- A finger bone from Siberia suggests early humans had yet another close cousin, Ian Sample reports
From nothing more than a piece of bone from a child's little finger, the human family tree has gained another member, one who lived alongside modern humans perhaps as recently as 30,000 years ago.
- Last week's revelation, that scientists in Germany had discovered that the bone recovered from a cave in the mountains of southern Siberia almost certainly belonged to a new species of human; has sent ripples of excitement through academic circles. For the first time, the analysis of ancient DNA has rewritten the human story. Some 30,000 years ago, human life was far richer than we could have imagined.
- Until recently, palaeontologists’ view of human evolution was desperately lacking. Ask them to paint a picture of human existence 40,000 years ago, say, and they would mention modern humans, Homo sapiens, occupying vast territories. The only other hominid in existence back then, Homo neanderthalis, was eking out a life alongside us modern humans, but its populations were in terminal decline. Then the Neanderthals became extinct around 25,000 years ago. That much was agreed upon.
- Things changed in 2003. Field researchers working in caves on the Indonesian island of Flores uncovered remains of a diminutive human relative that lived at least 13,000 years ago. The Flores "hobbits" grew to be a metre tall as adults and could be traced back to Homo erectus, the forerunner of modern humans that left Africa 1.9m years ago. The hobbits' size is thought to be a direct result of their isolation
- Then there is the latest discovery, with which the number of early human species, or hominids, living 30,000 years ago has risen to four. In the space of a decade, the size of the human family has doubled.
- And it's not just the cast list of the human evolution story that has had to be revised. Excavations of fossilised human remains have now led scientists to talk of three great migrations out of Africa. The first footprints leading off the continent were left by Homo erectus. The next migration, around 450,000 years ago, was the Neanderthals. Then, perhaps as recently as 60,000 years ago, the first modern humans left to populate Eurasia and beyond - the humans from whom all of us alive on earth today are descended. The new species of human appears to fit in with none of these migrations out of Africa, and instead points to yet another great exodus, one .that happened around 1m years ago.
- To some scientists, even this fairly complicated picture is beginning to feel oversimplistic. "I don't think we can be absolutely certain about anything now,” says Professor Terry Brown, an expert in ancient DNA at Manchester University.
- What we do know is that the story starts in Africa, but that early humans then decided to leave. "There's no reason why a hominid should remain in Africa if the population increases," says Brown. “The natural thing for it to do is to move." The march out of the cradle of humanity may have been more of an ongoing wander, with early humans moving farther afield as and when they needed.
- What's also known is that, with the exception of the hobbits of Flores, every human species is thought to have evolved before making its way out of Africa. How we ended up with a number of different hominids is probably down to geography: species can split into two when groups of individuals become isolated from one another. When they stop interbreeding, the genetic makeup of each group drifts and diverges. They adapt differently to their habitats. Eventually, the differences became so large they cannot reproduce even if they tried.
- In Africa – a very big place – small groups of thousands likely occupied disparate territories, and many splits may have occurred. Eventually, as the evolutionary clock ticked by, some Homo erectus embarked ona a route that led to modern humans. Still others, scientists now believe, became the new cave species that left its little finger in a Siberian cave.
- The most intriguing thing, perhaps, is its location. The bone was uncovered in an area where the remains of humans and Neanderthals have all been found from around the same period. Together, the evidence points to a time, between 30,000 and 40,000 years ago, when all three species were there. Did they ever meet? Did they fight? And why was <>Homo sapiens the last human standing?
- If they did live alongside one another, they needn’t have been in constant conflict. Conflict is only likely when there is competition for the food, mates or shelter. That said, the tree human species probably all hunted large mammals, including woolly mammoths and woolly rhinos, the remains of which have been unearthed in the area.
- In the next few months, the Leipzig team expects to have sequenced the creature’s full genome, a step that will do more than confirm whether it is a new species. One of the perennial questions in human origins research – and one genetics is uniquely well-placed to answer – is whether co-existing human species mated with each other. Detailed studies of several Neanderthal genomes by the same laboratory have found no compelling evidence that inter-breeding happened between modern humans and Neanderthals. But only further work will rule it out. The discovery of this new human species, one that lived at the same time as modern humans and the Neanderthals, does nothing to make this uncertain picture any dearer. Now there are two human species that died out, if not in our presence, then certainly in our proximity. "That makes the whole argument more interesting and it is going to be the debate that is had over the next 10 years," Brown says.
- The fossil record we have for humans is patchy and incomplete, but tiny fragments that have been labelled, over the course of many decades, as Homo sapiens, or Homo neanderthalis, or Homo erectus, sit in museums and laboratories all over the world.
- Are there fragments of bone from other unknown humans among them? "It could be that there is a whole load of human ancestors out there that we don't know about yet, and I mean five, six, or seven types of human," Brown says. "Everything is wide open now."
See "McKie (Robin) - Out of Africa: The Sequel"
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