Originea africană recentă a oamenilor moderni: Diferență între versiuni

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==Exodul din Africa==
==Exodul din Africa==
[[Image:Red Sea2.png|thumb|right|200px|[[Red Sea]] crossing]]
Some 70 millennia ago, a part of the bearers of mitochondrial haplogroup
[[Haplogroup L3 (mtDNA)|L3]] migrated from [[East Africa]] into the [[Near East]].

Some scientists believe that only a few people left Africa in a single migration that went on to populate the rest of the world,<ref>{{cite web|url=http://news.softpedia.com/news/Both-Aborigines-and-Europeans-Rooted-in-Africa-54225.shtml |title=Both Australian Aborigines and Europeans Rooted in Africa |publisher=News.softpedia.com |date= |accessdate=2011-01-11}}</ref> based in the fact that only descents of [[Haplogroup L3 (mtDNA)|L3]] are found outside Africa. From that settlement, some others point to the possibility of several waves of expansion. For example, [[Spencer Wells|Wells]] says that the early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea, and colonized Australia by around 50,000 years ago. The [[Australian Aborigines|Aborigines of Australia]], Wells says, are the descendants of the first wave of migrations.<ref>{{cite news |url= http://news.bbc.co.uk/2/hi/science/nature/7358868.stm |title= Human line 'nearly split in two' |publisher= BBC News |date= April 24, 2008 | accessdate=2009-12-31 | first=Paul | last=Rincon}}</ref>

It has been estimated that from a population of 2,000 to 5,000 in Africa, only a small group of possibly 150 people crossed the Red Sea. This is because, of all the lineages present in Africa, only the daughters of one lineage, L3, are found outside Africa. Had there been several migrations one would expect more than one African lineage outside Africa. L3's daughters, the M and N lineages, are found in very low frequencies in Africa (although haplogroup M1 is very ancient and diversified in [[North Africa|North]] and [[Horn of Africa|Northeast Africa]]) and appear to be recent arrivals. A possible explanation is that these mutations occurred in East Africa shortly before the exodus and by the [[founder effect]] became the dominant haplogroups after the exodus from Africa. Alternatively, the mutations may have arisen shortly after the exodus from Africa.

Other scientists have proposed a Multiple Dispersal Model, in which there were two migrations out of Africa, one across the Red Sea travelling along the coastal regions to [[South Asia|India]] (the Coastal Route), which would be represented by Haplogroup M. Another group of migrants with Haplogroup N followed the Nile from East Africa, heading northwards and crossing into [[Asia]] through the [[Sinai]]. This group then branched in several directions, some moving into Europe and others heading east into Asia. This hypothesis attempts to explain why Haplogroup N is predominant in Europe and why Haplogroup M is absent in Europe. Evidence of the coastal migration is hypothesized to have been destroyed by the rise in sea levels during the [[Holocene]] epoch.<ref>{{cite web|url=http://www.biomedcentral.com/1471-2156/2/13/comments/comments |title=A single origin, several dispersal hypothesis |publisher=Biomedcentral.com |date=2004-10-29 |accessdate=2011-01-11}}</ref><ref>[http://www.human-evol.cam.ac.uk/Projects/sdispersal/sdispersal.htm Searching for traces of the Southern Dispersal], by Dr. Marta Mirazón Lahr, et al.</ref> Alternatively, a small European founder population that initially expressed both Haplogroup M and N could have lost Haplogroup M through random genetic drift resulting from a [[Population bottleneck|bottleneck]] (i.e. a [[founder effect]]).

Today at the [[Bab-el-Mandeb straits]] the [[Red Sea]] is about 12 miles (20 kilometres) wide, but 50,000 years ago it was much narrower and sea levels were 70 meters lower. Though the straits were never completely closed, there may have been islands in between which could be reached using simple rafts. Shell [[middens]] 125,000 years old have been found in [[Eritrea]],<ref name="pmid10811218">{{cite journal | author = Walter RC, Buffler RT, Bruggemann JH, Guillaume MM, Berhe SM, Negassi B, Libsekal Y, Cheng H, Edwards RL, von Cosel R, Néraudeau D, Gagnon M | title = Early human occupation of the Red Sea coast of Eritrea during the last interglacial | journal = Nature | volume = 405 | issue = 6782 | pages = 65–9 | year = 2000 | month = May | pmid = 10811218 | doi = 10.1038/35011048 | ref = harv }}</ref> indicating the diet of early humans included seafood obtained by [[beachcombing]].


