Correlation of annual precipitation with human Y-chromosome diversity and the emergence of Neolithic agricultural and pastoral economies in the Fertile Crescent.

Correlation of annual precipitation with human Y-chromosome diversity and the emergence of Neolithic agricultural and pastoral economies in the Fertile Crescent. Introduction The emergence of agriculture in the Fertile Crescent, while acomplex and patchy event, was facilitated by the presence of aMediterranean climate characterised by wet winters and dry summers. Suchhabitats were conducive to natural stands of cereals and legumesgathered by pre-existing sedentary forager populations who were alreadyin place at the onset of the Holocene. Ice ages play an important rolein shaping the genetic history of humans (Hewitt 2000; Torroni et al.1998). The post-glacial warming trend was subsequently interrupted bythe colder, arid Younger Dryas episode, ~11 000-10 300 BP (Bar-Yosef1998; Bellwood 2005). This climatic fluctuation induced a reduction inthe geographic distribution of wild vegetative vegetative/veg��e��ta��tive/ (vej?e-ta?tiv)1. of, pertaining to, or characteristic of plants.2. concerned with growth and nutrition, as opposed to reproduction.3. resources and likelycatalysed cultural change (Twiss 2007) especially under conditions ofdemographic pressure (Bar-Yosef 1998). [FIGURE 1 OMITTED] Genetic patterns in populations are shaped by both locus specificforces (natural selection) and population level forces (drift). Thelatter include migration, founder effect, neutral in situdifferentiation, non-random mating and population size fluctuation(Cavalli-Sforza et al. 1994). Y-chromosome phylogeography most likelyreflects the effects of drift. The topology of the major architecturalbranching structures of human Y-chromosome diversity in the globalbinary phylogeny is an example of common descent with modification(Figure 1). Considerable progress in determining the global phylogenetic phy��lo��ge��net��icadj.1. Of or relating to phylogeny or phylogenetics.2. Relating to or based on evolutionary development or history. framework of the non-recombining haploid haploid/hap��loid/ (hap��loid)1. having half the number of chromosomes characteristically found in the somatic (diploid) cells of an organism; typical of the gametes of a species whose union restores the diploid number. mtDNA genome and Y-chromosomegene trees has propelled the use of these elegant phylogenetic systemsto characterise population structure and reconstruct populationhistories (Underhill & Kivisild 2007). Like climatic andarchaeological evidence, such alternative molecular genetic data alsoinform the multi-disciplinary conversation regarding the transition toagriculture. In the case of the Y-chromosome, each molecular innovation(i.e. a nucleotide substitution, insertion or deletion event) thatcreates a new branch (haplogroup) in the binary gene tree traces to aunique common male molecular ancestor in whom the mutation event firstarose. This fact explains, to a large degree, the observation that thespatial patterning of Y-chromosome diversity often has a particularlystrong correlation with geography (Underhill et al. 2001). One of themajor varieties of Y-chromosomes that occur frequently in the FertileCrescent ate those belonging to haplogroup J, whose representatives allexclusively share a common single derived nucleotide base substitutionthat lies at the root of this haplogroup and defines group membership.Haplogroup J manifests its highest global frequency (~50 per cent) inthe western sector of the Fertile Crescent (Di Giacomo et al. 2004;Semino et al. 2004) with a spread zone spanning from north-west Africa(Arredi et al. 2004) to India (Sengupta et al. 2006). The origin ofhaplogroup J predates the Holocene era and represents a persistent andwidespread deep substrate of ancient common genetic heritage (Cinnioluet al. 2004; Semino et al. 2004). Haplogroup J bifurcates into J1 and J2varieties (Figure 1). The results of several Y-chromosome populationsurveys involving haplogroup J have been reported in populations locatedwithin the general region of the Fertile Crescent. Lifestyle differences exist between agriculturalists andpastoralists (Khazanov 1984). Sedentary agriculturalists andsemi-nomadic herders often occupy different ecological niches (Cauvin2000; Zarins 1990). Dry farming without irrigation irrigation,in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. is confined toregions of [greater than or equal to] 250-400mm of annual precipitation(Bar-Yosef 1998; Buccellati 1992), while pastoral nomadism is anadaptation to regional semi-aridity (Bellwood 2005; Zarins 1990). It hasbeen shown that the spatial variation of rainfall is important indictating the structure of endemic flora (Kadmon & Danin 1999).Since the focus of our study is the Neolithic transition, we restrictour analysis of Y-chromosomes and rainfall to the approximate FertileCrescent 'homeland' region implicated in the shift to anagro-pastoralist economy. We analysed