A reassessment of human cranial plasticity: Boas revisited

Abstract

In 1912, Franz Boas published a study demonstrating the plastic nature of the human body in response to changes in the environment. The results of this study have been cited for the past 90 years as evidence of cranial plasticity. These findings, however, have never been critiqued thoroughly for their statistical and biological validity. This study presents a reassessment of Boas' data within a modern statistical and quantitative genetic framework. The data used here consist of head and face measurements on over 8,000 individuals of various European ethnic groups. By using pedigree information contained in Boas' data, narrow sense heritabilities are estimated by the method of maximum likelihood. In addition, a series of t tests and regression analyses are performed to determine the statistical validity of Boas' original findings on differentiation between American and European-born children and the prolonged effect of the environment on cranial form. Results indicate the relatively high genetic component of the head and face diameters despite the environmental differences during development. Results point to very small and insignificant differences between European-and American-born offspring, and no effect of exposure to the American environment on the cranial index in children. These results contradict Boas' original findings and demonstrate that they may no longer be used to support arguments of plasticity in cranial morphology.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

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Chinese immigrant population history in North America based on craniometric diversity

“…Various studies have published the heritability estimates of craniometric traits (Sjøvold, 1984;Devor, 1987;Sparks and Jantz, 2002). According to Relethford and Harpending (1994), heritabilities for craniometric traits are fairly stable across populations, and an average estimation of h 2 = 0.55 can be used (Devor, 1987).…”

A bioarchaeological study of mid-Holocene communities in the Eastern Cape, South Africa: the interface between foraging and pastoralism

“…Guglielmino-Matessi et al 1979;Beals et al 1983;Franciscus and Long 1991;Smith et al 2007), similarities in cranial form are generally assumed to reflect common biological affinity (cf. Howells 1995;Lahr 1996;Sparks and Jantz 2002;Relethford 2004;Roseman and Weaver 2004). Cranial and dental remains are not as directly affected by behaviour and activity (as compared to the postcranial skeleton) so they should preserve genetic information more directly.…”

“…However, selecting quantitative traits that are known to be under stronger genetic control, and thus highly heritable, can minimize the environmental influences on the expression of phenotypic traits. Even though cranial and dental quantitative traits are under greater genetic control and are not as plastic as other areas of the skeleton (Sparks and Jantz 2002), cranial and dental traits vary to a certain degree in their heritability. A conservative assumption of the heritability value, like 0.55, is believed to adequately account for this variation (Relethford 1994 heritabilities can also reflect an existing lack of genetic variation in a population resulting from natural selection, inbreeding and genetic drift (Stojanowski and Schillaci 2006: 59).…”