==Extinderea ulterioară==
==Extinderea ulterioară==
[[File:Spreading homo sapiens.jpg|thumb|320px|Map of [[early human migrations]]<ref>Literature: Göran Burenhult: Die ersten Menschen, Weltbild Verlag, 2000. ISBN 3-8289-0741-5</ref>]]
From the Near East, these populations spread east to [[Paleolithic South Asia|South Asia]] by 50,000 years ago, and on to [[Prehistoric Australia|Australia]] by 40,000 years ago, ''Homo sapiens'' for the first time colonizing territory never reached by ''Homo erectus''. [[Paleolithic Europe|Europe]] was reached by [[Cro-Magnon]] some 40,000 years ago. East Asia ([[Prehistoric Korea|Korea]], [[Japanese Paleolithic|Japan]]) was reached by 30,000 years ago. It is disputed whether subsequent [[Models of migration to the New World|migration to North America]] took place around 30,000 years ago, or only considerably later, around 14,000 years ago.

The group that crossed the Red Sea travelled along the coastal route around the coast of [[Arabia]] and [[Persia]] until reaching India, which appears to be the first major settling point. M is found in high frequencies along the southern coastal regions of [[Pakistan]] and India and it has the greatest diversity in India, indicating that it is here where the mutation may have occurred.<ref name="pmid15339343">{{cite journal | author = Metspalu M, Kivisild T, Metspalu E, Parik J, Hudjashov G, Kaldma K, Serk P, Karmin M, Behar DM, Gilbert MT, Endicott P, Mastana S, Papiha SS, Skorecki K, Torroni A, Villems R | title = Most of the extant mtDNA boundaries in south and southwest Asia were likely shaped during the initial settlement of Eurasia by anatomically modern humans | journal = BMC Genet. | volume = 5 | issue = | page = 26 | year = 2004 | month = August | pmid = 15339343 | pmc = 516768 | doi = 10.1186/1471-2156-5-26 | ref = harv }}</ref> Sixty percent of the Indian population belong to Haplogroup M. The indigenous people of the [[Andaman Islands]] also belong to the M lineage. The Andamanese are thought to be offshoots of some of the earliest inhabitants in Asia because of their long isolation from mainland Asia. They are evidence of the coastal route of early settlers that extends from India along the coasts of [[Thailand]] and Indonesia all the way to [[Papua New Guinea]]. Since M is found in high frequencies in highlanders from New Guinea as well, and both the Andamanese and New Guineans have dark skin and [[natural hair|Afro-textured hair]], some scientists believe they are all part of the same wave of migrants who departed across the Red Sea ~60,000 years ago in the [[Great Coastal Migration]]. Notably, the findings of Harding et al. (2000, p.&nbsp;1355) show that, at least with regard to dark [[skin color]], the haplotype background of Papua New Guineans at [[MC1R]] (one of a number of genes involved in melanin production) is identical to that of Africans (barring a single silent mutation). Thus, although these groups are distinct from Africans at other loci (due to drift, bottlenecks, etc), it is evident that selection for the dark [[skin color]] trait likely continued (at least at MC1R) following the exodus. This would support the hypothesis that suggests that the original migrants from Africa resembled pre-exodus Africans (at least in skin color), and that the present day remnants of this ancient phenotype can be seen among contemporary Africans, Andamanese and New Guineans. Others suggest that their physical resemblance to Africans could be the result of [[convergent evolution]].<ref>{{cite web|url=http://ehl.santafe.edu/ruhlen.htm |title=Evolution of Human Languages |publisher=Ehl.santafe.edu |date= |accessdate=2011-01-11}}</ref><ref name="pmid12478481">{{cite journal | author = Endicott P, Gilbert MT, Stringer C, Lalueza-Fox C, Willerslev E, Hansen AJ, Cooper A | title = The genetic origins of the Andaman Islanders | journal = Am. J. Hum. Genet. | volume = 72 | issue = 1 | pages = 178–84 | year = 2003 | month = January | pmid = 12478481 | pmc = 378623 | doi = 10.1086/345487 | url = | issn = }}</ref>

