Branches appearing on human family tree

When researches unveiled evidence of an extinct race of dwarf humans on a remote island in the Indonesian archipelago last week, the news bordered on fantasy - even to anthropologists.

It wasn't just the fact that this island seemed to be Middle Earth in miniature, with its hobbit-size humans. It was also the fact that no more than 18,000 years ago - a holiday weekend, by anthropological reckoning - we were not the only humans on the planet.

For decades, many anthropologists have posited that humans must have evolved like all other animals - in evolutionary trials and failures. Just because there is only one species of human today - homo sapiens - doesn't mean that there weren't several living together in the past, they say.

Now, researchers are increasingly finding fossils that support that idea. Moreover, this finding and a handful of others suggest that diversity existed across the entire arc of human history - from millions of years ago until almost the present day.

"The increased rate of discovery of fossils has shown diversity," says William Kimbel of the Institute of Human Origins at Arizona State University in Tempe.

Three years ago, Maeve Leakey found a hominid fossil from the same epoch as the legendary "Lucy," pointing to a diversity of hominids 3.5 million years ago. Two years ago, the unexpected features of another find in Chad at least hinted at a diversity of hominids as many as 7 million years ago, though it remains the subject of debate.

The fossils are physical markers of an idea established in the 1970s and increasingly accepted. Before then, most anthropologists believed that the human family tree was a single trunk from the primitive to the present, and every species of hominid could fit consecutively into this one human lineage. In the 1970s, however, researchers found almost certain evidence of two concurrent hominid species. All of a sudden, the tree had at least one branch. Since that day, perhaps the greatest debate in the study of human origins has been this: How many branches are there and when did they split?

Last week's extraordinary announcement has become another battle point.

Since the days of Darwin, islands have always been evolutionists' perfect natural laboratory, allowing plants and animals the isolation to grow in unique ways. One well-known trait of island evolution is dwarfism: Things larger than a rabbit tend to grow smaller than normal, and things smaller than a rabbit tend to become giant. The trend was already well established on the Indonesian island of Flores, where fossils indicate that huge rats and monstrous lizards lived alongside pygmy elephants.

But as more advanced creatures, humans were surely immune to this sort of thing, scientists thought. "This shows that humans - even with culture - are not immune to the same selective pressures on other species," says Daniel Lieberman, an anthropologist at Harvard University in Cambridge, Mass.

Indeed, these dwarf humans, named Homo floresiensis, had stone tools appeared to use fire for cooking. Says Tim White, an anthropologist at the University of California in Berkeley: "This is going to become a classic example of human evolution."

To some anthropologists, evolution teaches one clear lesson: It is a process of fits and starts that spawns many species before one emerges. That makes Flores man exemplary of human diversity.

"It reinforces the perception that our history is one of diversity and experimentation, not one of linear perfection," says Ian Tattersall of the American Museum of Natural History in New York.

To skeptics, though, Flores man merely proves that there was a peculiar species of human that developed at the fringe of modern humans' inexorable rise across Africa, Europe, and Asia. This and other findings do not indicate that several species of humans were competing on equal footing either in the recent or distant past. "Is it possible that there will be five, six ... 10 species of human?" says Dr. White. "It's possible ... [but] as a paleoanthropologist, you have to go with the evidence you have."

Increasingly, though, many anthropologists are saying that new fossils support diversity. Says Dr. Kimbel, "We had all accepted the notion that 30,000 years ago, modern humans were essentially it."