Inside view of our wee, ancient cousins.

A half-size Homo species that lived on an Indonesian island more than 20,000 years ago possessed a remarkably small yet capable brain. According to a new report, that brain shows organizational similarities to the larger brain of Homo erectus, a human ancestor capable of complex thinking.

Dean Falk of Florida State University in Tallahassee, working with the Australian researchers who discovered the diminutive Homo floresiensis fossils (SN: 10/30/04, p. 275), took computed tomography scans of the braincase of a female skull from the island site. The researchers used those data to construct a three-dimensional surface portrait of the prehistoric individual's brain, including such details as tissue folds and blood vessels.

The scientists compared that virtual brain with portraits generated from six H. erectus skulls dating to more than 200,000 years ago, two skulls of human ancestors that lived nearly 3 million years ago, 10 modern human skulls, to gorilla skulls, 19 chimpanzee skulls, a skull from an adult African pygmy, and a skull from an adult whose brain was abnormally small because of a genetic disorder.

The upshot, the researchers report in an upcoming Science, is that H. floresiensis exhibits a unique pattern of brain organization and so should be considered a separate species. Like H. erectus brains, the H. floresiensis brain had unusually large tissue expanses near its front and midpoint, relative to overall brain size. The two species thus may have been closely related, Falk's group suggests. H. floresiensis may even have evolved from a larger to a smaller size while living on the Indonesian island near H. erectus groups, the investigators say.--B.B.