النوبة والنوبا

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Abdalla Teia
<aAbdalla Teia
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20 عاما من العطاء و الصمود
مكتبة سودانيزاونلاين
Re: النوبة والنوبا (Re: خالد حاكم)

    هذة دراسة قامت بها جامعة مريلاند الامريكية بالتعاون مع معهد الامراض المتواطنة وقد شاركت انا واستاذى بروفيسور منتصر الطيب ابراهيم وسف فى هذة الدراسة. وتجد اسم واستاذى يحملان الرقم 9


    The Genetic Structure and History of
    Africans and African Americans
    Sarah A. Tishkoff,1,2* Floyd A. Reed,1†‡ Françoise R. Friedlaender,3‡ Christopher Ehret,4
    Alessia Ranciaro,1,2,5§ Alain Froment,6§ Jibril B. Hirbo,1,2 Agnes A. Awomoyi,1and#8741;
    Jean-Marie Bodo,7 Ogobara Doumbo,8 Muntaser Ibrahim,9 Abdalla T. Juma,9 Maritha J. Kotze,10
    Godfrey Lema,11 Jason H. Moore,12 Holly Mortensen,1¶ Thomas B. Nyambo,11 Sabah A. Omar,13
    Kweli Powell,1# Gideon S. Pretorius,14 Michael W. Smith,15 Mahamadou A. Thera,8
    Charles Wambebe,16 James L. Weber,17 Scott M. Williams18
    Africa is the source of all modern humans, but characterization of genetic variation and of
    relationships among populations across the continent has been enigmatic. We studied 121 African
    populations, four African American populations, and 60 non-African populations for patterns of
    variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral
    population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or
    linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting
    historical migration events across the continent. Our data also provide evidence for shared ancestry
    among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The
    ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European
    (~13%), and other African (~8%) populations, although admixture levels varied considerably
    among individuals. This study helps tease apart the complex evolutionary history of Africans and
    African Americans, aiding both anthropological and genetic epidemiologic studies.
    Modern humans originated in Africa
    ~200,000 years ago and then spread
    across the rest of the globe within the
    past ~100,000 years (1). Thus, modern humans
    have existed continuously in Africa longer than
    in any other geographic region and have maintained
    relatively large effective population sizes,
    resulting in high levels of within-population genetic
    diversity (1, 2). Africa contains more than
    2000 distinct ethnolinguistic groups representing
    nearly one-third of the world’s languages (3).
    Except for a few isolates that show no clear relationship
    with other languages, these languages
    have been classified into four major macrofamilies:
    Niger-Kordofanian (spoken across a
    broad region of Africa), Afroasiatic (spoken predominantly
    in Saharan, northeastern, and eastern
    Africa), Nilo-Saharan (spoken predominantly in
    Sudanic, Saharan, and eastern Africa), and
    Khoesan (languages containing click-consonants,
    spoken by San in southern Africa and by Hadza
    and Sandawe in eastern Africa) (fig. S1) (4).
    Despite the importance of African population
    genetics, the pattern of genome-wide nuclear genetic
    diversity across geographically and ethnically
    diverse African populations is largely
    uncharacterized (1, 2, 5). Because of considerable
    environmental diversity, African populations
    show a range of linguistic, cultural, and phenotypic
    variation (1, 2, 4). Characterizing the pattern
    of genetic variation among ethnically diverse
    African populations is critical for reconstructing
    human evolutionary history, clarifying the population
    history of Africans and African Americans,
    and determining the proper design and interpretation
    of genetic disease association studies (1, 6),
    because substructure can cause spurious results
    (7). Furthermore, variants associated with disease
    could be geographically restricted as a result of
    new mutations, genetic drift, or region-specific
    selection pressures (1). Thus, our in-depth characterization
    of genetic structure in Africa benefits
    research of biomedical relevance in both African
    and African-diaspora populations.
    We genotyped a panel of 1327 polymorphic
    markers, consisting of 848 microsatellites, 476
    indels (insertions/deletions), and three SNPs
    (single-nucleotide polymorphisms), in 2432
    Africans from 113 geographically diverse populations
    (fig. S1), 98 African Americans, and 21
    Yemenites (table S1). To incorporate preexisting
    African data and to place African genetic variability
    into a worldwide context, we integrated
    these data with data from the panel of markers
    genotyped in 952 worldwide individuals from the
    CEPH-HGDP (Centre d’and#201;tude du Polymorphisme
    Humain–Human Genome Diversity Panel)
    (8–10) in 432 individuals of Indian descent (11)
    and in 10 Native Australians (tables S1 and S2).
    African variation in a worldwide context.
    African and African American populations, with
    the exception of the Dogon of Mali, show the
    highest levels of within-population genetic diversity
    (q = 4Nem, where q is the level of genetic diversity
    based on variance of microsatellite allele length, Ne
    is the effective population size, and m is the
    microsatellite mutation rate) (figs. S2 and S3). In
    addition, genetic diversity declines with distance
    from Africa (fig. S2, A to C), consistent with
    proposed serial founder effects resulting from the
    migration of modern humans out of Africa and
    across the globe (9, 11–13).Within Africa, genetic
    diversity estimated from expected heterozygosity
    significantly correlates with estimates from microsatellite
    variance (fig. S4) (4) and varies by linguistic,
    geographic, and subsistence classifications
    (fig. S5). Three hunter-gatherer populations (Baka
    Pygmies, Bakola Pygmies, and San) were among
    the five populations with the highest levels of
    genetic diversity based on variance estimates (fig.
    S2A) (4). In addition, more private alleles exist in
    Africa than in other regions (fig. S6A). Consistent
    with bidirectional gene flow (14), African and
    Middle Eastern populations shared the greatest
    number of alleles absent from all other populations
    (fig. S6B). Within Africa, the most private alleles
    were in southern Africa, reflecting those in southern
    African Khoesan (SAK) San and !Xun/Khwe
    populations (fig. S6C) (12). Eastern and Saharan
    Africans shared the most alleles absent from other
    African populations examined (fig. S6D).