From [[Arabia]] to India the proportion of haplogroup M increases eastwards: in eastern India, M outnumbers N by a ratio of 3:1. However, crossing over into East Asia, Haplogroup N reappears as the dominant lineage. M is predominant in South East Asia but amongst [[Indigenous Australians]] N reemerges as the more common lineage. This discontinuous distribution of Haplogroup N from Europe to Australia can be explained by [[founder effect]]s and [[population bottleneck]]s.<ref name="pmid12840039">{{cite journal | author = Ingman M, Gyllensten U | title = Mitochondrial genome variation and evolutionary history of Australian and New Guinean aborigines | journal = Genome Res. | volume = 13 | issue = 7 | pages = 1600–6 | year = 2003 | month = July | pmid = 12840039 | pmc = 403733 | doi = 10.1101/gr.686603 | ref = harv }}</ref>


==Ipoteze alternative==
==Ipoteze alternative==
The multiregional hypothesis, initially proposed by Milford Wolpoff, holds that the evolution of humans from ''H. erectus'' at the beginning of the [[Pleistocene]] 1.8 million years BP to the present day has been within a single, continuous worldwide population. Proponents of multiregional origin reject the assumption of an [[species barrier|infertility barrier]] between ancient Eurasian and African populations of ''Homo''. Multiregional proponents point to the fossil record and [[Multiregional origin of modern humans#Genetic evidence|genetic evidence]] in chromosomal DNA. One study suggested that at least 5% of the human modern gene pool can be attributed to ancient admixture, which in Europe would be from the [[Neanderthal]]s.<ref name="Plagnol">{{cite journal | author = Plagnol V, Wall JD | title = Possible ancestral structure in human populations | journal = PLoS Genet. | volume = 2 | issue = 7 | pages = e105 | year = 2006 | month = July | pmid = 16895447 | pmc = 1523253 | doi = 10.1371/journal.pgen.0020105 | quote = ..strong evidence for ancient admixture in both a European and a West African population (p ≈ 10−7), with contributions to the modern gene pool of at least 5%. While Neanderthals form an obvious archaic source population candidate in Europe.. | ref = harv }}</ref>

A recently discovered fossilized mandible that is putatively a hybrid between ''Homo sapiens'' and an earlier hominid, that is likely to be 110,000 years old, has been interpreted as a challenge to the recent out-of-Africa hypothesis. However, some scholars doubt that the fossil represents a Homo sapiens hybrid.<ref name="urlChinese challenge to out of Africa theory - life - 03 November 2009 - New Scientist">{{cite web | url = http://www.newscientist.com/article/dn18093-chinese-challenge-to-out-of-africa-theory.html | title = Chinese challenge to 'out of Africa' theory - life - 03 November 2009 - | author = McKenna P | authorlink = | coauthors = | date = 2009-11-03 | work = | publisher = New Scientist | pages = | language = | archiveurl = | archivedate = | quote = | accessdate = }}</ref>


==Referințe==
==Referințe==

Versiunea de la 17 ianuarie 2011 15:48

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Fișier:Migration map4.png
Harta migrațiilor umane dedusă după distribuția haplogrupelor mitocondriale.

Originea africană recentă a oamenilor moderni este în paleoantropologie modelul principal care descrie originea și dispersarea timpurie a omului modern anatomic. Teoria este adesea numită în presa populară modelul „Out of Africa” (nume ce face referință la filmul american Out of Africa, realizat de Sydney Pollack din 1985 după romanului autobiografic Ferma africană al scriitoarei daneze Karen Blixen) și este cunoscută în mediul universitar ca ipoteza originii unice recente (recent single-origin hypothesis), ipoteza înlocuirii (replacement hypothesis) și modelul originii africane recente (recent African origin model). Ipoteza ce presupune că oamenii au o singură origine (monogeneza) a fost publicată de Charles Darwin în Descendența omului (1871).

