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...attributes are assumed to be more closely related than populations expressing many differences. Consequently, the pattern of evolutionary relationships among populations allows us to infer processes that determine population structure, such as gene flow and genetic drift, as well as genetic changes resulting from nonrecurrent events, such as expansion, contraction, and population replacement, which constitute the population history (Relethford and Lees 1982; Templeton 1998; Templeton et al. 1995). These evolutionary relationship studies deal with populations at different scales of comparison, some of them focusing on the estimation of relationship between the continental groupings (e.g., Cavalli-Sforza et al. 1994; Nei and Roychoudhury 1993; Relethford 1994; Roseman 2004) and others emphasizing temporal or geographic continuity and/or differentiation among local populations (e.g., Goicoechea et al. 2001; Konigsberg and Buikstra 1995; Relethford and Crawford 1995; Tatarek and Sciulli 2000).
Different kinds of biological traits have been used to infer evolutionary relationships among taxa, including morphological, behavioral, physiological, chemical (proteins, blood groups, and nuclear loci), and ecological (Sneath and Sokal 1973) traits. One of the main criteria for selecting such traits is their heritability, which should be as close to 1 as possible (Cavalli-Sforza et al. 1994; Lieberman 1999). Likewise, the traits must be free from the action of natural selection; that is, they should follow a neutral model of evolution (Cavalli-Sforza et al. 1994; Gonzalez-Jose et al. 2005; Relethford 2004; Relethford and Lees 1982). Because of these requirements, since the early 1970s the focus of research has shifted toward the use of multiple proteins or blood groups as well as nuclear and mitochondrial DNA to infer evolutionary relationships (Cann et al. 1987; Cavalli-Sforza et al. 1994; Wainscoat et al. 1986). Recently, the relationships established by mtDNA have been preferred because mtDNA is not only free from natural selection but also maternally inherited; that is, mtDNA does not undergo recombination and is transmitted intact from mother to offspring (Case and Wallace 1981; Giles et al. 1980; Pakendorf and Stoneking 2005). The changes in mtDNA are mainly due to point mutations (Brown et al. 1979), insertions, and deletions, with the last two events being rare (Ballard et al. 2002).
Although several types of data can be used in living populations, the study of evolutionary relationships in prehistoric populations had been limited to morphological (e.g., cranial and dental) data until the recent advances in the ancient DNA field (Paabo 1985, 1986). However, the potential application of human ancient DNA is limited because most archeological remains contain little endogenous DNA and are often contaminated by modern human DNA and because samples of adequate size needed to compare the frequency of haplotypes are generally not available (Hofreiter and Vigilant 2003; Kaestle and Horsburgh 2002; Kolman and Turos 2000; Stone 2000). Consequently, except in unusual circumstances, most fossils remain within the domain of morphological study (Hillis 1987).
Because morphological data offer the only insight into evolutionary processes when genetic information cannot be recovered, it becomes necessary to establish the reliability of relatedness patterns based on such traits. Several investigators have stated that morphological data have little utility for evolutionary relationship reconstruction at the intraspecific level because of phenotypic plasticity (Cavalli-Sforza et al. 1994; Collard and Wood 2000; Lieberman 1999; Lycett and Collard 2005). However, other investigators have suggested that phenotypic morphometric variation among human populations tends to reflect the underlying genetic variation (e.g., Lockwood et al. 2004; Relethford 1994, 2004; Roseman 2004). Most of these researchers focus on global patterns of variation and find that, at this scale, the degree of differentiation is essentially the same in genetic and craniometric traits (Relethford 1994; Relethford and Harpending 1994), suggesting that the action of neutral evolutionary forces can explain both variables. However, few investigators have compared the evolutionary relationships constructed on the basis of molecular and morphological data. Thus the results obtained by Gonzalez-Jose et al. [2004; see also Gonzalez-Jose (2003)] at the global scale show that genetic and morphometric distance matrices are correlated, whereas the relatedness pattern obtained from these matrices is slightly different. Such contrasting results indicate that more exhaustive analyses are required to establish the accuracy of morphometry-based evolutionary relationships between populations at different geographic scales.
Almost all the studies about evolutionary relationships among human populations that use morphometric data are based on craniofacial linear measurements (Howells 1989; Relethford 1994; Relethford and Harpending 1994). However, in recent years other techniques, such as geometric morphometrics (Adams et al. 2004; Rohlf and Marcus 1993), which captures the geometry of morphological structures and preserves this information throughout the analyses (Rohlf 2000b), have been developed. The most widely used geometric morphometric methods are landmark-based approaches that use sets of two- or three-dimensional coordinates of biological landmarks (Bookstein 1996, 1998). Because of the limitation of landmark methods to analyze the shape of some structures with no or few anatomical points, Bookstein (1997) and Green (1996) proposed the sliding semilandmark method to capture and analyze outlines. Such an approach allows analysis of outlines using the techniques developed for landmark-based analysis with the addition of points called semilandmarks. This approach combines the use of landmarks and semilandmarks in the same statistical analysis and is a powerful tool for describing shape variation in biological structures with few or no landmarks (Bookstein 1997).
Taking into account the mentioned issues, we set a primary goal for this study of testing the reliability of relatedness patterns constructed on the basis of craniometric data in the study of modern human populations on a regional scale. If the morphometric data allow us to infer evolutionary relationships among populations in a particular geographic area, then the obtained relatedness pattern will be the same as the one obtained with molecular data. In particular, we analyze samples from populations belonging to the Chaco, Pampa, and Patagonia regions of South America (Figure 1) for which craniometric and molecular data are available. We compare a relatedness pattern built with molecular data and strongly supported by linguistic and ethnohistorical data and geographic distribution (Goicoechea et al. 2001) with a relatedness pattern built on facial morphological data obtained using geometric morphometric techniques.
[FIGURE 1 OMITTED]
Chaco, Pampa, and Patagonia Populations and Their Evolutionary Relationships
The samples analyzed in this work correspond to several recent groups of Argentina distributed over three geographic and ecological regions: Chaco, Pampa, and Patagonia (Figure 1). Such regions were inhabited in historical times by several groups: The Toba, Mataco, and Choroti groups come from Chaco, the Mapuche group comes from Pampa, and finally, the Tehuelche group comes from Patagonia.
Geographically, the Chaco region is a depressed area drained by the Paraguay, Pilcomayo, Bermejo, and Salado rivers (Figure 1). The native inhabitants of the region lived in small groups made up of a few families, and their subsistence was mainly based on hunting, fishing, and gathering with a small incorporation of cultigens. Some of the species commonly hunted and fished were brocket deer (Mazama gouazoupira), nandu (Rhea americana), vizcacha (Lagostomus maximus), and fishes such as sabalo (Prochilodus sp.) and catfish. The main plant species gathered were algarroba (Prosopis alba), chanar (Gourleia decorticants), and cucurbitaceans (Mashnshnek 1974). The species cultivated were maize (Zea mays), squash penka (Cucurbita sp.), and kidney beans (Phaseolus sp.). The original abode of the Toba was the region between the lower Pilcomayo and Bermejo rivers, but until the end of the 19th century some bands roamed south of the Bermejo River as far as the provinces of Santa Fe and Santiago del Estero. The habitat of the Mataco has remained almost...
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