    The proportion of genetic variation among all
    studied African populations was 1.71%(table S3). In
    comparison, Native American and Oceanic populations
    showed the greatest proportion of genetic
    variation among populations (8.36% and 4.59%, respectively),
    most likely due to genetic drift (9, 15, 16).
    Distinct patterns of the distribution of variation
    amongAfrican populations classified by geography,
    language, and subsistence were also observed (4).
    RESEARCHARTICLE
    1Department of Biology, University of Maryland, College Park,
    MD 20742, USA. 2Departments of Genetics and Biology,
    University of Pennsylvania, Philadelphia, PA 19104, USA.
    3Independent researcher, Sharon, CT 06069, USA. 4Department
    of History, University of California, Los Angeles, CA 90095, USA.
    5Dipartimento di Biologia ed Evoluzione, Università di Ferrara,
    44100 Ferrara, Italy. 6UMR 208, IRD-MNHN, Musée de
    l’Homme, 75116 Paris, France. 7Ministère de la Recherche
    Scientifique et de l’Innovation, BP 1457, Yaoundé, Cameroon.
    8Malaria Research and Training Center, University of Bamako,
    Bamako, Mali. 9Department of Molecular Biology, Institute of
    Endemic Diseases, University of Khartoum, 15-13 Khartoum,
    Sudan. 10Department of Pathology, Faculty of Health Sciences,
    University of Stellenbosch, Tygerberg 7505, South Africa.
    11Department of Biochemistry, Muhimbili University of Health
    and Allied Sciences, Dar es Salaam, Tanzania. 12Departments of
    Genetics and Community and Family Medicine, Dartmouth
    Medical School, Lebanon, NH 03756, USA. 13Kenya Medical
    Research Institute, Center for Biotechnology Research and
    Development, 54840-00200 Nairobi, Kenya. 14Division of Human
    Genetics, Faculty of Health Sciences, University of
    Stellenbosch, Tygerberg 7505, South Africa. 15Laboratory of
    Genomic Diversity, National Cancer Institute, Frederick, MD
    21702, USA. 16International Biomedical Research in Africa,
    Abuja, Nigeria. 17Marshfield Clinic Research Foundation,
    Marshfield, WI 54449, USA. 18Department of Molecular Physiology
    and Biophysics, Center for Human Genetics Research,
    Vanderbilt University, Nashville, TN 37232, USA.
    *To whom correspondence should be addressed. E-mail:
    [email protected]
    †Present address: Department of Evolutionary Genetics,
    Max Planck Institute for Evolutionary Biology, 24306 Pland#246;n,
    Germany.
    ‡These authors contributed equally to this work.
    §These authors contributed equally to this work.
    ||Present address: Department of Internal Medicine, Ohio
    State University, Columbus, OH 43210, USA.
    ¶Present address: Office of Research and Development,
    National Center for Computational Toxicology, U.S. Environmental
    Protection Agency, Research Triangle Park, NC 27711,
    USA.
    #Present address: College of Education, University of
    Maryland, College Park, MD 20742, USA.
    www.sciencemag.org SCIENCE VOL 324 22 MAY 2009 1035
    Fig. 1. Neighbor-joining tree from pairwise D2
    genetic distances between populations (65). African
    population branches are color-coded according to
    language family classification. Population clusters
    by major geographic region are noted; bootstrap
    values above 700 out of 1000 are indicated by
    thicker lines and bootstrap number.
    1036 22 MAY 2009 VOL 324 SCIENCE www.sciencemag.org
    RESEARCH ARTICLE
    Phylogenetic trees constructed from genetic
    distances between populations generally showed
    clustering by major geographic region, both on a
    global scale and within Africa (Fig. 1 and figs.
    S7 and S8). Within Africa, the two SAK
    populations cluster together and are the most
    distant from other populations, consistent with
    mitochondrial DNA (mtDNA), Y chromosome,
    and autosomal chromosome diversity studies, indicating
    that SAK populations have the most
    diverged genetic lineages (12, 17–21). The Pygmy
    populations cluster near the SAK populations in
    the tree constructed fromD2 genetic distances (Fig.
    1), whereas the Hadza and Sandawe cluster near
    the SAK populations in the tree constructed from
    RST genetic distances (fig. S8) (4). Note that population
    clustering in the tree may reflect common
    ancestry and/or admixture. African populations
    with high levels of non-African admixture [e.g., the
    Cape Mixed Ancestry (CMA) population, commonly
    referred to as “Cape Coloured” in South
    Africa] cluster in positions that are intermediate
    between Africans and non-Africans, whereas the
    AfricanAmerican populations, which are relatively
    less admixed with non-Africans, cluster more
    closely with West Africans. Additionally, populations
    with high levels of genetic drift (i.e., the
    Americas, Oceania, and Pygmy, Hadza, and SAK
    hunter-gatherers) have longer branch lengths.
    Geographic distances (great circle routes)
    and genetic distances (dm)2 between population
    pairs were significantly correlated, consistent
    with an isolation-by-distance model (figs. S9 to
    S11 and table S4) (13). A heterogeneous pattern
    of correlations across global regions was observed,
    consistent with a previous study (16);
    the strongest correlations were in Europe and
    the Middle East (Spearman’s r = 0.88 and 0.83,
    respectively; P and#8804; 0.0001 for both), followed by
    Africa (Spearman’s r = 0.40; P < 0.0001).
    Correlations were not significant for central Asia
    or India.Within Africa, the strongest correlations
    between genetic and geographic distances were
    in Saharan Africa and central Africa (Spearman’s
    r = 0.76 and 0.55, respectively; P < 0.0001 for
    both) (fig. S11 and table S4). The smallest correlation
    was observed in eastern Africa (r = 0.19;
    P < 0.0001).
    Genetic structure on a global level. Global
    patterns of genetic structure and individual ancestry
    were inferred by principal components analysis
    (PCA) (22) (Fig. 2A) and a Bayesian modelbased
    clustering approach with STRUCTURE
    (23) (Figs. 3 and 4 and figs. S12 to S14).
    Worldwide, 72 significant principal components
    (PCs) were identified by PCA (P < 0.05) (22).
    PC1 (accounting for 19.5% of the extracted variation)
    distinguishes Africans from non-Africans.