Conceptul a fost speculativ până în anii 1980, când a fost confirmat de studiul ADN-ului mitocondrial al indivizilor trăind în zilele noastre, coroborat cu dovezi bazate pe antropologia fizică a speciilor arhaice. Conform dovezilor genetice și paleontologice, Homo sapiens arhaic a evoluat către omul modern anatomic numai în Africa, între 200.000 și 100.000 de ani în urmă, o ramură a acestei populații părăsind Africa acum aproximativ 60.000 de ani și, în timp, înlocuind populațiile anterioare de hominide, cum ar fi Homo neanderthalensis și Homo erectus. Originea recentă unică a omului modern în Africa de Est este poziția consensuală general acceptată de comunitatea științifică.[1][2][3][4][5]

Cu toate acestea, secvențierea completă recentă a genomului omului de Neanderthal sugerează că neandertalienii și unii oameni moderni împărtășesc un fond genetic comun ancestral. Autorii studiului sugerează că descoperirile lor sunt compatibile cu prezența, în unele populații, de până la 4% din genomul neandertalienilor. De asemenea, studiul sugerează că pot exista și alte motive pentru care oamenii și neanderthalienii împărtășesc un fond genetic comun.[6][7] Ipoteza concurentă este cea a originii multiregionale a oamenilor moderni. Cercetători ce susțin această ipoteză consideră că migrația originală Out of Africa a fost cu mult mai precoce, la două milioane de ani în urmă, și că în acest caz cel care a migrat a fost Homo erectus și nu Homo sapiens. [4][8]

Istoria teoriei

Odată cu dezvoltarea antropologiei în secolul al XIX-lea, dezacorduri au apărut între oamenii de știință cu privire la diferitele teorii referitoare la evoluția umană. În timp ce unii dintre aceștia, cum ar fi Johann Friedrich Blumenbach și James Cowles Pritchard, apreciau că diferitele rase umane sunt varietăți ce au o ascendență comună, adversarii lor, cum ar fi Louis Agassiz și Josiah C. Nott, susțineau poligenismul, fie ca o dezvoltare separată a raselor umane ca specii diferite, fie ca o dezvoltare de specii distincte prin evoluția unor specii de maimuțe, fără nici un strămoș comun.

Charles Darwin a fost printre primii care a propus o descendență comună a organismelor vii și care a sugerat că toți oamenii au strămoși comuni care au trăit în Africa. În cartea Descendența Omului (Descent of Man), el a emis ipoteza că oamenii se trag din maimuțe ce aveau încă un creier mic, dar care se deplasau în poziție verticală, eliberându-și astfel mâinile pentru utilizări ce au favorizat dezvoltarea inteligenței. Mai mult, el era convins că aceste maimuțe au trăit în Africa:[9]

„In each great region of the world the living mammals are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere. But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale.”
—Charles Darwin, Descent of Man[10]

Prezicerea sa a fost perspicace, deoarece la acel moment, în 1871, nu existau practic fosile disponibile aparținând vechilor hominizii. Aproape cincizeci de ani mai târziu, ipoteza lui Darwin a fost confirmată atunci când antropologii au început să descopere în mai multe zone din Africa numeroase fosile de hominizi cu creier mic. Concepțiile din antropologie au pivotat pe la mijlocul secolului 20 în favoarea monogenismului. Totuși, susținători izolați ai poligenismului au mai existat și după mijlocul secolul 20, cum ar fi Carleton Coon, care a emis în 1962 ipoteza că specia Homo sapiens ar fi evoluat din Homo erectus în cinci locuri separate în cinci momente diferite. [11] „Originea africană recentă” a omului modern înseamnă „origine unică” (monogenism) și a fost folosit, în diverse contexte, ca antonim al termenului de poligenism.

Odată cu apariția arheogeneticii în anii 1990, oamenii de știință au reușit să dateze migrația „Out of Africa” cu o anumită precizie. În anul 2000, secvența ADN-ul mitocondrial (ADNmt) al fosilei „Omul din Mungo” (Mungo Man) din Australia a fost publicată.[12] Aceste rezultate, ce au fost ulterior puse la îndoială[13] au fost însă suținute de către W. James Peacock, șeful echipei care a secvențiat ADN-ul mitocondrial al „Omului din Mungo”. [14][nefuncțională]

Întrebarea dacă există o moștenire în fondul genetic al Homo sapiens provenind de la alte subspecii tipologice (nu de facto) de Homo este încă dezbătută.

