They owe that belief to the work of Franz Boas, the famed anthropologist whose landmark 1912 study showed that skull dimensions were the product of forces such as early childhood nutrition, not racial heritage.
Alas, it seems Boas might have gotten it backwards.
Two American anthropologists have reanalyzed his data, and found the oft-cited scientist overstated the effects of environment and vastly downplayed the importance of genes.
To be sure, Boas may have been handicapped by the lack of computing power to crunch such a large pool of numbers; he collected nearly 13,000 measurements for his project. However, he was a sophisticated statistician who knew what he was doing.
"In the end, he could have ascertained that the ethnic component of variation is large in comparison to the immigration component. But that's not what he was interested in," says Richard Jantz, an anthropologist at the University of Tennessee and a co-author of the latest work. "It does appear that he knew what he wanted to get out of this study, and he was pretty determined to get it."
Jantz and his colleague, Corey Sparks, a doctoral student in anthropology at Penn State University, report their findings this week in the Proceedings of the National Academy of Sciences.
At the end of the 19th century and into the early years of the 20th, racists used the mantle of science to justify their belief that blacks and immigrants were inferior to "true" Americans such as the Anglo-Saxons. One school argued that head shape and size reflected intelligence, aptitude and other traits.
Opponents of this scientific racism were more than cheered by a report from someone of Boas' stature that undercut the movement.
Boas had taken head and face measurements from people belonging to seven European nationalities and ethnic groups: Central Italians and Sicilians, Czechs, Hungarians/Slovakians, Poles, Scots and "Hebrews" from across Eastern Europe.
To assess the impact of environment on head shape -- including skull length and breadth and the breadth of the face -- Boas studied both parents born in the Old World and their American-born children. "The design was wonderful," says Jantz, who along with Sparks analyzed 8,000 of the original subjects.
Boas, Sparks says, found differences between his American-born and European-born subjects of about 2 millimeters to 3 millimeters, on average. "When you're talking about human variation, 2 to 3 millimeters isn't very much. To really support [Boas' argument] you would need to see a fairly dramatic change," he explains.
Ultimately, Jantz contends, about 99 percent of the variation in face and head shape between races that Boas found was inherited; only 1 percent could be attributed to environmental effects such as nutrition.
Jantz says he and Sparks couldn't have done their study had Boas not taken the extraordinary step of publishing his data, giving future scientists the chance to see what he'd done. "The strange thing is it took so long for that to happen," Jantz adds. Boas also measured stature, numbers Sparks is currently reviewing for a follow-up study.
George W. Stocking, Jr., an anthropologist at the University of Chicago and a leading Boas scholar, says he wasn't able to critique Jantz's paper from a technical perspective. However, he says the work is likely to roil modern-day Boasians.
"The last 10 years or so have seen a strong reassertion of biology as a significant factor in human differentiation," says Stocking. "Many anthropologists feel concerned about this, and their tendency is to be very suspicious and very critical of any argument of this sort. It's quite likely there will be a response to this."
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