    The CMA and African American individuals
    cluster between Africans and non-Africans,
    reflecting both African and non-African ancestry.
    PC2 (5.01%) distinguishes Oceanians, East
    Asians, and Native Americans from others. PC3
    (3.5%) distinguishes the Hadza hunter-gatherers
    from others. The remaining PCs each extract less
    than 3% of the variation, and the 22nd to 72nd
    PCs extract less than 1% combined, with some
    minor PCs corresponding to regional and/or
    ethnically defined populations, consistent with
    STRUCTURE results below.
    STRUCTURE analysis revealed 14 ancestral
    population clusters (K = 14) on a global level
    (Figs. 3 and 4) (4). Middle Eastern and Oceanic
    populations exhibit low levels of East African
    ancestry up to K = 8, consistent with possible
    gene flow into these regions and with studies
    suggesting early migration of modern humans
    into southern Asia and Oceania (16, 24). The
    Hadza, and to a lesser extent the Pygmy, SAK,
    and Sandawe hunter-gatherers, are distinguished
    at K = 5. The 11th cluster (K = 11) distinguishes
    Mbuti Pygmy and SAK individuals, indicating
    common ancestry of these geographically distant
    hunter-gatherers.A number of Africans (predominantly
    CMA, Fulani, and eastern Afroasiatic
    speakers) exhibit low to moderate levels of
    European–Middle Eastern ancestry, consistent with
    possible gene flow from those regions. We found
    more African substructure on a global level (nine
    clusters) than previously observed (9–12, 20). A
    phylogenetic tree of genetic distances from inferred
    ancestral clusters (fig. S14) indicates that within
    Africa, the Pygmy and SAK associated ancestral
    clusters (AACs) form a clade, as do the Hadza and
    Sandawe AACs and the Nilo-Saharan and Chadic
    AACs, reflecting their ancient common ancestries.
    Genetic structure within Africa. PCA of
    genetic variation within Africa indicated the
    presence of 43 significant PCs (P < 0.05 with a
    Tracy-Widom distribution). PC1 (10.8% of the
    extracted variation) distinguishes eastern and
    Saharan Africa from western, central, and southern
    Africa (Fig. 2B). The second PC (6.1%)
    distinguishes the Hadza; the third PC (4.9%)
    distinguishes Pygmy and SAK individuals from
    other Africans. The fourth PC (3.7%) is associated
    with the Mozabites, some Dogon, and the
    CMA individuals, who show ancestry from the
    European–Middle Eastern cluster. The fifth PC
    (3.1%) is associated with SAK speakers. The
    10th PC was of particular interest (2.2%) because
    it associates with the SAK, Sandawe, and
    some Dogon individuals, suggesting shared
    ancestry.
    We incorporated geographic data into a Bayesian
    clustering analysis, assuming no admixture
    (TESS software) (25) and distinguished six clusters
    within continental Africa (Fig. 5A). The most
    geographically widespread cluster (orange)
    extends from far Western Africa (the Mandinka)
    through central Africa to the Bantu speakers of
    South Africa (the Venda and Xhosa) and corresponds
    to the distribution of the Niger-Kordofanian
    language family, possibly reflecting the spread of
    Bantu-speaking populations from near the Nigerian/
    Cameroon highlands across eastern and southern
    Africa within the past 5000 to 3000 years (26, 27).
    Another inferred cluster includes the Pygmy and
    SAK populations (green), with a noncontiguous
    geographic distribution in central and southeastern
    Africa, consistent with the STRUCTURE (Fig. 3)
    and phylogenetic analyses (Fig. 1). Another geographically
    contiguous cluster extends across northern
    Africa (blue) into Mali (the Dogon), Ethiopia,
    and northern Kenya. With the exception of the
    Fig. 2. Principal components
    analysis (22)
    created on the basis of
    individual genotypes.
    (A) Global data set and
    (B) African data set.
    www.sciencemag.org SCIENCE VOL 324 22 MAY 2009 1037
    RESEARCH ARTICLE
    Dogon, these populations speak an Afroasiatic
    language. Chadic-speaking and Nilo-Saharan–
    speaking populations from Nigeria, Cameroon,
    and central Chad, as well as several Nilo-
    Saharan–speaking populations from southern Sudan,
    constitute another cluster (red). Nilo-Saharan
    and Cu####ic speakers from the Sudan, Kenya, and
    Tanzania, as well as some of the Bantu speakers
    from Kenya, Tanzania, and Rwanda (Hutu/Tutsi),
    Fig. 3. STRUCTURE analysis of the global data set with 1327 markers
    genotyped in 3945 individuals. Each vertical line represents an individual.
    Individuals were grouped by self-identified ethnic group (at bottom)
    and ethnic groups are clustered by major geographic region (at
    top). Colors represent the inferred ancestry from K ancestral populations.
    STRUCTURE results for K = 2 to 14 (left) are shown with the number of
    similar runs (F) for the primary mode of 25 STRUCTURE runs at each K
    value (right).
    1038 22 MAY 2009 VOL 324 SCIENCE www.sciencemag.org
    RESEARCH ARTICLE
    constitute another cluster (purple), reflecting linguistic
    evidence for gene flow among these
    populations over the past ~5000 years (28, 29).
    Finally, the Hadza are the sole constituents of a
    sixth cluster (yellow), consistent with their distinctive
    genetic structure identified by PCA and
    STRUCTURE.