Homo sapiens arhaic

Omul modern din punct de vedere anatomic își are originea în Africa aproximativ 250.000 de ani în urmă. Tendința la mărirea volumului cranian și elaborarea de unelte de piatră (tehnologia acheuleană) care au avut loc între aproximativ 400.000 de ani în urmă și a doua perioadă interglaciare în Pleistocenului Mijlociu (aproximativ 250.000 de ani în urmă) oferă dovezi în favoarea unei tranziții de la H. erectus la H. sapiens. [Citare ] Conform modelului originii africane recente, migrația în interiorul și în afara Africii a înlocuit în cele din urmă populațiile de H. erectus dispersate anterior.

Homo sapiens idaltu, ale cărui fosile au fost găsit la Middle Awash din Etiopia, a trăit acum aproximativ 160.000 de ani.[15] Este cel mai vechi om modern din punct de vedere anatomic cunoscut și este clasificat ca o subspecie disparută.[16] Fosile aparținând lui Homo sapiens timpuriu au fost găsite în peștera Qafzeh din Israel și au fost datate la aproximativ 80.000 - 100.000 de ani în urmă. Cu toate acestea, acești oameni fie că au dispărut ori s-au retras spre Africa acum 70.000 - 80.000 de ani în urmă, fie au fost înlocuiți de oamenii de Neanderthal ce s-au refugiat spre sud părăsind regiunile reci ale Europei în timpul epocii glaciare [necesită citare]. Hua Liu et al., analizând markeri microsateliți autozomali, datează la aproximativ 56.000 ± 5.700 ani în urmă ADN-ul mitocondrial fosil (de verificat în articol căci markeri autozomali și ADNmt !). Ei interpretează fosilele omului modern timpuriu din peștera Qafzeh ca o ramură timpurie izolată, care ulterior s-a retras înapoi în Africa.[1]

Toate celelalte fosile de om modern găsite în afara Africii au fost datate la perioade mai recente. Cele mai vechi fosile bine datate găsite în afara Africii sunt cele de la Lacul Mungo (Lake Mungo), Australia, ce au fost datate la aproximativ 42.000 ani în urmă. [17][18] Fosilele din peștera Tianyuan din regiunea Liujiang (China) sunt datate în perioada 38.000 și 42.000 de ani în urmă de unii cercetători. Ele sunt cele mai similare din punct de vedere morfologic cu omul fosil din Minatogawa (Minatogawa Man) descoperit pe insula Okinawa din Japonia, om modern din punct de vedere anatomic ale cărui fosile au fost datate între 17.000 și 19.000 de ani în urmă.[19][20]

Ipoteza răspândirii tardive în afara Africii a omului anatomic modern este contrazisă de rezulatele obținute de un alt grup de cercetători care datează fosilele omului din Liujang la aproximativ 111.000 - 139.000 ani în urmă. [21]

Începând cu aproximativ 100.000 de ani încep să apară dovezi ce demonstrează o tehnologie sofisticată și prezența preocupărilor artistice, iar cu 50.000 de ani în urmă comportamentul modern al speciei umane devine evident. Instrumentele de piatră arată prezența de modele care sunt reproduse sau duplicate cu mai multă precizie, în timp ce instrumentele din os și corn de cerb își fac apariția pentru prima dată.[22][23]

Reconstrucția genetică

Two pieces of the human genome are quite useful in deciphering human history: mitochondrial DNA and the Y chromosome. These are the only two parts of the genome that are not shuffled about by the evolutionary mechanisms that generate diversity with each generation: instead, these elements are passed down intact. According to the hypothesis, all people alive today have inherited the same Mitochondria[24] from one woman who lived in Africa about 160,000 years ago[25][26] she has been named Mitochondrial Eve. All men today have inherited their Y chromosomes from a man who lived 60,000 years ago, probably in Africa. He has been named Y-chromosomal Adam. It is now believed that more men participated in the out of Africa exodus of early humans than women based on comparing non-sex-specific chromosomes with sex-specific ones.[27]

