I’ve written quite a bit about the Homo floresiensis controversy: these are the small (1-meter tall) individuals whose remains were found in a cave on the Indonesian island of Flores, originally dated about 18,000 years old. They are remarkable because of their size, their small brains (about the size of a chimp’s) and their remarkably recent age — a time when the much taller and brainier Homo sapiens had already infested the world. But there was doubt about whether these diminuitive fossils represented a real species: some people thought that the one relatively complete skull represented a diseased or microcephalic individual.
Two papers in the latest issue of Nature (links below) address this controversy, and both come down on the side of H. floresiensis being a real species, not an aberration. (There’s also a very nice two-page summary by Daniel Lieberman if you don’t want to plow through the articles.) More bones have been found in the Liang Bua cave on Flores (see below), most notably a pretty complete foot. The foot, like the rest of the skeleton, shows an intriguing mixture of primitive and derived traits. There are now enough bones to pretty much rule out the “aberrant individual” theory.
So what was H. floresiensis? As the diagram below shows, it could have been a descendant of an earlier hominin species, H. habilis, or perhaps a very early form of H. erectus; in both cases it would have had to reach the island several million years ago. Yet the brains of these two ancestors were larger than that of the hobbit, so how did it get such a small titer of gray matter? (Hobbit brains were about 400 cc in volume, the size of a modern chimp or of the smallest australopithecines.) Here the notable dwarfism of many species on islands (including elephants on Flores) comes in: like other mammal species, H. floresiensis could simply be an evolutionarily dwarfed form of an earlier hominin. Weston and Lister’s paper gives relevant data taken, oddly enough, from dwarf hippos on Madagascar , but I’ll leave you to follow their reasoning in their article.
This is perhaps the most bizarre and interesting twist in hominin evolution yet, and it’s completely unsettled. A whole new group of questions open up. How did this weird species coexist with the much larger and brainier H. sapiens for so long? (H. floresiensis was not dumb, by the way: they managed to colonize the island over water and made fairly sophisticated tools). If hobbits are a remnant of the H. habilis lineage, how come we don’t find habilis fossils elsewhere outside of Africa?
Ling Bua cave on Flores: where the hobbits were found. Photograph by C. Turney, University of Wollongong
Homo floresiensis might be most closely related to early H. erectus, but also shows potential affinities with H. habilis. In either case, recognizing H. floresiensis as a species will require us to re-examine how we define species of the genus Homo and how they were related to each other. Reasonably well-known relationships are indicated by solid arrows; less secure relationships are indicated by dotted arrows. Broken vertical bars indicate uncertainties about when species evolved or went extinct. (Figure and caption from Lieberman’s summary.)