    STRUCTURE analysis of the Africa data set
    indicated 14 ancestral clusters (Fig. 5, B and C,
    and figs. S15 to S18). Analyses of subregions
    within Africa indicated additional substructure
    (figs. S19 to S29). At low K values, the Africawide
    STRUCTURE results (fig. S15) recapitulated
    the PCA and worldwide STRUCTURE
    results. However, as K increased, additional population
    clusterswere distinguished (4): theMbugu
    [who speak a mixed Bantu and Cu####ic language
    (30), shown in dark purple]; Cu####ic-speaking
    individuals of southern Ethiopian origin (light
    purple); Nilotic Nilo-Saharan–speaking individuals
    (red); central Sudanic Nilo-Saharan–speaking
    individuals (tan); and Chadic-speaking and
    Baggara individuals (maroon). At K = 14, subtle
    substructure between East African Bantu speakers
    (light orange) andWest CentralAfrican Bantu
    speakers (medium orange), and individuals from
    Nigeria and farther west, who speak various non-
    Bantu Niger-Kordofanian languages (dark orange),
    was also apparent (Fig. 5, B and C). Bantu
    speakers of South Africa (Xhosa, Venda) showed
    substantial levels of the SAK and western
    African Bantu AACs and low levels of the East
    African Bantu AAC (the latter is also present in
    Bantu speakers from Democratic Republic of
    Congo and Rwanda). Our results indicate distinct
    East African Bantu migration into southern
    Africa and are consistent with linguistic and
    archeological evidence of East African Bantu
    migration froman area west of Lake Victoria (28)
    and the incorporation of Khoekhoe ancestry into
    several of the Southeast Bantu populations
    ~1500 to 1000 years ago (31).
    High levels of heterogeneous ancestry (i.e.,
    multiple cluster assignments) were observed in
    nearly all African individuals, with the exception
    of western and central African Niger-Kordofanian
    speakers (medium orange), who are relatively
    homogeneous at large K values (Fig. 5C and fig.
    Fig. 4. Expanded view
    of STRUCTURE results at
    K = 14. Populations from
    the CEPH diversity panel
    are identified by asterisks.
    Languages spoken
    by populations are classified
    as Niger-Kordofanian
    (NK), Nilo-Saharan (NS),
    Afroasiatic (AA), Khoesan
    (KS), or Indo-European (IE).
    www.sciencemag.org SCIENCE VOL 324 22 MAY 2009 1039
    RESEARCH ARTICLE
    Fig. 5. Geographic and genetic structure of populations within Africa. (A) Geographic
    discontinuities among African populations using TESS, assuming a model of no population
    admixture (25). Circles indicate location of populations included in the study. (B) Inferred
    proportions of ancestral clusters from STRUCTURE analysis at K = 14 for individuals grouped
    by geographic region and language classification. Classifications of languages spoken by selfidentified
    ethnic affiliation in the Africans are as in Fig. 1. (C) Inferred proportion of ancestral
    clusters in individuals from STRUCTURE analysis at K = 14.
    1040 22 MAY 2009 VOL 324 SCIENCE www.sciencemag.org
    RESEARCH ARTICLE
    S15). Considerable Niger-Kordofanian ancestry
    (shades of orange) was observed in nearly all populations,
    reflecting the recent spread of Bantu speakers
    across equatorial, eastern, and southern Africa (27)
    and subsequent admixture with local populations
    (28). Many Nilo-Saharan–speaking populations in
    East Africa, such as the Maasai, show multiple
    cluster assignments from the Nilo-Saharan (red) and
    Cu####ic (dark purple) AACs, in accord with
    linguistic evidence of repeated Nilotic assimilation
    of Cu####es over the past 3000 years (32) and with
    the high frequency of a shared East African–specific
    mutation associated with lactose tolerance (33).
    Our data support the hypothesis that the Sahel
    has been a corridor for bidirectional migration
    between eastern and western Africa (34–36). The
    highest proportion of the Nilo-Saharan AAC was
    observed in the southern and central Sudanese
    populations (Nuer, Dinka, Shilluk, and Nyimang),
    with decreasing frequency from northern Kenya
    (e.g., Pokot) to northern Tanzania (Datog, Maasai)
    (Fig. 5, B and C, and fig. S15). Additionally, all
    Nilo-Saharan–speaking populations from Kenya,
    Tanzania, southern Sudan, and Chad clustered
    with west central Afroasiatic Chadic–speaking
    populations in the global analysis at K and#8804; 11 (Fig.
    3), which is consistent with linguistic and
    archeological data suggesting bidirectional migration
    ofNilo-Saharans from source populations
    in Sudan within the past ~10,500 to 3000 years
    (4, 29). The proposed migration of proto-Chadic
    Afroasiatic speakers ~7000 years ago from the
    central Sahara into the Lake Chad Basin may
    have resulted in a Nilo-Saharan to Afroasiatic
    language shift among Chadic speakers (37).
    However, our data suggest that this shift was
    not accompanied by large amounts of Afroasiatic
    gene flow. Other populations of interest, including
    the Fulani (Nigeria and Cameroon), the
    Baggara Arabs (Cameroon), the Koma (Nigeria),
    and Beja (Sudan), are discussed in (4).
    Genetic structure in East Africa. East Africa,
    the hypothesized origin of the migration of
    modern humans out of Africa, has a remarkable
    degree of ethnic and linguistic diversity, as
    reflected by the greatest level of regional substructure
    in Africa (figs. S15, S16, and S19 to
    S21). The diversity among populations from this
    region reflects the proposed long-term presence
    of click-speaking Hadza and Sandawe huntergatherers
    and successive waves of immigration
    of Cu####ic, Nilotic, and Bantu populations
    within the past 5000 years (4, 29, 32, 38, 39).
    Within eastern Africa, including southern and central
    Sudan, clustering is primarily associated with
    language families, including Niger-Kordofanian,
    Afroasiatic, Nilo-Saharan, and two click-speaking
    hunter-gatherer groups: the Sandawe and Hadza
    (figs. S19 to S21). However, individuals from the
    Afroasiatic Cu####ic Iraqw and Gorowa (Fiome)
    and the Nilo-Saharan Datog, who are in close
    geographic proximity, also cluster. Additionally,
    several hunter-gatherer populations were distinct,
    including the Okiek, Akie, and Yaaku and El
    Molo. Of particular interest is the common ancestry
    of the Akie (who have remnants of a
    Cu####ic language) and the Eastern Cu####ic El
    Molo and Yaaku at K = 9, consistent with
    linguistic data suggesting that these populations
    originated from southern Ethiopia and migrated
    into Kenya and Tanzania within the past ~4000
    years (4, 29, 32, 39).
