Heritability of human cranial dimensions: comparing the evolvability of different cranial regions

Abstract

Quantitative craniometrical traits have been successfully incorporated into population genetic methods to provide insight into human population structure. However, little is known about the degree of genetic and non-genetic influences on the phenotypic expression of functionally based traits. Many studies have assessed the heritability of craniofacial traits, but complex patterns of correlation among traits have been disregarded. This is a pitfall as the human skull is strongly integrated. Here we reconsider the evolutionary potential of craniometric traits by assessing their heritability values as well as their patterns of genetic and phenotypic correlation using a large pedigree-structured skull series from Hallstatt (Austria). The sample includes 355 complete adult skulls that have been analysed using 3D geometric morphometric techniques. Heritability estimates for 58 cranial linear distances were computed using maximum likelihood methods. These distances were assigned to the main functional and developmental regions of the skull. Results showed that the human skull has substantial amounts of genetic variation, and a t -test showed that there are no statistically significant differences among the heritabilities of facial, neurocranial and basal dimensions. However, skull evolvability is limited by complex patterns of genetic correlation. Phenotypic and genetic patterns of correlation are consistent but do not support traditional hypotheses of integration of the human shape, showing that the classification between brachy-and dolicephalic skulls is not grounded on the genetic level. Here we support previous findings in the mouse cranium and provide empirical evidence that covariation between the maximum widths of the main developmental regions of the skull is the dominant factor of integration in the human skull.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

“…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. Although Carson (2006) and Martínez-Abadías et al (2009) published individual heritability estimates (h 2 ) for some of the variables used here, the use of Carson's results for those variables found to have high Fst values with h 2 ¼ 0.55 did not change significantly the results (data not shown). Since both these studies found most h 2 values to be smaller than the one considered here (0.55), Fst estimates using their values would be much higher than the ones presented here.…”

“…Carson (2006) and Martínez-Abadías et al (2009) presented estimates for heritability of craniometric measurements that are in most cases smaller than the usually accepted heritability values of 0.55 (Devor, 1987;Sparks and Jantz, 2002). The consequence of assuming a moderately high and uniform heritability means that we are probably underestimating the number of variables that have real Fst values above the threshold of 0.3.…”

Relaxed genetic control of cortical organization in human brains compared with chimpanzees

“…Narrow-sense heritabilities were estimated, and their significance was tested using likelihood ratio tests. Following other quantitative genetic studies of brain, endocranial, and cranial anatomy in humans and nonhuman primates, age, sex, and the interaction between age and sex were used as covariates (54)(55)(56). Overall brain size also was tested as a covariate in analyses of linear distances and PCs of shape.…”

“…When covariates were significant at the P < 0.10 level, they were retained in final models to calculate heritabilities; they were excluded when not significant. Variables were inverse-normalized before analyses to force normality and to avoid high residual kurtosis (56).…”

Cultural diversification promotes rapid phenotypic evolution in Xavánte Indians

“…The matrices of sex-standardized form, and sex-standardized size-corrected shape distances were labeled PHEN and PHENstd, respectively. Phenotypic Mahalanobis distances were obtained using an average heritability value (h 2 = 0.37) for the eight traits, derived from Martínez-Abadías et al (18). Therefore, these distances can be considered as a proxy to genetic distances (24).…”