the differential phylogeography ofthe two offsetting sister clades of Y-chromosome haplogroup J todemonstrate the concept of the co-evolution of genes and the phasedorigins of early Neolithic cultivation and herding. Using annualprecipitation to demarcate de��mar��cate?tr.v. de��mar��cat��ed, de��mar��cat��ing, de��mar��cates1. To set the boundaries of; delimit.2. To separate clearly as if by boundaries; distinguish: demarcate categories. arable ([greater than or equal to] 250mm) andsemi-arid landscapes we evaluate corresponding extant Y-chromosome dataas a predictive metric to distinguish between the settled farming andthe domesticated do��mes��ti��cate?tr.v. do��mes��ti��cat��ed, do��mes��ti��cat��ing, do��mes��ti��cates1. To cause to feel comfortable at home; make domestic.2. To adopt or make fit for domestic use or life.3. a. animal herding lifestyles. Methods Twenty-two sets of Haplogroup J frequency data located within theFertile Crescent area were analysed from these current geopoliticallydefined populations: Turkey (Cinniolu et al. 2004); Egypt and Ornan(Luis et al. 2004); Iraq (Semino et al. 2004); Jordan (Flores 2005),Syria and United Arab Emirates United Arab Emirates,federation of sheikhdoms (2005 est. pop. 2,563,000), c.30,000 sq mi (77,700 sq km), SE Arabia, on the Persian Gulf and the Gulf of Oman. (Di Giacomo et al. 2004); Iran (Regueiroet al. 2006); Israeli Bedouins and ethnic Assyrians from Iran, Turkeyand Iraq (unpublished results). Ethnic and linguistic affiliations forsome of these data are available in the original publications. Annual precipitation data were retrieved from The Times Atlas ofthe World The first version of The Times Atlas of the World appeared as The Times Atlas in 1895; more printings followed up to 1900. It was published at the office of The Times newspaper in London, and contained 117 pages of maps with an alphabetical index of 130,000 names. (1989) and the following web resource:http://www.globalbioclimatics.org/form/web.htm. Spatial surfaces ofbinary haplogroup frequency and annual precipitation distributions werecomputed using the MapViewer (version 7, Golden Software, Inc.). A cubicregression analysis using Excel software was performed in which annualprecipitation was the independent variable used to predict the frequencyof Y haplogroups J1-M267, J2aM410 and J2b-M12. The cubic regressionanalysis was chosen in order to detect maximal, minimal and inflectionalpoints in the data set. In addition Spearman ranked correlations werecalculated to test significance of the relationships betweenprecipitation and each Y-chromosome haplogroup frequency using the SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance. 11.0 computational statistics application. Results As predicted, both haplogroups J1 and J2a correlated significantlywith annual precipitation. The Spearman correlation tests gave thefollowing results for each haplogroup: J1 r = -0.45, p<0.05; J2a r =0.56, p<0.01; and J2b r = 0.00, p (not significant). The cubicregression for haplogroups J1 and J2a were also significant, F(3,18) =8.47 p <0.001 and F(3,18) = 8.22, p < 0.0012 respectively. Figure2 illustrates the cubic fit of haplogroups J1 and J2a versus annualprecipitation. As shown, haplogroup J1 frequency increases asprecipitation level reduces below the 400mm per year threshold, typicalof semi-arid climates. In contrast, haplogroup J2a frequency reaches amaximum at 700mm per year within the Mediterranean woodland and openparkland zone (Bar-Yosef 1998). Figure 3 displays the sample sites,precipitation contours and the interpolated haplogroup frequencycontours in the geographic regions analysed. Again, haplogroup J2afrequency closely tracks the higher rainfall regions, while haplogroup J1 distributes in the semi-arid and desert regions. [FIGURE 2 OMITTED] Discussion Climatic fluctuation can spur movements of humans and also act as amechanism triggering social change (Kuper & Kropelin 2006).Development of Neolithic agro-pastoral economies enhanced theopportunity for more rapid cultural divergence. It is plausible thatpastoral nomadism was an adaptation to the general semi-aridity of theregion that allowed peoples to extend their territorial range (Cauvin2000). Although seasonality affects both agriculturalists andpastoralists, its influence differs through the cultivation cycle versusthe mobility cycle, respectively. The study of Neolithic nomads isdifficult since it leaves fewer indications in the archaeologicalrecord. Nonetheless, some evidence of early (8000-7600 BP) nomadicherding preserved by sandstorms has been reported in semi-arid zones inthe southern Levant Levant(ləvănt`)[Ital.,=east], collective name for the countries of the eastern shore of the Mediterranean from Egypt to, and including, Turkey. (Cauvin 2000; Zarins 1990). Previously it was shown that the cline of haplogroup J2 frequencypredicted with over 80 per cent accuracy the distributions of bothNeolithic pottery and figurines in the Near East and south-easternEurope (King & Underhill 