    Origins of hunter-gatherer populations in
    Africa. Our analyses demonstrate potential shared
    ancestry of a number of populations who practice
    (or until recently practiced) a traditional hunting
    and gathering lifestyle. For example, we observed
    a Hadza AAC (yellow) at K = 5 and K = 3
    in the global and African STRUCTURE analyses,
    respectively (Fig. 3 and fig. S15), which is at
    moderate levels (0.18 to 0.32) in the SAK and
    Pygmy populations and at low levels (0.03 to
    0.04) in the Sandawe and neighboring Burunge
    with whom the Sandawe have admixed (tables
    S8 and S9). The SAK and Pygmies continue to
    cluster at higher K values (Fig. 3 and fig. S15)
    and in the TESS (Fig. 5A) and phylogenetic (Fig.
    1) analyses, consistent with an exclusively shared
    Y chromosome lineage (B2b4) (40). Additionally,
    we observed clustering of the SAK, Sandawe,
    and Hadza in the RST phylogenetic tree (fig. S8)
    and of the SAK, Sandawe, and Mbuti Pygmies at
    low K values in the secondary modes of Africa
    STRUCTURE analyses (fig. S16), consistent
    with observed low frequency of the Khoesanspecific
    mitochondrial hap####pe (L0d) in the
    Sandawe (18, 19), the presence of Khoesanrelated
    rock art near the Sandawe homeland (41),
    and similarities between the Sandawe and SAK
    languages (42). These results suggest the possibility
    that the SAK, Hadza, Sandawe, and Pygmy
    populations are remnants of a historically more
    widespread proto–Khoesan-Pygmy population
    of hunter-gatherers. Analyses of mtDNA and Y
    chromosome lineages in the Khoesan-speaking
    populations suggest that divergence may be
    >35,000 years ago (4, 17–19). The shared
    ancestry, identified here, of Khoesan-speaking
    populations with the Pygmies of central Africa
    suggests the possibility that Pygmies, who lost
    their indigenous language, may have originally
    spoken a Khoesan-related language, consistent
    with shared music styles between the SAK and
    Pygmies (4, 43).
    Shared ancestry of western and eastern
    Pygmies, who do not become differentiated until
    larger K values in STRUCTURE analyses (Fig. 3
    and fig. S15), was also supported by the
    phylogenetic trees (Fig. 1 and figs. S7 and S8),
    consistent with mtDNA and autosomal studies
    indicating that the western and eastern Pygmies
    diverged >18,000 years ago (44–47). Western
    Pygmy populations usually clustered (Fig. 3 and
    fig. S15), consistent with a proposed recent
    common ancestry within the past ~3000 years
    (48). However, subtle substructure within the
    western Pygmies was apparent in the analysis
    of central Africa (fig. S24), probably due to
    recent geographic isolation and genetic drift.
    Asymmetric Bantu gene flow into Pygmy populations
    was also observed, with Bantu ancestry
    ranging from 0.13 in Mbuti to 0.54 in the
    Bedzan (table S8), consistent with prior studies
    (40, 44, 49, 50).
    The Hadza, with a census size of ~1000,
    were genetically distinct on a global level with
    STRUCTURE, PCA, and TESS (Figs. 2 to 5),
    consistent with linguistic data indicating that the
    Hadza language is divergent from or unrelated to
    otherKhoesan languages (42, 51, 52). TheHadza,
    who havemaintained a traditional hunter-gatherer
    lifestyle, show low levels of asymmetric gene
    flow from neighboring populations, whereas the
    Sandawe, with a census size of >30,000 (39),
    show evidence of bidirectional gene flow with
    neighboring populations, from whom they may
    have adopted mixed farming technologies (Figs.
    3 to 5 and fig. S15). In fact, we observed high
    levels of the Sandawe AAC in northern Tanzania
    and low levels in northern Kenya and southern
    Ethiopia (Fig. 3 and fig. S15) (K = 8 to 13), consistent
    with linguistic and genetic data suggesting
    that Khoesan populations may once have extended
    from Somalia through eastern Africa and
    into southern Africa (28, 38, 53–55). Although
    the Hadza and Sandawe show evidence of common
    ancestry (Fig. 1 and figs. S7, S8, S14, S18,
    and S21), we observe no evidence of recent gene
    flow between them despite their geographic
    proximity, consistent with mtDNA and Y chromosome
    studies indicating divergence >15,000
    years ago (19). The origins of other African
    hunter-gatherer populations (Dorobo, Okiek,
    Yaaku, Akie, El Molo, and Wata) are discussed
    in (4).
    Origins of human migration within and
    out of Africa. The geographic origin for the
    expansion of modern humans was inferred, as in
    (13), from the correlation between genetic diversity
    and geographic position of populations (r) (figs.
    S30 and S31). Both the point of origin of human
    migration and waypoint for the out-of-Africa
    migration were optimized to fit a linear relationship
    between genetic diversity and geographic distance
    (4). This analysis indicates that modern human
    migration originated in southwestern Africa, at
    12.5°E and 17.5°S, near the coastal border of
    Namibia and Angola, corresponding to the current
    San homeland, with the waypoint in northeast
    Africa at 37.5°E, 22.5°N near the midpoint of the
    Red Sea (figs. S2C, S30, and S31). However, the
    geographic distribution of genetic diversity in
    modern populations may not reflect the distribution
    of those populations in the past, although our
    waypoint analysis is consistent with other studies
    suggesting a northeast African origin of migration
    of modern humans out of Africa (1, 56).
    Correlation between genetic and linguistic
    diversity in Africa. Genetic clustering of populations
    was generally consistent with language
    classification, with some exceptions (Fig. 1 and
    fig. S32). For example, the click-speaking Hadza
    and Sandawe, classified as Khoesan, were separated
    from the SAK populations in the D2 and
    (dm)2 phylogenetic trees (Fig. 1 and fig. S7).
    www.sciencemag.org SCIENCE VOL 324 22 MAY 2009 1041
    RESEARCH ARTICLE
    However, this observation is consistent with
    linguistic studies indicating that these Khoesan
    languages are highly divergent (42, 51) andmay
    reflect gene flow between the Hadza and
    Sandawe with neighboring populations in East
    Africa subsequent to divergence from the SAK.
    Additionally, the Afroasiatic Chadic–speaking
    populations from northern Cameroon cluster
    close to the Nilo-Saharan–speaking populations
    from Chad, rather than with East African Afroasiatic
    speakers (Fig. 1), consistent with a language
    replacement among the Chadic populations.
