For scientists who study human evolution, fossil remains provide the only direct evidence

of our ancient ancestors. Access to these paleoanthropological Rosetta stones, how- ever, is limited by protective curators who are often reluctant to lend the fragile fossils. And in the case of fossil skulls, nature preserves critical information in the largely in- accessible interior. But help is on the way. At the annual meeting of the American Association of Physical Anthropologists in Salt Lake City this past April, researchers discussed how medical imaging, virtual reality and computer-controlled modelling technologies get around these obstacles noninvasively.

Three-dimensional medical imaging based on computed tomography (CT) scans was developed in the early 1980s. On a computer, surgeons could electronically remove the patient's soft tissue and then explore the virtual skull inside and out before operating. It wasn't long before Glenn Conroy of Washington University and his colleagues demonstrated that these same techniques could also be applied to fossils, in which sediments take the place of soft tissue.

With advances in computer graphics and computational power, paleoanthropologists can now perform. on their computers a wide range of investigations that are impossible to attempt on the original fossil. Missing features on one Side of the skull can be re-created by mirroring the preserved features (postmortem deformations can be similarly rectified) and tiny, hidden structures such as the inner ear can be magnified for closer examination. Moreover, as Christoph P. E. Zollikofer and Marcias Ponce de Leon of the University of Zurich and others have shown, anthropologists can reconstruct fragmented fossils on-screen.

The standard repertoire of measurements can also be made virtually, in most cases with the same degree of accuracy afforded by handheld calipers. And with the creation of a virtual "endocast", brain volume can be determined reliably. In fact, Conroy's recent re- Search has revealed a major discrepancy between the estimated and actual brain volume of an early hominid called Stw 505 (or Mr. Pies). Conroy suspects that the estimated cranial capacity of some other fossils might also be incorrect--a hunch that, if substantiated, could have important implications for our understanding of brain evolution.

The article could be entitled

A．Human Evolution

B．Virtual Fossil Skull

C．Three-dimensional Medical Imaging

D．Virtual Anthropology