2002). This analysis provides anotherexample of the correlation of Y-chromosomes and the Neolithic from alifestyle perspective. The genetic memory retained in the extantdistributions of Y-chromosome haplogroups J1-M267 and J2a-M410 withinthe Fertile Crescent significantly correlates with regional levels ofannual precipitation in a reciprocal manner. The statisticallysignificant correlations of Y-chromosome haplogroups, precipitationlevels and domestic lifestyle ate pronounced. The spatial frequencydistribution of haplogroup J2a coincides closely with regionscharacterised by [greater than or equal to] 400mm of annualprecipitation capable of supporting settled agriculture, whilehaplogroup J1-M267 distributions correlate inversely with semi-aridregions characteristically used by pastoralists. The frequency distributions for both haplogroups overlap whenannual precipitation approximates 250mm (Figure 2). This climatictransition zone (Buccellati 1992) underscores the importance of notdirectly conflating haplogroup type with ethnicity. While the respectivehaplogroup distributions are not mutually exclusive, in general, therespective differentials in the opposing lifestyle and precipitationzones is undeniable. Prior work on the geographic origin and theestimated dates for the temporal expansion of lineages J 1M267 andJ2a-M410 suggest a common origin near the Upper Euphrates in thefoothills of the Taurus mountains dating to the Late Glacial Maximum(LGM LGM Last Glacial MaximumLGM Little Green Men (Astronomical: first used as the designation for pulsars)LGM Lembaga Getah Malaysia (Malay: Malaysian Rubber Board)LGM The Lone Gunmen ) (Cinniolu et al. 2004; Semino et al. 2004). A probable scenario isthat after the onset of the Holocene during the PPNB PPNB Pre-Pottery Neolithic B (era)period both J1-M267and J2a-M410 participated in the shift to an agro-pastoral economy withsome J1-M267 lineages occupying the semi-arid regions in the Arabianpeninsula adjacent to the Fertile Crescent. At that time, an increase infrequency of J1M267 among semi-nomadic population was likely a randomfluctuation in gene frequencies. However, continued social-culturalbarriers to population flow such as endogamy endogamy(ĕndŏg`əmē): see marriage. and patrilocality pat��ri��lo��cal?adj. AnthropologyOf or relating to residence with a husband's kin group or clan.pat couldhave led to the observed current differential geographic frequenciesbetween the J2a-M410 and J1-M267 haplogroups. The preference forintermediate annual rainfall levels (400-800mm) among Early Neolithicsettlements may have also extended to Thessaly in Greece (Perles 2001)where J2a-M410 has been observed at high frequency (Di Giacomo et al.2003). [FIGURE 3 OMITTED] This study also provides a framework for the analysis of thematernally inherited mitochondrial DNA genome (mtDNA) and rainfall inthe Fertile Crescent. The mtDNA genome is sensitive to both naturalselection (Kivisild et al. 2006) and sex-specific forces at thepopulation level and may provide insights into possible sex-bias(Underhill & Kivisild 2007). We acknowledge that our simple dichotomous di��chot��o��mous?adj.1. Divided or dividing into two parts or classifications.2. Characterized by dichotomy.di��chot model does not recordthat early Neolithic societies were complex entities often characterisedby broad spectrum and nuanced subsistence strategies (Twiss 2007) thatate not necessarily recorded in the genes. Complexity in paternalheritage exists in most populations beyond just one haplogroup varietyof Y-chromosomes participating in a range expansion byagro-pastoralists. Nevertheless the pattern of J1 and J2 haplogroupmapping provides a suggestive signal of dispersion. Acknowledgements The authors wish to thank Professors L. Luca Cavalli-Sfzora andAaron Brody for their valuable comments as well as comments by twoanonymous referees. We thank Francesca Lattanzi, Mahnoosh Nik-Ahd andJabeen Ahmad for the Assyrian data. Received 20 August 2007; Accepted: 10 October 2007; Revised: 23October 2007 References ARREDI, B., E.S. POLONI, S. 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Jacques Chiaroni, French Blood Establishment of Alpes Mediterranee(EFSAM), 149 Boulevard Baille, 13005 Marseille, France and UMR UMR Unite Mixte de Recherche (French: Mixed Unit of Research )UMR University of Missouri - RollaUMR Upper Mississippi RiverUMR Uniform Methods and Rules (US Department of Agriculture)UMR Unit Manning Report 6578(CNRS/Faculty of Medicine of Marseille) Biological and CulturalAdaptability, Faculty of Medicine, Marseille, France Roy J. King, Department of Psychiatry and Behavioral Sciences, 401Quarry Road, Stanford University, Stanford, CA 943055722, USA Peter A. Underhill, Department of Genetics, Stanford UniversitySchool of Medicine Stanford University School of Medicine is affiliated with Stanford University and is located at Stanford University Medical Center in Stanford, California, adjacent to Palo Alto and Menlo Park. , 300 Pasteur Drive, Stanford, CA 94305-5120, USA