"After Boas published his study in 1912, everyone said you cannot use cranial measurements to tell differences in populations," says Corey Sparks, graduate student in anthropology at Penn State. "Uncritical acceptance of his findings has resulted in 90 years of misunderstanding about the magnitude of (cranial) plasticity."
Cranial plasticity is the idea that the dimension of the head, the measurements across the face, the head length and head breadth and the cranial index – a ratio of head length to breadth, change readily with environmental factors.
Sparks, working with Richard Jantz, professor of anthropology, University of Tennessee, looked at the data from Boas' "Report presented to the 61st Congress on Changes in Bodily Form of Descendants of Immigrants," which was published by Columbia University Press in 1928 as "Materials for the Study of Inheritance in Man." The data contain information on head measurements, on approximately 13,000 European-born immigrants and American-born children from the New York City area. The data were divided into seven population groups -- Bohemians, Central Italians, Poles, Hungarians, Scots, Sicilians and a group composed of individuals of Jewish ancestry from Western Russia, Poland, Germany, Austria, Switzerland and Romania. No one had analyzed the data since Boas' days.
Boas claimed in a 1912 American Anthropology article that there were dramatic effects on cranial form depending on the time of exposure to the American environment and that it was not heredity but environment that caused differences.
"Reanalysis of Boas' data not only fails to support his contention that cranial plasticity is a primary source of cranial variation, but rather supports what morphologists and morphometricians have known for a long time, that most of the variation is genetic variation," the researchers report in today's (Oct. 7) issue of Proceedings of the National Academy of Science.
According to the researchers, about ten years before the immigrant study, Boas was one of the most statistically and quantitatively oriented anthropologists, but in the final report presented to congress, Boas's statistical fluency disappeared.
"Boas did some analysis, but he did not do statistical analysis," says Sparks. "While Boas did not have the statistical tools we have today, he did know about standard error, means, averages and variances, but he fails to utilize these properly in his study."
Sparks and Jantz performed standard statistical tests such as univarient t-tests and least square regressions. T-tests that assessed the differentiation among the three cranial measurement and the cranial index of the American-born and European-born children showed that there was only a significant difference in 11 of the 156 tests and these were all in the Jewish population. The regression of the cranial index on age and environment shows only a very small effect of environment.
"The predominant trend in the data suggests a much more significant effect of age on the cranial index rather than of duration of American residence," the researchers say. "This suggests an overall stability of the cranial index in response to changing environment and fails to support the propositions of Boas."
Because of the detail of the data set, the researchers were able to look at hereditability. Data was available on multiple generations of families and so the likelihood that the head length, breadth, and face breadth characteristics were inherited could be tested. While the researchers found a slightly higher environmental component in the facial breadth component, all three measurements showed most of the variation attributable to genetic factors.
"We found that the dominant force for all traits was genetic," says Sparks. "So whereas, based on Boas' report one could not use cranometric measurements to look at populations, our data suggests that one can, which has immediate repercussions for forensic anthropology and such analyses as those of Kennewick Man and other very early human remains. Opponents can no longer cite Boas as an indication that skeletal analysis is unacceptable or inaccurate."
Why was Boas wrong? The researchers suggest that the sheer size of the data set could have been part of the problem. However, they also note that Boas showed "disdain for the often racist ideas in anthropology" at that time and his view that this racist approach should end might have influenced his analysis and presentation. If so, his report, if not putting an end to scientific racism, did serve to make it more difficult to use cranial measurements to further racist ideas.
Sparks and Jantz "make no claim that Boas made deceptive or ill-contrived conclusions" in his report, because they acknowledge that differences between the American and European-born samples exist. They do claim that the data, subjected to modern analysis, do not support Boas' statements about environmental influence on cranial form.
"We performed statistical comparisons that rarely showed any significant difference between the American and European born, but did show some significance to both family and population, indicating a genetic rather than environmental cause."
Journal
Proceedings of the National Academy of Sciences