We came within a whisker of having to share this planet with another, but very different, human species. Just 18,000 years ago, when modern humans were beginning to farm the fertile crescent, another human-like population was hunting dwarf elephants in the jungles of Indonesia, asks Dick Ahlstrom
The scientific world was stunned last week with the announcement of the discovery of a completely new species of early human. Dug out of a cave on the Indonesian island of Flores, the new creature Homo floresiensis has forced a rethink of our understanding of human evolution.
It had a brain smaller than a chimpanzee but made extensive use of tools and was able to use fire to cook its food. It measured no more than one metre in height but managed to survive for thousands of years sharing space on Flores with Komodo Dragons and another even larger carnivorous lizard.
Details of the excavations at Flores were described last week in the science journal Nature. A near complete skeleton from one individual was found along with bone fragments from another six. All came from Liang Bua, a large limestone cave that has been the site of digs for almost 40 years.
The work provides evidence that these small creatures lived on Flores from perhaps 95,000 years ago until at least 18,000 years ago. The research team, led by scientists from Indonesia and Australia, suggests that the population could have been wiped out by substantial volcanic eruptions in the region 12,000 years ago, or perhaps by changes in climate as the last ice age came to an end.
The most striking feature of the discovery is how recently the creatures co-existed with our own ancestors, Homo sapiens, says Prof Dan Bradley, a specialist in genetic anthropology in Trinity College Dublin's genetics department.
"The real thing is their age," he says. "They lived only 12,000 years ago at a time when our ancestors were starting to herd goats and live like we do today. At that time these folks were around," he notes.
"Twelve thousand years is the blink of an eye in the history of a species. This means we just missed out on having surviving cousins on the planet. They almost made it to the present day."
The accepted wisdom until now was that only two species of early humans lived in Asia during that period, Homo erectus and Homo sapiens. Both had large brains, walked upright, and had larger bodies and smaller teeth than the more ape-like earlier human ancestors.
Homo floresiensis put a dainty foot through that theory with the Flores dig and the September 2003 unearthing. The excavations showed that it competed successfully and survived over a long period in the region.
The near complete skeleton, dubbed LB1, measured about one metre tall. Analysis of the bones suggested it was an adult female, perhaps 30 years old at death, and its teeth showed considerable signs of wear. It would have weighed between 16 and 29 kilos.
The initial problem for the scientists was where to put it on the human family tree. It was shorter and had a smaller brain than very early African ancestors such as Australopithecus afarensis, a famous example being the more than three million-year-old skeleton "Lucy". The authors acknowledged that Homo floresiensis, with a brain volume of just 380 cubic centimetres, was "well below the previously accepted range for the genus Homo".
Yet LB1 also displayed modern human characteristics. Its face was much more like other Homo species, the report points out. It doesn't carry the heavy jaw and large teeth of an Australopithecus. Its face and jaws were "most similar in relative size and function to modern humans," it says, hence their inclusion of LB1 in the Homo genus.
The researchers also believe they can explain the creature's small stature. Modern African pygmies are small because of reduced levels of certain growth factors but the scientists doubt the same applied to Homo floresiensis.
Rather, they attribute its size to "insular dwarfing", a well-recognised evolutionary mechanism that produces either very small or very large organisms as a result of isolation within an island population.
A poor low-calorie diet and a lack of predation combined so that "environmental conditions placed small body size at a selective advantage", the authors of the report state.
They believe early populations of Homo erectus may have reached Flores only to become dwarfed after thousands of years. Something similar happened to Homo floresiensis' main prey, primitive pygmy elephants known as stegodons.