The skull of Homo floresiensis is tiny compared to modern day Homo sapiens.© P. Brown

The conventional view of early human evolution is that the species Homo erectus was our first relative to spread out of Africa, some 2 million years ago. The spread that our cousin achieved is indicated by a 1.8-million-year-old, primitive form of H. erectus found at Dmanisi in Georgia, and by finds at slightly younger sites in China and the Indonesian island of Java. It was not thought that H. erectus travelled any farther towards Australia than this, because although early humans could have walked to Java from Southeast Asia at times of low sea level, the islands east of Java, always separated from it by deep water, seemed beyond their reach.

However, six years ago a team of archaeologists, led by Australian Mike Morwood, published a paper claiming that a site on the island of Flores, 500 kilometres east of Java, contained stone tools dating from about 800,000 years ago¹. Many researchers (myself included) doubted these claims, because if they were true they implied that H. erectus had moved beyond Java and might have used boats to do so. Such a development was thought to be unique to Homo sapiens.

When I then heard rumours about the discovery of an early human skeleton in a cave on Flores, I was ready to be surprised. However, nothing could have prepared me for how big (or small) that surprise would be.

Asian fusion

The skeleton found at Liang Bua, a cave on Flores, is of an adult who was only about one metre tall with a brain size of only 380 cubic centimetres. That is less than one-third of the average brain size for a modern human and much smaller even than those of the primitive H. erectus skulls from Dmanisi.

The Flores skull shows a unique mixture of primitive and advanced characteristics. The brain is the same size as a chimpanzee's, the brain-case is low with a prominent brow ridge at the front, and the lower jaw completely lacks a chin. However, as in modern humans, the face is small and delicate. It is tucked under the brain rather than thrust out in front and the teeth are similar in size to our own.

The skeleton shows a similarly strange mixture of features. The hip-bone resembles those of the pre-human African species known as australopithecines (meaning 'southern apes'). But the legs are slight, and enough detail has been preserved to show that this creature definitely walked on two legs, as we do.

Class act

This skull almost certainly belonged to a woman, who lived 18,000 years ago.© P. Brown

So what was this strange creature, and what was it doing on Flores? The authors of the two Nature papers²,³ about the discovery and its context have had to make difficult choices in deciding how to classify the creature, although it is clear that this person was definitely not a modern human. The small brain size and the hip-bone shape might favour classification as an australopithecine, whereas the size and shape of the skull might suggest a primitive form of H. erectus.

Given the unique combination of features, the authors have decided to give the specimen a new name: Homo floresiensis. This means, literally, 'man of Flores', although the authors recognize that the Liang Bua skeleton is probably that of a woman.

The researchers argue that this species made the tools found in the Liang Bua cave, and may have preyed on one of the few other mammals that had also managed to reach Flores: a tiny form of the extinct, elephant-like Stegodon.

Of a certain age

It seems that Flores man (or woman) still has one more surprise up its sleeve: its age. Astonishingly, two methods of dating agree in placing the skeleton at only about 18,000 years old. Its ancestors, probably a form of H. erectus, could have reached the island in the hunt for stegodons a million years ago, either by building some kind of boat or by walking across a short-lived land-bridge.

Their resulting isolation and inbreeding may have led them to evolve a small body size, in a process known from other mammals as 'island dwarfing'. Because of climate change or the impact of modern humans, who began to spread from Africa around 100,000 years ago, the strange story of H. floresiensis eventually ended in extinction. But modern humans must surely have encountered this tiny relative of ours, and the discovery shows how much we still have to learn about the story of human evolution.

Chris Stringer is a palaeontologist at the Natural History Museum in London.  

• References

  1. Morwood M. J., et al. Nature, 392. 173 - 176 (1998). | Article | ISI | ChemPort |
  2. Brown P., et al. Nature, 431. 1055 - 1061 (2004). | Article | PubMed | ISI | ChemPort |
  3. Morwood M. J., et al. Nature, 431. 1087 - 1091(2004). | Article | PubMed | ISI | ChemPort |