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Author Topic: Cranio-metric similarities within and between populations compared with genetic data
Calabooz '
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Been browsing the online Journals, and this caught my eye:

Craniometric Similarities Within and Between Human
Populations in Comparison with Neutral Genetic Data André Strauss and Mark Hubbe (2010)

quote:
Abstract The statement that pairs of individuals from different populations are often more genetically similar than pairs from the same population is a widespread idea inside and outside the scientific community. Witherspoon
et al. [“Genetic similarities within and between human populations,” Genetics 176:351–359 (2007)] proposed an index called the dissimilarity fraction (ω) to access in a quantitative way the validity of this statement for genetic
systems. Witherspoon demonstrated that, as the number of loci increases, ω decreases to a point where, when enough sampling is available, the statement is false. In this study, we applied the dissimilarity fraction to Howells’s craniometric database to establish whether or not similar results are obtained for cranial morphological traits. Although in genetic studies thousands of loci are available, Howells’s database provides no more than 55 metric traits, making the contribution of each variable important. To cope with this limitation, we developed a routine that takes this effect into consideration when calculating ω. Contrary to what was observed for the genetic data, our results show that cranial morphology asymptotically approaches a mean ω of 0.3 and therefore supports the initial statement—that is, that individuals from the same geographic region do not form clear and discrete clusters—further questioning the idea of the existence of discrete biological clusters in the human species. Finally, by assuming that cranial morphology is under an additive polygenetic model, we can say that the population history signal of human craniometric traits presents the same resolution as a neutral genetic system dependent on no more than 20 loci.

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Posts: 1502 | From: Dies Irae | Registered: Oct 2010  |  IP: Logged | Report this post to a Moderator
Calabooz '
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The Linear Measurements of the Neurocranium Are Better Indicators of Population Differences than Those of the Facial Skeleton: A Comparative Study of 1961 Skulls

Gábor Holló et al., (2010)


quote:
Abstract
The aim of the study was to individualize potential differences between two cranial regions in differentiating human populations. The neurocranium and the facial skeleton were compared to each other. Skulls from the Great Hungarian Plain were examined. They are dated back to the 1st – 11th centuries, a long space of time that encompasses seven archaeological periods. We analyzed six neurocranial and seven facial measurements. The reduction of the number of variables was carried out by Principal Components Analysis. Linear mixed-effects models (LMM) were fit to the principal components of each archaeological period, and then the models were compared by multiple pairwise tests. The neurocranium showed significant differences in seven cases between non-subsequent periods, and, in one case, between two subsequent populations. In the case of the facial skeleton, no significant results were found. Our results, which are also compared to previous craniofacial heritability estimates, suggest that the neurocranium is a more conservative region, and population differences can be pointed out better by the neurocranium than by the facial skeleton.

And from the same article, we have:

quote:
Discussion and Conclusions
The results of our analyses suggest that the measurements of the neurocranium
carry relevant information about the differentiation of diverse populations,
whereas the facial skeleton does so to a minor extent.
A possible explanation of this difference between the two regions is that during ontogenesis, the neurocranium attains adult size and shape earlier than the facial skeleton does (Bastir et al. 2006, 2007; Bookstein et al. 2003; Sardi and Ramírez Rozzi 2005; Zollikofer and Ponce de León 2002). Consequently, the facial skeleton is exposed to environmental factors that are different from those acting on the neurocranium during its development, and for a longer time. Accordingly, the development of the face is expected to be more plastic compared to the development of the neurocranium (Bastir and Rosas 2004; Bastir et al. 2006;Kohn 1991; Strand Viðarsdóttir et al. 2002), and thus it can be expected that some genetically based population differences are better revealed by the neurocranium than by the face (Harvati and Weaver 2006).

So, basically it looks like Neurocranium is more likely to stay, homogeneous so to speak, amongst populations developed within the same environment, as environmental factors don't affect Neurocranium as much as it does facial cranium. Does anybody have any info on this in regards to Africa groups?

http://www.sendspace.com/file/og733m

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Posts: 1502 | From: Dies Irae | Registered: Oct 2010  |  IP: Logged | Report this post to a Moderator
   

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