Little Ancestor, Big Debate: Tiny islanders’ identity sparks dispute

New measurements bolster the 2-year-old claim that fossils of a half-size human ancestor found on the Indonesian island of Flores represent a new species, Homo floresiensis.

Comparisons of a partial Flores skeleton with bones of other human ancestors and modern people weaken recent arguments that that the island finds come either from Stone Age pygmies or from another Homo sapiens specimen with a genetic condition known as microcephaly that hinders brain growth, concludes a team led by Debbie Argue of the Australian National University in Canberra. A separate group of researchers originally found the fossils.

Argue’s group compared measurements of the Flores fossils—which range in age from roughly 12,000 to 90,000 years—with corresponding data on skull and limb bones from two people with microcephaly who died around 2,000 years ago; a roughly 4-1/2-foot-tall person previously excavated at a 3,000-to-5,000-year-old Flores site; more than a dozen human ancestors ranging in age from 1 million to 3.2 million years; and 584 modern humans, including members of especially short populations.

After considering these comparisons, Argue finds it “unlikely” that the Flores individual was a human with microcephaly or a member of any known species of human ancestors. The Flores skull displays notable anatomical differences from a pair of human skulls—one unearthed in Greece and the other in Japan—that exhibit microcephaly, the researchers say.

The new study will appear in the October Journal of Human Evolution.

Curiously, the Flores specimen’s relatively short limbs resemble those of a 2.5-million-year-old human ancestor, Australopithecus garhi, the team contends. The island species’ skull recalls the shape of nearly 2-million-year-old Homo finds.

Argue’s team determined, however, that the H. floresiensis individual probably did suffer from a type of microcephaly.

This combination of skull and limb traits raises three possible explanations for the evolution of H. floresiensis, according to Argue’s group. The creature could have originated in Africa as a previously unknown Homo lineage that later migrated to southeastern Asia, or evolved on Flores from an early Homo population that had unusually short limbs, or derived from an ancient African population that was in the process of evolving from Australopithecus to Homo when it departed for Asia.

However, other researchers who have examined Flores fossils (SN: 10/15/05, p. 244: Available to subscribers at Encore for Evolutionary Small-Timers: Tiny human cousins get younger with new finds) and stone tools (SN: 6/3/06, p. 341: Available to subscribers at Stones of Contention: Tiny Homo species tied to ancient tool tradition) regard them as the remains of modern humans with unusual genetic conditions (see “Did small hominids have a genetic defect?” in this week’s issue).

In a joint statement to Science News, Robert B. Eckhardt of Pennsylvania State University in University Park and Maciej Henneberg of the University of Adelaide in Australia call the report from Argue’s team “incomplete and inconclusive.” Eckhardt and Henneberg head a group that has submitted its own analysis of the Flores material and other bones for publication.

Argue’s analysis errs by comparing a mix of pathological and non-pathological traits of the Flores skull and the two microcephalic skulls, Eckhardt and Henneberg contend. It also fails to account for the anatomical effects of a reduced brain size.

“The result is more numerology than objective scientific method,” Eckhardt says.

He suspects that the Stone Age Flores finds came from a population of small-bodied humans that reached the island, with the partial skeleton representing a case of microcephaly.