Chronology and sources of migration Settlement of the Americas

1 chronology , sources of migration

1.1 chronology

1.1.1 archaeological evidence
1.1.2 genomic age estimates


1.2 source populations

1.2.1 human genomic models
1.2.2 htlv-1 genomics
1.2.3 physical anthropology
1.2.4 stemmed points

chronology , sources of migration

while of archaeological community in general agreement americas settled migrants northeastern asian populations, chronology of migrations, source populations contributed migrations, , migration routes remain uncertain. uncertainty fed lack of archaeological evidence along migration routes date periods when migrations proposed have occurred; uncertainties in dating , interpretation of oldest proposed archaeosites in americas; , uncertainties of assumptions underlying chronological , source models of migration derived studies of modern native american genetics.

chronology

map of americas showing pre clovis sites.

in 21st century, models of chronology of migration divided 2 general approaches. first short chronology theory, first migration occurred after last glacial maximum, went decline after 19,000 years ago, , followed successive waves of immigrants. second theory long chronology theory, proposes first group of people entered americas @ earlier date, possibly 21,000–40,000 years ago, followed later second wave of immigrants. further controversy has been generated age-dating of archaeosites in americas , timing of opening of ice-free corridor have challenged clovis first theory, dominated thinking on new world anthropology of 20th century.

archaeological evidence

figure 2. schematic illustration of maternal (mtdna) gene-flow in , out of beringia (long chronology, single source model).



figure 3. illustration of hypothetical chronology migration through beringia (long chronology model). not authoritative on timing of glacial features , not constrained archaeological data.

pre-last glacial maximum migration across beringia americas has been proposed explain purported pre-lgm ages of archaeosites in americas such bluefish caves , old crow flats in yukon territory, , meadowcroft rock shelter in pennsylvania. earlier c date bone artifact @ old crow flats site has been supplanted accelerator mass spectrometry c date indicates holocene age. interpretations of butcher marks , geologic association of bones @ bluefish cave , old crow flats sites have been called question. ages of earliest positively identified artifacts @ meadowcroft site constrained compiled age estimate c in range of 12k-15k c years bp (13.8k-18.5k cal years bp). meadowcroft rockshelter site , monte verde site in southern chile, date of 14.8k cal years bp, archaeosites in americas oldest dates have gained broad acceptance.

stones described probable tools, hammerstones , anvils, have been found in southern california, @ cerutti mastodon site, associated mastodon skeleton appeared have been processed humans. mastodon skeleton dated thorium-230/uranium radiometric analysis, using diffusion–adsorption–decay dating models, 130.7 ± 9.4 thousand years ago. no human bones found, , claims of tools , bone processing have been described not plausible . michael r. waters commented demonstrate such occupation of americas requires presence of unequivocal stone artefacts. there no unequivocal stone tools associated bones... site interesting paleontological locality. chris stringer said extraordinary claims require extraordinary evidence - each aspect requires strongest scrutiny, adding high , concentrated forces must have been required smash thickest mastodon bones, , low energy depositional environment seemingly provides no obvious alternative humans using heavy cobbles found bones.

the yana river rhino horn site (rhs) has dated human occupation of eastern arctic siberia 27k c years bp (31.3k cal years bp). date has been interpreted evidence migration beringia imminent, lending credence occupation of beringia during lgm. however, yana rhs date beginning of cooling period led lgm. but, compilation of archaeosite dates throughout eastern siberia suggest cooling period caused retreat of humans southwards. pre-lgm lithic evidence in siberia indicate settled lifestyle based on local resources, while post-lgm lithic evidence indicate more migratory lifestyle.

the oldest archaeosite on alaskan side of beringia date 12k c years bp (14k cal years bp). possible small founder population had entered beringia before time. however, archaeosites date closer last glacial maximum on either siberian or alaskan side of beringia lacking.

genomic age estimates

recent studies of amerindian genetics have used high resolution analytical techniques applied dna samples modern native americans , asian populations regarded source populations reconstruct development of human y-chromosome dna haplogroups (ydna haplogroups) , human mitochondrial dna haplogroups (mtdna haplogroups) characteristic of native american populations. models of molecular evolution rates used estimate ages @ native american dna lineages branched off parent lineages in asia , deduce ages of demographic events. 1 model based on native american mtdna haplotypes (figure 2) proposes migration beringia occurred between 30k , 25k cal years bp, migration americas occurring around 10k 15k years after isolation of small founding population. model (figure 3) proposes migration beringia occurred approximately 36k cal years bp, followed 20k years of isolation in beringia. yet model proposes migration beringia occurred between 40k , 30k cal years bp, pre-lgm migration americas followed isolation of northern population following closure of ice-free corridor. 3 native american mtdna evolution rate models fall within long chronology theory of migration americas.

a study of diversification of mtdna haplogroups c , d southern siberia , eastern asia, respectively, suggests parent lineage (subhaplogroup d4h) of subhaplogroup d4h3, lineage found among native americans , han chinese, emerged around 20k cal years bp, constraining emergence of d4h3 post-lgm. age estimates based on y-chromosome micro-satellite diversity place origin of american haplogroup q1a3a (y-dna) @ around 10k 15k cal years bp. greater consistency of dna molecular evolution rate models each other , archaeological data may gained use of dated fossil dna calibrate molecular evolution rates.

source populations

there general agreement among anthropologists source populations migration americas originated area somewhere east of yenisei river. common occurrence of mtdna haplogroups a, b, c, , d among eastern asian , native american populations has long been recognized, along presence of haplogroup x. whole, greatest frequency of 4 native american associated haplogroups occurs in altai-baikal region of southern siberia. subclades of c , d closer native american subclades occur among mongolian, amur, japanese, korean, , ainu populations.