Mitochondrial DNA

Articol principal: Human mitochondrial DNA haplogroup.
One model of human migration based on Mitochondrial DNA

The first lineage to branch off from Mitochondrial Eve is L0. This haplogroup is found in high proportions among the San of Southern Africa, the Sandawe of East Africa. It is also found among the Mbuti people.[28][29]

These groups branched off early in human history and have remained relatively genetically isolated since then. Haplogroups L1, L2 and L3 are descendents of L1-6 and are largely confined to Africa. The macro haplogroups M and N, which are the lineages of the rest of the world outside Africa, descend from L3.

Y-chromosomal DNA

Articole principale: Human Y-chromosome DNA haplogroups, Haplogroup CT (Y-DNA) și Haplogroup F (Y-DNA).

The mutations defining macro-haplogroup CT (all Y haplogroups except A and B) predate the "Out of Africa" migration, its descendent macro-group DE being confined to Africa. The mutations that distinguish Haplogroup C from all other descendants of CR have occurred some 60,000 years ago, shortly after the first Out of Africa migration.

Haplogroup F originated some 45,000 years ago, either in North Africa (in which case it would point to a second wave of out-of-Africa migration) or in South Asia. More than 90% of males not native to Africa are descended in direct male line from the first bearer of haplogroup F.

Genomic analysis

Although mitochondrial DNA and Y-chromosomal DNA are particularly useful in deciphering human history, data on the genomes of dozens of population groups have also been studied. In June 2009, an analysis of genome-wide SNP data from the International HapMap Project (Phase II) and CEPH Human Genome Diversity Panel samples was published.[30] Those samples were taken from 1138 unrelated individuals.[30] Before this analysis, population geneticists expected to find dramatic differences among ethnic groups, with derived alleles shared among such groups but uncommon or nonexistent in other groups.[31] Instead the study of 53 populations taken from the HapMap and CEPH data revealed that the population groups studied fell into just three genetic groups: Africans, Eurasians (which includes natives of Europe and the Middle East, and Southwest Asians east to present-day Pakistan), and East Asians, which includes natives of Asia, Japan, Southeast Asia, the Americas, and Oceania.[31] The study determined that most ethnic group differences can be attributed to genetic drift, with modern African populations having greater genetic diversity than the other two genetic groups, and modern Eurasians somewhat more than modern East Asians.[31] The study suggested that natural selection may shape the human genome much more slowly than previously thought, with factors such as migration within and among continents more heavily influencing the distribution of genetic variations.[32]

Exodul din Africa

Red Sea crossing

Some 70 millennia ago, a part of the bearers of mitochondrial haplogroup L3 migrated from East Africa into the Near East.

Some scientists believe that only a few people left Africa in a single migration that went on to populate the rest of the world,[33] based in the fact that only descents of L3 are found outside Africa. From that settlement, some others point to the possibility of several waves of expansion. For example, Wells says that the early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migrations.[34]

It has been estimated that from a population of 2,000 to 5,000 in Africa, only a small group of possibly 150 people crossed the Red Sea. This is because, of all the lineages present in Africa, only the daughters of one lineage, L3, are found outside Africa. Had there been several migrations one would expect more than one African lineage outside Africa. L3's daughters, the M and N lineages, are found in very low frequencies in Africa (although haplogroup M1 is very ancient and diversified in North and Northeast Africa) and appear to be recent arrivals. A possible explanation is that these mutations occurred in East Africa shortly before the exodus and by the founder effect became the dominant haplogroups after the exodus from Africa. Alternatively, the mutations may have arisen shortly after the exodus from Africa.

Other scientists have proposed a Multiple Dispersal Model, in which there were two migrations out of Africa, one across the Red Sea travelling along the coastal regions to India (the Coastal Route), which would be represented by Haplogroup M. Another group of migrants with Haplogroup N followed the Nile from East Africa, heading northwards and crossing into Asia through the Sinai. This group then branched in several directions, some moving into Europe and others heading east into Asia. This hypothesis attempts to explain why Haplogroup N is predominant in Europe and why Haplogroup M is absent in Europe. Evidence of the coastal migration is hypothesized to have been destroyed by the rise in sea levels during the Holocene epoch.[35][36] Alternatively, a small European founder population that initially expressed both Haplogroup M and N could have lost Haplogroup M through random genetic drift resulting from a bottleneck (i.e. a founder effect).

