1,721,184 research outputs found
6. Renfrew (C.) et Wagstaff (M.), An Island Polity. The archaeology of exploitation in Melos
No full textVial Claude. 6. Renfrew (C.) et Wagstaff (M.), An Island Polity. The archaeology of exploitation in Melos. In: Revue des Études Grecques, tome 96, fascicule 455-459, Janvier-décembre 1983. pp. 297-298
Genetic variation in North Africa and Eurasia: Neolithic demic diffusion vs. paleolithic colonisation
No full textThe hypothesis that both genetic and linguistic similarities among Eurasian and North African populations are due to demic diffusion of neolithic farmers is tested against a wide database of allele frequencies. Demic diffusion of farming and languages from the Near East should have determined clines in areas defined by linguistic criteria; the alternative hypothesis of cultural transmission does not predict clines. Spatial autocorrelation analysis shows significant gradients in three of the four linguistic families supposedly affected by neolithic demic diffusion; the Afroasiatic family is the exception. Many such gradients are not observed when populations are jointly analyzed, regardless of linguistic classification. This is incompatible with the hypothesis that major cultural transformations in Eurasia (diffusion of related languages and spread of agriculture) took place without major demographic changes. The model of demic diffusion seems therefore to provide a mechanism explaining..
Phylogenetic star contraction applied to Asian and Papuan mtDNA evolution
No full textIn the past decade, mitochondrial DNA (mtDNA) of 826 representative East Asians and Papuans has been typed by high-resolution (14-enzyme) restriction fragment length polymorphism (RFLP) analysis. Compared with mtDNA control region sequencing, RFLP typing of the complete human mitochondrial DNA generally yields a cleaner phylogeny, the nodes of which can be dated assuming a molecular clock. We present here a novel star contraction algorithm which rigorously identifies starlike nodes (clusters) diagnostic of prehistoric demographic expansions. Applied to the Asian and Papuan data, we date the out-of-Africa migration of the ancestral mtDNA types that founded all Eurasian (including Papuan) lineages at 54,000 years. While the proto-Papuan mtDNA continued expanding at this time along a southern route to Papua New Guinea, the proto-Eurasian mtDNA appears to have drifted genetically and does not show any comparable demographic expansion until 30,000 years ago. By this time, the East Asian, Indian, and European mtDNA pools seem to have separated from each other, as postulated by the weak Garden of Eden model. The east Asian expansion entered America about 25,000 years ago, but was then restricted on both sides of the Pacific to more southerly latitudes during the Last Glacial Maximum around 20,000 years ago, coinciding with a chronological gap in our expansion dates. Repopulation of northern Asian latitudes occurred after the Last Glacial Maximum, obscuring the ancestral Asian gene pool of Amerinds
Incorporating environmental heterogeneity in spatially-explicit simulations of human genetic diversity
No full textWe recently developed a simulation framework (SPLATCHE) to model the past demography of human population and the resulting genetic diversity at neutral markers. Additional to range expansions and population subdivisions, we increase here the realism of our simulations by incorporating spatial and temporal heterogeneity of the environment. This heterogeneity can be translated into maps of carrying capacities (maximum density of individuals) and frictions (difficulty of moving) that will in turn influence the size of local populations and the direction and the intensity of migrations. We have considered the influence of several environmental variables: the type of vegetation directly affects the available resource and therefore the carrying capacities; streams and coastlines act as migration corridors with higher carrying capacities than the surrounding environment; a rough topography may also drastically influence migrations. We discuss in this paper each of these environmental variables and how one can estimate carrying capacities and friction values for each of them. We also present an innovative way of considering dynamic changes of vegetation through temporal vegetation heterogeneity. Finally, we examine how environmental heterogeneity might affect genetic differentiation of human populations, and discuss the limitations and perspectives of our approach
Genetic simulations of population interactions during past human expansions in Europe
No full textTwo prehistoric demographic events profoundly affected human species in Europe. The first one is the replacement of Neanderthals by early modern humans from around 45,000 to 30,000 years ago and the second one corresponds to the Neolithic transition around 10,000 years ago. Both events entail to the arrival of new individuals coming from the East and the successive disappearance of pre-existing local people. In both cases the main question is how large was the contribution of pre-existing populations to the genetic pool of contemporary Europeans. In order to answer this question, we developed a new approach allowing the simulation of interactions between two populations (competition, admixture and assimilation) during a colonization phase and the resulting genetic structure of the remaining population. We applied this methodology to both the Neanderthal disappearance and the Neolithic transition by testing many different demographic scenarios. Our results showed that there were probably no genetic exchanges between Neanderthals and modern humans and that they therefore may have constituted two different species. We also showed no genetic evidence for a large replacement of European pre-existing hunter-gatherer populations during the Neolithic transition. Finally we point out the importance of taking in consideration the type of genetic markers used for the analysis as they can reveal very different patterns
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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