slowly edging closer to learning what it truly means to be human. Roger Highfield is director of external affairs at the Science Museum