    Other divergences between genetic and linguistic
    classifications include the Pygmies, who
    lost their indigenous language and adopted the
    neighboring Niger-Kordofanian language (27),
    and the Fulani, who speak aWest African Niger-
    Kordofanian language but cluster near the Chadicand
    Central Sudanic–speaking populations in the
    phylogenies (Fig. 1 and figs. S7 and S8), consistent
    with Y chromosome studies (34). Additionally,
    the Nilo-Saharan–speaking Luo of Kenya
    show predominantly Niger-Kordofanian ancestry
    in the STRUCTURE analyses (orange) (Figs. 3
    and 4, Fig. 5, B and C, and fig. S15) and cluster
    together with eastern African Niger-Kordofanian–
    speaking populations in the phylogenetic trees
    (Fig. 1 and figs. S7 and S8).
    Both language and geography explained a
    significant proportion of the genetic variance, but
    differences exist between and within the language
    families (table S5 and fig. S33, A to C) (4).
    For example, among the Niger-Kordofanian
    speakers, with or without the Pygmies, more of
    the genetic variation is explained by linguistic
    variation (r2 = 0.16 versus 0.11, respectively; P <
    0.0001 for both) than by geographic variation
    (r2 = 0.02 for both; P < 0.0001 for both), consistent
    with recent long-range Bantu migration
    events. The reverse was true for Nilo-Saharan
    speakers (r2 = 0.06 for linguistic distance versus
    0.21 for geographic distance; P < 0.0001 for
    both), possibly due to admixture among Nilo-
    Saharan–, Cu####ic-, and Bantu-speaking populations
    in eastern Africa, which might reduce the
    variation explained by language. The Afroasiatic
    family had the highest r2 for both linguistic and
    geographic distances (0.20 and 0.34, respectively).
    However, when subfamilies were analyzed
    independently, the Chadic-speaking populations
    showed a strong association between geography
    and genetic variation (0.39), but not between
    linguistic and genetic variation (0.0012), as expected
    on the basis of a possible language replacement,
    whereas the Cu####ic-speaking populations
    were significant for both (0.29 and 0.27, respectively)
    (4).
    Genetic ancestry of African Americans and
    CMA populations. In contrast to prior studies
    of African Americans (57–61), we inferred African
    American ancestry with the use of genomewide
    nuclear markers from a large and diverse set
    of African populations. African American populations
    from Chicago, Baltimore, Pittsburgh, and
    North Carolina showed substantial ancestry from
    Fig. 6. Analyses of
    Cape Mixed Ancestry
    (CMA)andAfricanAmerican
    populations. Frequencies
    of inferred
    ancestral clusters are
    shown for K=14with
    the global data set
    for individuals (top
    row) and proportion of
    AACs in self-identified
    populations (bottom
    row). The proportions
    of AACs in the CMA
    and African American
    populations are highlighted
    in the center
    bottom row; proportions
    of AACs in individuals,
    sorted by
    Niger-Kordofanian, European,
    SAK, and/or
    Indian ancestry, are
    shown to the left and
    right, bottom row.
    1042 22 MAY 2009 VOL 324 SCIENCE -20
    RESEARCH ARTICLE
    the African Niger-Kordofanian AAC, most common
    in western Africa (means 0.69 to 0.74), and
    from the European–Middle Eastern AAC (means
    0.11 to 0.15) (Fig. 6 and tables S6 and S8), consistent
    with prior genetic studies and the history of
    the slave trade (4, 57–62). European and African
    ancestry levels varied considerably among individuals
    (Fig. 6). We also detected low levels of
    ancestry fromthe Fulani AAC(means 0.0 to 0.03,
    individual range 0.00 to 0.14), Cu####ic AAC
    (means 0.02, individual range 0.00 to 0.10),
    Sandawe AAC (means 0.01 to 0.03, individual
    range 0.0 to 0.12), East Asian AAC (means 0.01
    to 0.02, individual range 0.0 to 0.08), and Indian
    AAC (means 0.04 to 0.06, individual range 0.01
    to 0.17) (table S6) (4). We observed very low
    levels of Native American ancestry, although
    other U.S. regions may reveal Native American
    ancestry (57).
    Supervised STRUCTURE analysis (fig. S34)
    (4) was used to infer African American ancestry
    from global training populations, including both
    Bantu (Lemande) and non-Bantu (Mandinka)
    Niger-Kordofanian–speaking populations (fig.
    S34 and table S7). These results were generally
    consistent with the unsupervised STRUCTURE
    analysis (table S6) and demonstrate that most
    African Americans have high proportions of both
    Bantu (~0.45mean) and non-Bantu (~0.22mean)
    Niger-Kordofanian ancestry, concordant with
    diasporas originating as far west as Senegambia
    and as far south as Angola and South Africa (62).
    Thus, most African Americans are likely to have
    mixed ancestry from different regions of western
    Africa. This observation, together with the subtle
    substructure observed among Niger-Kordofanian
    speakers, will make it a challenge to trace the
    ancestry of African Americans to specific ethnic
    groups in Africa, unless considerably more
    markers are used.
    The CMA population shows the highest
    levels of intercontinental admixture of any global
    population, with nearly equal high levels of SAK
    ancestry (mean 0.25, individual range 0.01 to
    0.48), Niger-Kordofanian ancestry (mean 0.19,
    individual range 0.01 to 0.71), Indian ancestry
    (mean 0.20, individual range 0.0 to 0.69), and
    European ancestry (mean 0.19, individual range
    0.0 to 0.86) (Fig. 6 and tables S6 and S8). The
    CMA population also has low levels of East
    Asian ancestry (mean 0.08, individual range 0.0
    to 0.21) and Cu####ic ancestry (mean 0.03, individual
    range 0.0 to 0.40). These results are
    consistent with the supervised STRUCTURE
    analyses (fig. S34 and table S7) and with the
    history of the CMA population (4, 63).
