FROM CHARLES Darwin's journeys to the Galapagos Islands until now, islands have been the petri dishes of evolution. When species are marooned within the confines of an ocean outpost, their generations' responses to a limited observable environment make them an open book for scientists.
A new, extraordinary chapter in the book of evolution was published last month. Scientists reported in the journal Nature on the discovery on an Indonesian island of the remains from a cousin species of homo sapiens. Just 3 feet tall and with skulls the size of a grapefruit, these humans could use tools, ignite fires, and hunt animals, including a similarly downsized predecessor of modern elephants.
They survived until at least as recently as 13,000 years ago, which means that for thousands of years they were sharing their island, Flores, with modern human beings. There is no record of any contact between the two species, although there are stories that when Dutch sailors first came to Flores in the 16th century they heard tales of "little people" living in the island's caves.
Both Flores man, or homo floresiensis, and the small elephants are textbook examples of a phenomenon that naturalists call the island rule. With few if any predators but with the limited food sources of an island (Flores man seems never to have learned to farm), small becomes beautiful in natural selection. Scientists have also found traces of small elephants like those of Flores on the Mediterranean islands of Malta and Sicily. But this is the first example of any human -- or any primate -- evolving to a dwarf size on an island.
Scientists surmise that representatives of the species first came to Flores on rafts, intentionally or accidentally, at least 840,000 years ago. Flores lies to the east of the Wallace Line, which divides islands in that part of the world. Those to the west of the line were once connected to Asia or Australia and have many mainland plant and animal species, and those to the east, like Flores, have been surrounded by water for the last 2.6 million years and have fewer species.
Scientists are fascinated by the fact that Flores man's brain evolved, with the rest of his body, to a size smaller than a chimpanzee's. But the species was still able to survive as long as it did until, apparently, it was wiped out by a volcano.
The authors of the Nature article note dryly that their discovery shows that "the genus Homo is morphologically more varied and flexible in its adaptive responses than previously thought." Still, if human beings overpopulate this big island known as earth or so poison its soil that agriculture becomes impossible, it is not advisable to count on being able to shrink down over thousands of years to a more manageable size.