Science: March of the Timewalkers
Gamble, Clive, The Independent (London, England)
IMAGINE a world where humans inhabit just a small corner of a single continent - a fact of geography for most other species. For Homo sapiens, however, the situation is almost unthinkable. One of the distinguishing characteristics of human beings is their global ubiquity, which came about many thousands of years ago. Anthropologists have long argued about how this early migration could have occurred; recent research is beginning to provide the answers. Just as importantly, scientists have begun to form a picture of what drove humans to travel to the four corners of the earth.
The story appears to begin about 1.8 million years ago, in the region of Africa south of the Sahara that is said to be the cradle of humanity, judging from the wealth of ancestral bones that have been found there. It was here that a species of early human lived a simple foraging existence, although its way of life was no doubt considerably more sophisticated than that of any ape-like animal which had lived before.
Homo erectus had a relatively large brain - two-thirds the size of ours - a robustly built body, broad feet, nimble hands and, as the name implies, an upright, two-legged stature. They patrolled large territories in search of food and mates and fashioned simple stone tools; they communicated using gestures, facial expressions, sounds and probably groomed each other to reinforce social bonds. They resembled modern humans enough for the anthropologists who first discovered their fossilised remains to classify them alongside humans rather than apes.
Until very recently one of the great puzzles about H. erectus was why, with all these obvious advantages, the species appeared to have remained in sub-Saharan Africa for as long as 800,000 years? Why, with their brains and clever hands, which could manipulate stone tools, and presumably with a sophisticated social network, did they live only in one place for so long before moving on to populate other parts of the world?
Fossil bones and tools of H. erectus have been found in the Middle East, South-east Asia, China and Europe, so archaeologists have presumed that the species eventually did make its way past the natural barrier of the Sahara desert and over the land bridge between Africa and the Middle East to Asia and Europe. In the past month, however, new dates of a site in Java where H. erectus fossils have been found have suggested that the early hominids may well have migrated much earlier than previously believed - the Java fossils seem to be about 1.8 million years old, making them at least as old as the oldest H. erectus fossils in Africa.
Scientists are now trying to validate these new dates, which appear to make H. erectus a far older traveller than anthropologists previously supposed. This could explain the apparent conundrum of why they stayed so long in Africa - they didn't. Instead of sitting around in their sub-Saharan "home" for nearly a million years, they expanded rapidly. On these timescales, the overland distance of 13,000 kilometres from Nairobi to Jakarta could have been covered very slowly indeed, perhaps less than a kilometre a year, and yet this still seems instantaneous compared to the couple of million years of human evolution.
This new find suggests that H. erectus had all the accoutrements necessary for migration early in their evolution. Since they strode, rather than waddled (like the earlier hominids belonging to the group known as the Australopithecines), they were not limited by locomotion. They were omnivorous and well suited biologically to a range of environments away from the tropics where they were first found. Their large social groups provided defence against carnivores such as lions and hyenas and their survival was helped by primitive technology. The durable stone implements that have been found could well be tools used to make other artefacts from wood, leaves, bamboo and animal tissues. …