Evolutionary Shrinkage: Stone Age Homo find offers small surprise

October 27, 2004 at 1:31 pm

Big evolutionary insights sometimes come in little packages. Witness the startling discovery, in a cave on the eastern Indonesian island of Flores, of the partial skeleton of a half-size Homo species that lived there at the same time that ancient Homo sapiens inhabited nearby regions.

LITTLE BIG FIND. The newly discovered Homo floresiensis skull (left) comes up short next to a Homo sapiens skull (right). Brown

The new species, dubbed Homo floresiensis, reached the island at least 38,000 years ago and lived there until it died out near the end of the Stone Age, roughly 20,000 years later, conclude the authors of two papers in the Oct. 28 Nature. The researchers say that the Flores find represents an adult, probably a female, who stood about 3 feet, 3 inches tall (1 meter) and weighed approximately 35 pounds (16 kilograms).

This individual’s brain was only about as large as those of australopithecines, which were apelike members of the human evolutionary family that preceded Homo.

One team, led by Peter Brown of the University of New England in Armidale, Australia, excavated and analyzed the new remains, which include a nearly complete skull, a partial pelvis, and two leg bones. Aside from its small stature and brain, the specimen closely resembles Homo erectus fossils, Brown’s group concludes.

A second team, directed by the University of New England’s Michael J. Morwood, evaluated thousands of stone tools and animal bones dug from the same cave. This team used radiocarbon measurements and three other methods to estimate the discoveries’ age.

Brown’s team proposes that H. erectus reached Flores by 800,000 years ago (SN: 3/14/98, p. 164) and evolved into the smaller species as a result of living on an island with limited food sources. “Future research on Flores will try to find the suspected large-bodied ancestor [of H. floresiensis],” Brown says.

The evolution of smaller creatures from larger ones, referred to as dwarfing, has been documented for nonhuman animals on several islands. For instance, the remains of dwarf elephants and small Komodo dragons have been unearthed on Flores.

It’s unlikely that small individuals on Flores evolved as pygmy versions of H. sapiens, Brown contends. African pygmies stop growing as adolescents, after the bulk of brain growth has occurred, so they possess brains nearly as large as other persons’.

H. sapiens arrived in Australia and nearby islands by at least 55,000 years ago, the scientists add, but it’s not known whether or how these people interacted with their diminutive counterparts.

Anthropologists familiar with the Flores specimen accept it as a new Homo species. “It’s amazingly tiny,” remarks Daniel E. Lieberman of Harvard University. Further research needs to confirm that H. floresiensis‘ small size evolved gradually on the island, he says.

Instead, dwarfing might have occurred rapidly in a Homo species that reached Flores late in the Stone Age, notes Tim White of the University of California, Berkeley.

In a comment published with the new reports, Marta M. Lahr and Robert Foley, both of the University of Cambridge in England, say that the new find strengthens the view that many ancient Homo species evolved throughout the world.

White disagrees with that view (SN: 5/3/03, p. 275: Available to subscribers at Ancestral Bushwhack: Hominid tree gets trimmed twice). Isolation of groups on islands greatly increased anatomical diversity in Homo, but that process didn’t necessarily occur on the mainland, he argues.