Today at the Bab-el-Mandeb straits the Red Sea is about 12 miles (20 kilometres) wide, but 50,000 years ago it was much narrower and sea levels were 70 meters lower. Though the straits were never completely closed, there may have been islands in between which could be reached using simple rafts. Shell middens 125,000 years old have been found in Eritrea,[37] indicating the diet of early humans included seafood obtained by beachcombing.

Extinderea ulterioară

Map of early human migrations[38]

From the Near East, these populations spread east to South Asia by 50,000 years ago, and on to Australia by 40,000 years ago, Homo sapiens for the first time colonizing territory never reached by Homo erectus. Europe was reached by Cro-Magnon some 40,000 years ago. East Asia (Korea, Japan) was reached by 30,000 years ago. It is disputed whether subsequent migration to North America took place around 30,000 years ago, or only considerably later, around 14,000 years ago.

The group that crossed the Red Sea travelled along the coastal route around the coast of Arabia and Persia until reaching India, which appears to be the first major settling point. M is found in high frequencies along the southern coastal regions of Pakistan and India and it has the greatest diversity in India, indicating that it is here where the mutation may have occurred.[39] Sixty percent of the Indian population belong to Haplogroup M. The indigenous people of the Andaman Islands also belong to the M lineage. The Andamanese are thought to be offshoots of some of the earliest inhabitants in Asia because of their long isolation from mainland Asia. They are evidence of the coastal route of early settlers that extends from India along the coasts of Thailand and Indonesia all the way to Papua New Guinea. Since M is found in high frequencies in highlanders from New Guinea as well, and both the Andamanese and New Guineans have dark skin and Afro-textured hair, some scientists believe they are all part of the same wave of migrants who departed across the Red Sea ~60,000 years ago in the Great Coastal Migration. Notably, the findings of Harding et al. (2000, p. 1355) show that, at least with regard to dark skin color, the haplotype background of Papua New Guineans at MC1R (one of a number of genes involved in melanin production) is identical to that of Africans (barring a single silent mutation). Thus, although these groups are distinct from Africans at other loci (due to drift, bottlenecks, etc), it is evident that selection for the dark skin color trait likely continued (at least at MC1R) following the exodus. This would support the hypothesis that suggests that the original migrants from Africa resembled pre-exodus Africans (at least in skin color), and that the present day remnants of this ancient phenotype can be seen among contemporary Africans, Andamanese and New Guineans. Others suggest that their physical resemblance to Africans could be the result of convergent evolution.[40][41]

From Arabia to India the proportion of haplogroup M increases eastwards: in eastern India, M outnumbers N by a ratio of 3:1. However, crossing over into East Asia, Haplogroup N reappears as the dominant lineage. M is predominant in South East Asia but amongst Indigenous Australians N reemerges as the more common lineage. This discontinuous distribution of Haplogroup N from Europe to Australia can be explained by founder effects and population bottlenecks.[42]

Ipoteze alternative

The multiregional hypothesis, initially proposed by Milford Wolpoff, holds that the evolution of humans from H. erectus at the beginning of the Pleistocene 1.8 million years BP to the present day has been within a single, continuous worldwide population. Proponents of multiregional origin reject the assumption of an infertility barrier between ancient Eurasian and African populations of Homo. Multiregional proponents point to the fossil record and genetic evidence in chromosomal DNA. One study suggested that at least 5% of the human modern gene pool can be attributed to ancient admixture, which in Europe would be from the Neanderthals.[43]

A recently discovered fossilized mandible that is putatively a hybrid between Homo sapiens and an earlier hominid, that is likely to be 110,000 years old, has been interpreted as a challenge to the recent out-of-Africa hypothesis. However, some scholars doubt that the fossil represents a Homo sapiens hybrid.[44]

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