Multivariate apportionment of global human craniometric diversity

Abstract

Extensive research in human genetics on presumably neutral loci has shown that the overwhelming majority of human diversity is found among individuals within local populations. Previous apportionments of craniometric diversity are similar to these genetic apportionments, implying that interregionally differing selection pressures have played a limited role in producing contemporary human cranial diversity. Here we show that when cranial variation is independently partitioned using principal components analysis of Mosimann shape variables, some estimates of interregional craniometric differentiation are larger than those for most genetic loci. These estimates are similar to estimates for genetic loci where interregionally differing selection pressures are implicated in producing the observed patterns of variation within and among regions. These results suggest that differences among regions in at least some cranial features, particularly in the nasal region, are in part the product of interregionally differing selection pressures. Moreover, these results have implications for assessing the biological affinities of prehistoric samples that are temporally separated from contemporary human reference populations.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

“…Most of the high Fst variables showing a correlation with climate were located on the face, with a few also reflecting neurocranial breadth, again agreeing with previous work (Coon et al, 1950;Carey and Steegmann, 1981;Beals et al, 1983;Franciscus and Long, 1991;Roseman, 2004;Roseman and Weaver, 2004;Harvati and Weaver, 2006a,b). They comprise measurements of facial breadth and height, as well as the nasal dimensions and simotic subtense.…”

“…First, the fact that we chose to consider as significant only those variables with Fst values higher than 0.3 means that our conclusions are centered on diversifying evolutionary forces. As stated by Roseman (2004) and Roseman and Weaver (2004), stabilizing selection could also be affecting general morphological trends in modern humans. Such stabilizing selection would result in a reduction of Fst estimates for those variables or anatomical regions affected.…”

“…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.…”

“…The relevance of cranial morphology to phylogenetic reconstruction has been questioned in the past (see e.g., Collard and Wood, 2000), and convergence, parallelism, reversals, and environmen-tal plasticity are commonly cited as obscuring any phylogenetic signal that it may preserve. The effects of mastication and climatic adaptation on the cranium are thought to be particularly extensive, with some anatomical regions or measurements believed to be affected differentially by these processes (e.g., Hylander, 1977;Carey and Steegmann, 1981;Olson, 1981;Beals et al, 1983;Skelton and McHenry, 1992;Larsen, 1999;Wood and Lieberman, 2001;Lieberman et al, 2004;Roseman, 2004;Roseman and Weaver, 2004;Gonzá lez-José et al, 2005;Harvati and Weaver, 2006a,b;Sardi et al, 2006).…”