Artical on Human Diversity
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Answer:
Explanation: A detailed genetic analysis of more than a thousand human subjects clusters them into five groups corresponding to major geographical regions. This new study shows that self-reported ancestry is a good predictor of one’s genetic make-up.
Since the 18th century, there has been much con-troversy on how one should classify human individuals, and on what basis: physical appearance, skin color or, recently, genetic diversity. The first genetic data on blood group and protein diversity showed that racial categories based on quantitative traits were arbitrary, as the human populations could not be simply divided into a few categories, but rather formed a continuum resulting from the settlement history of our species [1]. More recent molecular studies have allowed us to detail this complex migration and expansion process and put it into a time frame [2., 3., 4.]. Genetic studies have also shown that most of the genetic variability in our species is due to differences between individuals within populations, rather than to differences between populations [5., 6.]. This might be because human populations have not been independently evolving entities, but rather have maintained connections through the exchange of migrants; it also implies that the definition of a human population is somewhat unclear. Despite this ambiguity, most genetic studies have involved the comparison of gene frequencies among different samples assumed to be drawn from different population subdivisions.
The novelty of the recent work of Rosenberg et al.[7] is precisely that they have checked the validity of the population-sampling approach and tried to define the genetic structure of the human population without using a priori information on the geographic origin of the individuals. For that purpose, they used the structure program [8], which attempts to find, for each individual, the proportion of its genome that comes from a given ‘population’, whose unknown genetic constitution is estimated in the same process. This procedure is performed successively with the assumption of an increasing number of ‘populations’ or clusters (K): K = 2, 3, 4 and so on [8].
Rosenberg et al.[7] applied this procedure to 1056 individuals analyzed for 377 autosomal short tandem repeat (STR) loci. This data set is the first outcome of the analysis of a cell-line panel of 52 worldwide populations [9] managed by the French Center for the Study of Human Polymorphism (CEPH) in the framework of the Human Genome Diversity Project initiated by Luca Cavalli-Sforza. This is by far the largest multi-locus data set presently available for humans.
The results obtained by Rosenberg et al.[7] are quite remarkable. For K = 2 case, where it is assumed that there are two clusters, a contrast is found between individuals from sub-Saharan Africa and native Amerindians. Individuals from other regions seem to harbor various proportions of ‘African’ genes, with a tendency to a dilution of these genes with distance from Africa
Answer:
The evolution of modern humans was a complex process, involving major changes in levels of diversity through time. The fossils and stone tools that record the spatial distribution of our species in the past form the backbone of our evolutionary history, and one that allows us to explore the different processes—cultural and biological—that acted to shape the evolution of different populations in the face of major climate change. Those processes created a complex palimpsest of similarities and differences, with outcomes that were at times accelerated by sharp demographic and geographical fluctuations. The result is that the population ancestral to all modern humans did not look or behave like people alive today. This has generated questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of Homo sapiens. The paucity of African fossils remains a serious stumbling block for exploring some of these issues. However, fossil and archaeological discoveries increasingly clarify important aspects of our past, while breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of Late Quaternary Eurasian hominin groups and their interactions, as well as those between foragers and farmers. This paper explores the nature and timing of key moments in the evolution of human diversity, moments in which population collapse followed by differential expansion of groups set the conditions for transitional periods. Five transitions are identified (i) at the origins of the species, 240–200 ka; (ii) at the time of the first major expansions, 130–100 ka; (iii) during a period of dispersals, 70–50 ka; (iv) across a phase of local/regional structuring of diversity, 45–25 ka; and (v) during a phase of significant extinction of hunter–gatherer diversity and expansion of particular groups, such as farmers and later societies (the Holocene Filter), 15–0 ka.
This article is part of the themed issue ‘Major transitions in human evolution