Neandertals, humans may have grown apart.

A fierce debate revolves around whether Neandertals, who lived in Europe and the Middle East from around 130,000 to 28,000 years ago, belonged to the human species or a separate one.

A new technique for probing fossil anatomy has generated support for the designation of Neandertals as a separate species, according to a report in the Aug. 2 NATURE. Fossil analyses indicate that from infancy to adulthood, the Neandertal skull exhibited a markedly different trajectory of shape changes from that observed in modern humans, say anthropologists Marcia S. Ponce de Leon and Christoph P.E. Zollikofer of the University of Zurich, Switzerland.

"Characteristic differences in cranial and mandibular [jaw] shape between Neandertals and modern humans arose very early during development, possibly prenatally, and were maintained throughout [life]," the researchers conclude.

Other scientists admire the sophisticated computer modeling of cranial growth employed in the new study. However, they disagree about whether this approach establishes that Neandertals developed differently from Homo sapiens.

Ponce de Leon and Zollikofer first took computerized tomography (CT) scans of 16 partial Neandertal skulls, 3 partial H. sapiens skulls dating to about 100,000 years ago, and 22 skulls from still-living human groups.

The Neandertal group included individuals whose age at death ranged from 6 months to several decades. The fossil H. sapiens skulls derived from a child, a teenager, and an adult. The rest of the human skulls came from males and females ranging from infancy to adulthood.

The researchers converted the CT data of each skull into a three-dimensional reconstruction. They then compared shape changes from one age to the next in the computer-rendered skulls for each group.

Neandertals and humans share a generally similar growth pattern for the brain case, face, jaw, and teeth, the investigators note. Still, from the youngest ages to adulthood, Neandertals display substantially faster rates of growth throughout the skull. Cranial features considered typical of Neandertals, such as a long, flat brain case, protruding face, and flat skull floor, appeared within the first few years of life, Ponce de Leon and Zollikofer report.

Other research, led by Daniel E. Lieberman of Harvard University, suggests that early shape changes to the skull floor have far-reaching anatomical effects (SN: 6/2/01, p. 346). Unlike Neandertals, the base of the human skull flexes up near the front during childhood, Lieberman proposes. As this happens, the cranium becomes rounder and the face shortens and retracts.

"Ponce de Leon and Zollikofer are doing terrific work," Lieberman says. "They've shown that Neandertals and humans grow differently from the start."

Jeffrey H. Schwartz of the University of Pittsburgh, another proponent of Neandertals as a separate species, calls the new report "an important advance in analyzing growth patterns in fossils."

However, Milford H. Wolpoff of the University of Michigan in Ann Arbor says that he continues to regard Neandertals as having been part of the human species. Too few juvenile Neandertal fossils exist for a thorough analysis, he notes. Moreover, to confidently show different growth patterns, researchers would need to track the same individuals as they age, an experiment that cannot be done with remains of deceased individuals.

The range of growth patterns in ancient and modern human groups is poorly understood but probably much broader than is often assumed, Wolpoff adds. Even if the new portrayal of Neandertal cranial growth is accurate, it may still fall within the overall scope of human growth patterns, he contends.