    The genetic, linguistic, and geographic landscape
    of Africa. The differentiation observed
    among African populations is likely due to ethnicity,
    language, and geography, as well as technological,
    ecological, and climatic shifts (including
    periods of glaciation and warming) that contributed
    to population size fluctuations, fragmentations,
    and dispersals in Africa (1, 4, 34, 64). We
    observed significant associations between genetic
    and geographic distance in all regions of
    Africa, although their strengths varied. We also
    observed significant associations between genetic
    and linguistic diversity, reflecting the concomitant
    spread of languages, genes, and often
    culture [e.g., the spread of farming during the
    Bantu expansion (28)]. Of interest for future
    anthropological studies are the cases in which
    populations have maintained their culture in the
    face of extensive genetic introgression (e.g.,
    Maasai and Pygmies) and populations that have
    maintained both cultural and genetic distinction
    (e.g., Hadza).
    Given the extensive amount of ethnic diversity
    in Africa, additional sampling—particularly
    from underrepresented regions such as North and
    Central Africa—is important. Because of the
    extensive levels of substructure in Africa, ethnically
    and geographically diverse African populations
    need to be included in resequencing,
    genome-wide association, and pharmacogenetic
    studies to identify population- or region-specific
    functional variants associated with disease or
    drug response (1). The high levels of mixed ancestry
    from genetically divergent ancestral population
    clusters in African populations could also
    be useful for mapping by admixture disequilibrium.
    Future large-scale resequencing and genotyping
    of Africans will be informative for
    reconstructing human evolutionary history, for
    understanding human adaptations, and for identifying
    genetic risk factors (and potential treatments)
    for disease in Africa.
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    samples used in this study. We thank D. Bygott,
    S. J. Deo, D. Guracha, J. Hanby, D. Kariuki, P. Lufungulo,
    A. Mabulla, A. A. Mohamed, W. Ntandu, L. A. Nyindodo,
    C. Plowe, and A. Tibwitta for assisting with sample
    collection; K. Panchapakesan and L. Pfeiffer for
    assistance in sample preparation; S. Dobrin for assistance
    with genotyping; J. Giles, J. Bartlett, N. Kodaman, and
    J. Jarvis for assistance with analyses; and N. Rosenberg,
    J. Pritchard, A. Brooks, J. S. Friedlaender, J. Jarvis,
    C. Lambert, B. Payseur, N. Patterson, and J. Plotkin for
    -23 SCIENCE VOL 324 22 MAY 2009 1043
    RESEARCH ARTICLE
    helpful suggestions and discussions. Conducted in part
    using the ACCRE computing facility at Vanderbilt
    University, Nashville, TN. Supported by L. S. B. Leakey
    and Wenner Gren Foundation grants, NSF grants BCS-
    0196183, BSC-0552486, and BCS-0827436, NIH grants
    R01GM076637 and 1R01GM083606-01, and David and
    Lucile Packard and Burroughs Wellcome Foundation
    Career Awards (S.A.T.); NIH grant F32HG03801 (F.A.R.);
    and NIH grant R01 HL65234 (S.M.W. and J.H.M.).
    Genotyping was supported by the NHLBI Mammalian
    Genotyping Service. The content of this publication does
    not necessarily reflect the views or policies of the
    Department of Health and Human Services, nor does
    mention of trade names, commercial products, or
    organizations imply endorsement by the U.S. government.
    The project included in this manuscript has been funded in
    part with federal funds from the National Cancer Institute
    under contract N01-CO-12400. Original genotype data
    are available at -15
    genetics/genotypingData_Statistics/humanDiversityPanel.
    asp. Data used for analyses in the current manuscript are
    available at -24
    files.html and at -16
    supplementary-data.
    Supporting Online Material
    -25
    Materials and Methods
    SOM Text
    Figs. S1 to S35
    Tables S1 to S9
    References
    13 February 2009; accepted 17 April 2009
    Published online 30 April 2009;
    10.1126/science.1172257
    Include this information when citing this paper.
    REPORTS
    Dispersion of the Excitations of
    Fractional Quantum Hall States
    Igor V. Kukushkin,1,2 Jurgen H. Smet,1* Vito W. Scarola,3,4
    Vladimir Umansky,5 Klaus von Klitzing1
    The rich correlation physics in two-dimensional (2D) electron systems is governed by the dispersion
    of its excitations. In the fractional quantum Hall regime, excitations involve fractionally charged
    quasi particles, which exhibit dispersion minima at large momenta referred to as rotons. These
    rotons are difficult to access with conventional techniques because of the lack of penetration depth
    or sample volume. Our method overcomes the limitations of conventional methods and traces the
    dispersion of excitations across momentum space for buried systems involving small material
    volume. We used surface acoustic waves, launched across the 2D system, to allow incident radiation
    to trigger these excitations at large momenta. Optics probed their resonant absorption. Our
    technique unveils the full dispersion of such excitations of several prominent correlated ground
    states of the 2D electron system, which has so far been inaccessible for experimentation.
    In two-dimensional electron systems (2DESs)
    exposed to a strong perpendicular magnetic
    field B, interaction effects give rise to a
    remarkable set of quantum fluids.When all electrons
    reside in the lowest electronic Landau level,
    the kinetic energy is quenched and the Coulomb
    interaction then dominates. The strong repulsive
    interaction gives rise to the incompressible fractional
    quantum Hall fluids at rational fillings Vp of
    the lowest Landau level of the form vp = p/[2p T
    1], p = 1, 2, 3,… (1). The appearance of these
    fluids may also be understood as a result of
    Landau quantization of a Fermi sea, which forms
    at filling factor vpand#8594;and#8734; = 1/2 and is composed of
    quasi particles referred to as composite fermions
    (2–4). At this filling, these composite fermions
    experience a vanishing effective magnetic field
    Beff. When moving away from half filling, the
    composite fermions are sent into circular cyclotron
    orbits that they execute with frequency wc,CFand#186;
    |Beff|. Landau quantization of these composite
    fermion orbits and the successive depopulation
    of the associated Landau levels give rise to the
    incompressible fractional quantum Hall fluids.
    The lowest energy-neutral excitation of these
    fluids involves a negatively charged quasi particle
    with a fractional charge of e/(2p T 1), where
    e is the charge on the electron (5–7), and a
    positively charged quasi hole that is left behind.