human genomic models

the development of high-resolution genomic analysis has provided opportunities further define native american subclades , narrow range of asian subclades may parent or sister subclades. example, broad geographic range of haplogroup x has been interpreted allowing possibility of western eurasian, or european source population native americans, in solutrean hypothesis, or suggesting pre-last glacial maximum migration americas. analysis of ancient variant of haplogroup x among aboriginals of altai region indicates common ancestry european strain rather descent european strain. further division of x subclades has allowed identification of subhaplogroup x2a, regarded specific native americans. further definition of subclades related native american populations, requirements sampling asian populations find closely related subclades grow more specific. subhaplogroups d1 , d4h3 have been regarded native american specific based on absence among large sampling of populations regarded potential descendants of source populations, on wide area of asia. among 3764 samples, sakhalin - lower amur region represented 61 oroks. in study, subhaplogroup d1a has been identified among ulchis of lower amur river region(4 among 87 sampled, or 4.6%), along subhaplogroup c1a (1 among 87, or 1.1%). subhaplogroup c1a regarded close sister clade of native american subhaplogroup c1b. subhaplogroup d1a has been found among ancient jōmon skeletons hokkaido modern ainu regarded descendants of jōmon. occurrence of subhaplogroups d1a , c1a in lower amur region suggests source population region distinct altai-baikal source populations, sampling did not reveal 2 particular subclades. conclusions regarding subhaplogroup d1 indicating potential source populations in lower amur , hokkaido areas stand in contrast single-source migration model.

subhaplogroup d4h3 has been identified among han chinese. subhaplogroup d4h3 china not have same geographic implication subhaplotype d1a amur-hokkaido, implications source models more speculative. parent lineage, subhaplotype d4h, believed have emerged in east asia, rather siberia, around 20k cal years bp. subhaplogroup d4h2, sister clade of d4h3, has been found among jōmon skeletons hokkaido. d4h3 has coastal trace in americas.

the contrast between genetic profiles of hokkaido jōmon skeletons , modern ainu illustrates uncertainty in source models derived modern dna samples:

however, due small sample size or close consanguinity among members of site, frequencies of haplogroups in funadomari skeletons quite different modern populations, including hokkaido ainu, have been regarded direct descendant of hokkaido jomon people.

the descendants of source populations closest relationship genetic profile time when differentiation occurred not obvious. source population models can expected become more robust more results compiled, heritage of modern proxy candidates becomes better understood, , fossil dna in regions of interest found , considered.

htlv-1 genomics

the human t cell lymphotrophic virus 1 (htlv-1) virus transmitted through exchange of bodily fluids , mother child through breast milk. mother-to-child transmission mimics hereditary trait, although such transmission maternal carriers less 100%. htlv virus genome has been mapped, allowing identification of 4 major strains , analysis of antiquity through mutations. highest geographic concentrations of strain hltv-1 in sub-saharan africa , japan. in japan, occurs in highest concentration on kyushu. present among african descendants , native populations in caribbean region , south america. rare in central america , north america. distribution in americas has been regarded due importation slave trade.

the ainu have developed antibodies htlv-1, indicating endemicity ainu , antiquity in japan. subtype has been defined , identified among japanese (including ainu), , among caribbean , south american isolates. subtype b has been identified in japan , india. in 1995, native americans in coastal british columbia found have both subtypes , b. bone marrow specimens andean mummy 1500 years old reported have shown presence of subtype. finding ignited controversy, contention sample dna insufficiently complete conclusion , result reflected modern contamination. however, re-analysis indicated dna sequences consistent with, not from, cosmopolitan clade (subtype a). presence of subtypes , b in americas suggestive of native american source population related ainu ancestors, jōmon.

physical anthropology

paleoamerican skeletons in americas such kennewick man (washington state), hoya negro skeleton (yucatán), luzia woman , other skulls lagoa santa site (brazil), buhl woman (idaho), peñon woman iii, 2 skulls tlapacoya site (mexico city), , 33 skulls baja california have exhibited craniofacial traits distinct modern native americans, leading physical anthropologists opinion paleoamericans of australoid rather siberian origin. basic measured distinguishing trait dolichocephaly of skull. modern isolates such pericúes of baja california , fuegians of tierra del fuego exhibit same morphological trait. other anthropologists advocate alternative hypothesis evolution of original beringian phenotype gave rise distinct morphology similar in known paleoamerican skulls, followed later convergence towards modern native american phenotype. resolution of issue awaits identification of beringian phenotype among paleoamerican skulls or evidence of genetic clustering among examples of australoid phenotype.

a report published in american journal of physical anthropology in january 2015 reviewed craniofacial variation focussing on differences between , late native americans , explanations these based on either skull morphology or molecular genetics. arguments based on molecular genetics have in main, according authors, accepted single migration asia probable pause in berengia, plus later bi-directional gene flow. studies focussing on craniofacial morphology have argued paleoamerican remains have been described closer african , australo-melanesians populations modern series of native americans , suggesting 2 entries americas, 1 occurring before distinctive east asian morphology developed (referred in paper 2 components model . third model, recurrent gene flow [rgf] model, attempts reconcile two, arguing circumarctic gene flow after initial migration account morphological changes. re-evaluates original report on hoya negro skeleton supported rgf model, authors disagreed original conclusion suggested skull shape did not match of modern native americans, arguing skull falls subregion of morphospace occupied both paleoamericans , modern native americans.

stemmed points

stemmed points lithic technology distinct beringian , clovis types. have distribution ranging coastal east asia pacific coast of south america. emergence of stemmed points has been traced korea during upper paleolithic. origin , distribution of stemmed points have been interpreted cultural marker related source population coastal east asia.