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Going Head-to-Head Over Boas's Data

Science  01 Nov 2002:
Vol. 298, Issue 5595, pp. 942b-943b
DOI: 10.1126/science.298.5595.942b

Studying skull dimensions is commonplace in forensics and paleoanthropology. But two new papers offering diametrically opposed analyses of a classic study by Franz Boas suggest that the technique is still controversial for many anthropologists entwined in the ongoing debate over the relation among genes, environment, and race.

Boas, the father of American anthropology, published a study in 1912 challenging the prevailing belief that ironclad genetic rules govern cranial shapes. He took measurements from 13,000 European immigrants and their offspring living in New York comprising seven ethnic groups, the largest being Hebrews (Jews from Eastern Europe), Bohemians, central Italians, and Sicilians. He compared parent-offspring resemblance in immigrants whose children were born in the United States with those whose children were born in Europe to see whether living in the New World had an effect on skull shape (see graphic).

Using the cephalic index—the ratio of head breadth to head length—Boas found what he saw as a small but significant trend: The U.S.-born children in the four largest groups were more different from their parents than were the foreign-born. Jews, who had “very round head[s],” became more “long-headed,” he reported, while long-headed Italians became more short-headed—“so that both approach a uniform type in this country.” The study is often cited as evidence that humans can't be pigeonholed in racial categories because their morphology is too malleable.

Rudimentary as his statistical methods may have been, “in general, we conclude that Boas got it right,” say Clarence C. Gravlee of the University of Michigan, Ann Arbor, and colleagues in a paper posted online (www.aaanet.org/aa/105-1_gravleeetal.htm) months ahead of its publication in the American Anthropologist. The difference in the two groups of offspring, the authors state, is small but “highly significant.”

Taking their measure.

Two teams of researchers have reanalyzed data (top) from a classic study by Franz Boas of European immigrants in America—and come to contrasting conclusions.

CREDIT: (BOTTOM) BETTMANN/CORBIS

Wrong, say Corey Sparks of Pennsylvania State University, University Park, and his adviser, Richard Jantz of the University of Tennessee, Knoxville. The divergence in the U.S.-born offspring is “negligible” and the influence of the environment “insignificant,” they say in the 7 October Proceedings of the National Academy of Sciences. “Uncritical acceptance of [Boas's] findings has resulted in 90 years of misunderstanding about the magnitude of [cranial] plasticity.”

Sparks doesn't disagree that Boas found a difference in cranial shape between foreign and domestic-born children. And Gravlee does not quibble with Sparks about the high heritability—and, hence, stability—of the trait. But the two sides disagree on whether the differences, although statistically significant, are also scientifically meaningful.

Sparks says that the differences pale when compared with the much greater variation seen among ethnic groups. “About 99% of the variation [among all the groups studied] is due to ethnic variation and 1% to immigration,” Jantz explains. “Boas was right in identifying a small immigration effect,” but that has been confirmed in many subsequent studies, he says. “The real value of Boas's work, as reinterpreted by us, is how small that environmental response is.” Henry Harpending of the University of Utah, Salt Lake City, supports Sparks's analysis, arguing that “with samples this large, almost anything can become statistically significant even if it is not worth any attention.”

Gravlee, however, insists that the numbers confirm Boas's “overarching conclusion,” namely, that “the cephalic index is sensitive to environmental influences and therefore does not serve as a valid marker of racial phylogeny.”

The practical impact of the two papers is not clear. Sparks thinks that his analysis will help those who want to use cranial data to study population history, because the Boas study “has been a burr in our bed for 90 years.” Indeed, Jantz was a plaintiff in the long-running suit by scientists seeking permission to study Kennewick Man, a 9000-year-old skeleton found in 1996 in Washington state.

Anthropologist Alan Goodman of Hampshire College in Amherst, Massachusetts, agrees with Gravlee that it's risky to rely on cranial data to identify the origins of long-gone populations. “The evidence does suggest that crania do change,” he says. “If you want to apply [craniometrics] to Kennewick Man and you know there's instability over a 10-year period, what can you expect over a 9000-year period?” Sparks responds that the instability is largely owing to genetic changes, not plasticity, and that a common ancestor can still be inferred by comparing an ancient skull with a modern one that resembles it.

Heavy media coverage of the Sparks paper prompted the American Anthropological Association to post the Gravlee paper, scheduled for March 2003, on its Web site. The two authors will go head-to-head again in June when the American Anthropologist revisits the issue.

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