Associations Between the Neurocranium and the Foot Bones
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Paper 1 Personally Published on Line by MZGCH, pp. 1-54, September 15, 2018 Limits and Regularity of Morphological Variations in Our Species: Ecological Correlations between Craniofacial Measurements and Environmental Variables Yuji Mizoguchi Physical Anthropologist E-mail: [email protected] Abstract The main purposes are to confirm the limits and regularity of among-group variations in the craniofacial morphology of Homo sapiens sapiens, and, if possible, to determine some of the causes for the regularity. As regards the among-group variation limits, it was found that the principal component (PC) scores for the mean vectors of craniofacial measurements in almost all the samples were located within the ±2 standard deviation ranges of the within-group PC scores based on a single sample. This finding suggests some complicated system or factors controlling the coordination between substructures of the skull (or the body). The principal component analyses (PCAs) of among-group correlations between craniofacial measurements clearly indicate the existence of significant common factors, namely, the robust evidence for regularity in the inter-population variations of craniofacial morphology. In the PCAs of among-group correlations between craniofacial measurements and environmental variables, it was found that cranial breadth, upper facial height, bizygomatic breadth, and nasal height tended to be larger in colder regions of higher latitudes; that basi-bregmatic height and nasal breadth tended to be larger and, inversely, minimum frontal breadth tended to be smaller in the regions more distant from Ethiopia and of lower latitudes where average precipitation was higher and average temperature was also relatively high; and that cranial length and cranial base length tended to be larger in ancient times (for the past 7,000 years). These findings, especially on temperature, precipitation and humidity, were interpreted as the results of our evolutionary adaptation to environments. Path analyses, together with PCAs, suggest the existence of unknown factors for every craniofacial measurement dealt with here. In conclusion, the purposes of the present study were partly achieved. But we must still collect more data of various environmental factors, natural and artificial (cultural, social, etc.) and ancient and modern, to clarify the causality for the formation process of our morphology. Key words: Homo sapiens, Skull, Adaptation, Genetic drift, Limb bones, Temperature, Precipitation, Humidity, Chronological age, Latitude, Great circle distance, Principal component analysis, Bootstrap method, Rank correlation, Path analysis Contents Introduction .................................................................................................................................................. 2 Materials .................................................................................................................. ..................................... 3 Methods .................................................................................................................... .................................... 4 Preparation of craniofacial and limb bone data ........................ ................................................................ 4 Preparation of environmental data ............................................................... ............................................ 5 Multivariate Statistical analysis ......................................... ...................................................................... 6 Methods of calculation ............................................................................ ................................................ 8 Results .............................................................................................................. ............................................ 8 Limits of among-group variation in each measurement .......................................................................... 8 Positions of sample means in within-group multivariate distributions ................................................... 8 Selection of samples for among-group multivariate analyses ................................................................. 10 Among-group covariations of craniofacial, limb bone, and environmental variables ............................ 11 Among-group covariations of craniofacial and environmental variables ……………........................... 11 Path analysis of craniofacial measurements and environmental variables .............................................. 15 ____________________________ © 2018 Yuji Mizoguchi Discussion .................................................................................................................................................... 15 Unimodal distribution of sample means and the limits of among-group variation ................................. 20 Comparison to within-group multivariate distributions ........................................................................... 20 General size factor and regularity in among-group variations …….....…..………..........................….... 21 Deviated distributions of environmental variables ……………………….…..................................….... 21 Environmental influence on the craniofacial morphology …………….....................................…..….... 21 Causes of brachycephalization …………….…................................................................................….... 31 Unknown factors influencing the craniofacial morphology …………….........................................….... 32 Summary and Conclusions ........................................................................................................................... 33 Acknowledgments ........................................................................................................................................ 33 Literature Cited ............................................................................................................................................. 34 Appendices .................................................................................................................................................... 49 Introduction according to the properties of the original variables which are strongly correlated with the common factors in We can judge whether it is human or not by question. Such analyses do not inform us whether the glancing at its morphology. This is probably because common factors extracted are pleiotropic genes, common there are limits and some regularity in the morphological environmental factors, or a composite of them unless any variations of the animal called human being. The candidates of causes for the variations of biological ultimate aim of the present author is to understand the characters under consideration are included in the data mechanism of evolutionary formation of our body sets to be analyzed. structure. As a step to achieve the ultimate aim, it is Recently, however, from another angle, molecular attempted in the present study to confirm the limits and biology made it possible for us to know the regularity of among-group variations in the craniofacial correspondence of some morphological characters with morphology of Homo sapiens sapiens, and, if possible, to gene loci on chromosomes. Dorus et al. (2004) determine some of the causes for the regularity of compiled a list of 27 genes demonstrated to play among-group variations, i.e., for the among-group important roles in the nervous system including the brain, covariations between craniofacial measurements. and discussed the evolution of the human brain. As regards the within-group covariations of Coussens and van Daal (2005) found that a morphological traits, a lot of studies have been carried single-nucleotide polymorphism (htSNP out. For example, Howells (1957, 1972, 1973), Kanda g.8592931G->C) in the gene FGFR1 (fibroblast growth and Kurisu (1967, 1968), Kanda (1968), and Brown factor receptor 1) had a significant negative correlation (1973), using multivariate statistical methods, found that with the cephalic index for all of four populations, i.e., there are some common factors controlling the so-called Caucasian, Asian, Australian Aboriginal, and craniofacial morphology. Furthermore, Mizoguchi African American populations. Evans et al. (2005) (1992, 1994, 1995b, 1996, 1997, 1998a, d, 1999, 2000a, maintain that the gene Microcephalin (MCPH1) regulates 2001, 2002, 2003a, b, 2004a, b, 2005, 2007a, b, 2008, brain size and has evolved under strong positive selection 2009, 2013a) carried out a series of principal component in the human evolutionary lineage. Mekel-Bobrov et al. analyses (PCAs) of within-group correlations between (2005) state that the gene ASPM (abnormal spindle-like cranial and postcranial measurements mainly to elucidate microcephaly associated) is a specific regulator of brain the causes of brachycephalization on the premise that size, and that its evolution was also driven by strong population differences are extensions of individual positive selection in the lineage leading to Homo sapiens. differences, as stated by Howells (1973). As a result, he Liu et al. (2012), using almost ten thousand individuals found several common factors suggesting that, while of European descent, identified five independent genetic cranial breadth has no consistent associations with any loci (at 1p36.23-p33, 2q35, 3q28, 5q35.1, and 10q24.3) postcranial measurements, cranial length is