Craniometric variation among modern human populations

Abstract

Previous studies of genetic markers and mitochondrial DNA have found that the amount of variation among major geographic groupings of Homo sapiens is relatively low, accounting for roughly 10% of total variation. This conclusion has had implications for the study of human variation and consideration of alternative models for the origin of modern humans. By contrast, it has often been assumed that the level of among-group variation for morphological traits is much higher. This study examines the level of among-group variation based on craniometric data from a large sample of modern humans originally collected by W. W. Howells. A multivariate method based on quantitative genetics theory was used to provide an estimate of FST--a measure of among-group variation that can be compared with results from studies of genetic markers. Data for 57 craniometric variables on 1,734 crania were analyzed. These data represent six core areas: Europe, Sub-Saharan Africa, Australasia, Polynesia, the Americas, and the Far East. An additional set of analyses was performed using a three-region subset (Europe, Sub-Saharan Africa, and the Far East) to provide comparability with several genetic studies. The minimum FST (assuming complete heritability) for the three-region analysis is 0.065, and the minimum FST for the six-region analysis is 0.085. Both of these are less than the average FST from genetic studies (average estimates of 0.10-0.11). The smaller value of the minimum FST estimates is expected since it provides an estimate of FST expected under complete heritability. Using an estimate of average craniometric heritability from the literature provides an estimate of FST of 0.112 for the three-region analysis and 0.144 for the six-region analysis. These results show that genetic and craniometric data are in agreement, qualitatively and quantitatively, and that there is limited variation in modern humans among major geographic regions.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

“…Table 4 lists the Fst values calculated for the entire set of craniometric measurements and for each of the variables separately. The value obtained (0.21 for h 2 ¼ 0.55) for all measurements considered together, representing overall cranial morphology, is similar (if a little higher) to Fst values published previously for cranial morphology at a worldwide level (Relethford, 1994(Relethford, , 2002. This result shows that increasing the number of population samples, as well as the total number of specimens considered in the analysis, does not affect the observed pattern of apportionment of craniometric variation.…”

“…For this purpose, we calculated minimum Fst estimates (Relethford and Blangero, 1990;Relethford, 1994) for the whole set of variables and for each variable independently, using the 135 populations as the units of analysis. Fst offers a measure of the amount of variation found between the units of analysis in relation to the total variation of the sample expected under neutral evolution (Relethford, 1994). In other words, Fst gives an estimate of the amount of the variation that is a result of the differences observed between units of analysis (e.g.…”

“…The Fst estimate has been originally devised for genetic data; however, it can also be derived from phenotypic data such as craniometric dimensions (Relethford and Blangero, 1990;Relethford, 1994) when the variance matrix for these data is proportional to the variance matrix of the genetic information underlying the phenotypic trait. As heritability (i.e., proportionality between phenotypic and genetic data) of craniometric measurements is usually relatively high (Devor, 1987;Carson, 2006) Relethford (1994Relethford ( , 2002 and the suggestion of Roseman and Weaver (2004), we accepted an Fst value of 0.3 as the threshold of variability that can be accepted as the product of stochastic microevolutionary processes alone. All Fst estimates considered here were based on an equal heritability value of 0.55, following previous studies (Devor, 1987;Relethford, 1994;Roseman and Weaver, 2004).…”

“…As heritability (i.e., proportionality between phenotypic and genetic data) of craniometric measurements is usually relatively high (Devor, 1987;Carson, 2006) Relethford (1994Relethford ( , 2002 and the suggestion of Roseman and Weaver (2004), we accepted an Fst value of 0.3 as the threshold of variability that can be accepted as the product of stochastic microevolutionary processes alone. All Fst estimates considered here were based on an equal heritability value of 0.55, following previous studies (Devor, 1987;Relethford, 1994;Roseman and Weaver, 2004). Heritability values are used to correct Fst estimates so that it better reflects the proportionality between the phenotypic and the genetic variance matrices, and would present better estimates of Fst for those traits were the true heritability is known.…”

“…Craniometric data have been found to follow a common geographic pattern with genetic markers, including both classical and microsatellite DNA markers (Relethford, 1994(Relethford, , 2004a(Relethford, , 2009Manica et al, 2007;Betti et al, 2009). These findings have been interpreted as resulting from an isolation-by-distance model of evolutionary diversification.…”