    This excitation requires an energy that, in the
    weakly interacting picture, corresponds to the
    energy gap separating adjacent composite fermion
    Landau levels (4, 8). According to theory,
    these neutral excitations at fractional filling vp
    possess an energy dispersion with p minima at
    large wave vectors q on the order of the inverse
    of the magnetic length lB ¼ pffieffiffi=ffiffihffiffiBffiffiffi, where h
    is Planck’s constant, or about 108 m–1 for typical
    densities of gallium arsenide–based 2DESs
    (1, 9–14).
    The minima are referred to as magneto-roton
    minima and are analogous to the roton minimum
    in the excitation dispersion that was introduced
    by Landau (15) to account for the anomalous
    heat capacity observed in superfluid He-II (16).
    The magneto-roton minima govern the low-
    1Max Planck Institute for Solid State Research, D-70569
    Stuttgart, Germany. 2Institute of Solid State Physics, Russian
    Academy of Science, Chernogolovka 142432, Russia. 3Department
    of Chemistry and Pitzer Center for Theoretical Chemistry,
    University of California at Berkeley, Berkeley, CA 94720, USA.
    4Theoretische Physik, Eidgenand#246;ssische Technische Hochschule
    Zürich, 8093 Zürich, Switzerland. 5Department of Condensed
    Matter Physics, Weizmann Institute of Science, Rehovot 76100,
    Israel.
    *To whom correspondence should be addressed. E-mail:
    -14
    Fig. 1. Experimental arrangement for the detection of resonant microwave absorption at large wave
    vectors. (Left) Sample geometry consisting of a 0.1-mm-wide and 1-mm-long mesa. At its ends, the
    mesa widens and hosts two interdigital transducers with period pSAW. High-frequency radiation drives
    the left transducer. The transducer launches SAWs across the sample. In the active-device region,
    light from a 780-nm laserdiode triggers a luminescence signal. This region of the sample is also
    irradiated with a quasi-monochromatic microwave by using a second high-frequency generator.
    Electrodes 1 and 4, which belong to transducers on opposite sides of the mesa, serve as a dipole
    antenna. (Right) Schematic of the cryostat configuration and the high-frequency chip carrier.
    1044 22 MAY 2009 VOL 324 SCIENCE -26 Muntaser Ibrahim,9 Abdalla T. Juma,9
                  

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          Re: النوبة والنوبا عبد الله شم07-26-14, 09:52 PM
            Re: النوبة والنوبا Bashasha07-27-14, 01:54 AM
              Re: النوبة والنوبا خالد حاكم07-27-14, 02:39 AM
                Re: النوبة والنوبا خالد حاكم07-27-14, 03:05 AM
                Re: النوبة والنوبا cantona_107-27-14, 03:14 PM
              Re: النوبة والنوبا محمد على طه الملك07-27-14, 02:44 AM
              Re: النوبة والنوبا ترهاقا07-27-14, 03:02 AM
                Re: النوبة والنوبا خالد حاكم07-27-14, 03:28 AM
                  Re: النوبة والنوبا Ahmed Alim07-27-14, 05:32 AM
                    Re: النوبة والنوبا Ahmed Alim07-27-14, 05:34 AM
                      Re: النوبة والنوبا Ahmed Alim07-27-14, 05:40 AM
                        Re: النوبة والنوبا Ahmed Alim07-27-14, 05:43 AM
                          Re: النوبة والنوبا Albino Akoon Ibrahim Akoon07-27-14, 12:08 PM
                  Re: النوبة والنوبا Bashasha07-27-14, 11:30 AM
                    Re: النوبة والنوبا Albino Akoon Ibrahim Akoon07-27-14, 12:33 PM
                      Re: النوبة والنوبا بريمة محمد07-27-14, 01:01 PM
                        Re: النوبة والنوبا cantona_107-27-14, 04:36 PM
                      Re: النوبة والنوبا cantona_107-27-14, 04:30 PM
                Re: النوبة والنوبا Elmosley07-28-14, 00:14 AM
  Re: النوبة والنوبا محمد داؤد محمد07-27-14, 04:12 PM
    Re: النوبة والنوبا Albino Akoon Ibrahim Akoon07-27-14, 06:10 PM
      Re: النوبة والنوبا Albino Akoon Ibrahim Akoon07-27-14, 06:31 PM
        Re: النوبة والنوبا Bashasha07-27-14, 06:56 PM
          Re: النوبة والنوبا Ahmed Alim07-27-14, 08:50 PM
            Re: النوبة والنوبا جمال ود القوز07-27-14, 09:15 PM
              Re: النوبة والنوبا Bashasha07-27-14, 10:53 PM
                Re: النوبة والنوبا Bashasha07-27-14, 10:56 PM
                  Re: النوبة والنوبا Bashasha07-27-14, 11:11 PM
                  Re: النوبة والنوبا cantona_107-28-14, 00:05 AM
                    Re: النوبة والنوبا Bashasha07-28-14, 01:17 AM
                      Re: النوبة والنوبا cantona_107-28-14, 02:04 AM
                    Re: النوبة والنوبا احمد حامد صالح07-28-14, 02:00 AM
                      Re: النوبة والنوبا احمد حامد صالح07-28-14, 02:12 AM
                      Re: النوبة والنوبا Bashasha07-28-14, 02:24 AM
                        Re: النوبة والنوبا محمد على طه الملك07-28-14, 02:51 AM
                          Re: النوبة والنوبا Abdalla Teia07-29-14, 09:57 PM
                      Re: النوبة والنوبا السر جميل07-28-14, 05:16 AM
                        Re: النوبة والنوبا احمد حامد صالح07-29-14, 06:29 PM
                          Re: النوبة والنوبا Albino Akoon Ibrahim Akoon07-31-14, 03:19 PM
                            Re: النوبة والنوبا Nasr07-31-14, 05:45 PM
                              Re: النوبة والنوبا خالد حاكم07-31-14, 08:44 PM
                                Re: النوبة والنوبا Abdalla Teia07-31-14, 10:26 PM
                                  Re: النوبة والنوبا cantona_108-01-14, 02:44 AM


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