Genetic history of Europe

From Wikipedia, the free encyclopedia

This article or section is in need of attention from an expert on the subject. WikiProject Molecular and Cellular Biology or the Molecular and Cellular Biology Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly.

The factual accuracy of this article is disputed. Please see the relevant discussion on the talk page. (July 2007)

Europe Portal

The diversion of Haplogroup F and its descendants.

European populations have a complicated demographic and genetic history, including many layers of successive migrations between different time periods, from the first appearance of Homo sapiens in the Upper Paleolithic to contemporary immigration.

[edit] Relation to other populations

A study by Luigi Luca Cavalli-Sforza of the Stanford University, School of Medicine, using 120 blood polymorphisms provides information on genetic relatedness of the various continental populations^[1]. Genetic distance is a measure used to quantify the genetic differences between two populations. It is based on the principle that two populations that share similar frequencies of a trait are more closely related than populations that have more divergent frequencies of a trait. In its simplest form it is the difference in frequencies of a particular trait between two populations. For example the frequency of RH negative individuals is 50.4% among Basques, 41.2% in France and 41.1% in England. Thus the genetic difference between the Basques and French is 9.2% and the genetic difference between the French and the English is 0.1% for the RH negative trait. Averaged over several traits this can give the overall genetic relatedness of various populations^[2].

According to the study all non-African populations are more closely related to each other than to Africans consistent with the hypothesis that all non-Africans are descended from a single African population. Europeans are most closely related to East Asians and least related to Africans. However of all the non-African populations, Europeans are most closely related to Africans. As the genetic distance from Africa to Europe (16.6) is shorter than the genetic distance from Africa to East Asia (20.6) and even much shorter than the Genetic distance from Africa to Australia. Cavalli-Sforza proposes that the simplest explanation for this short genetic distance is that substantial gene exchange has taken place between the nearby continents. Cavalli-Sforza also proposes that both Asian and African populations contributed to the settlement of Europe which began 40 000 years ago. The overall contributions from Asia and Africa were estimated to be around two-thirds and one-third, respectively. Europe has a genetic variation in general of about a third of that of other continents.^[3][2]

According to Guglielmino et al. (1990),

Principal coordinate analysis shows that Lapps/Sami are almost exactly intermediate between people located geographically near the Ural mountains and speaking Uralic languages, and central and northern Europeans. Hungarians and Finns are definitely closer to Europeans. An analysis of genetic admixture between Uralic and European ancestors shows that Lapps/Sami are slightly more than 50% European, Hungarians are 87% European, and Finns are 90% European. There is basic agreement between these conclusions and historical data on Hungary. Less is known about Finns and very little about Lapps/Sami.^[4]

[edit] European population substructure

European population substructure from 2007 (many of the participants were Americans, not Europeans), a clustering analysis using the computer programme STRUCTURE and 9724 SNPs.

In 2006, an autosomal analysis comparing samples from various European populations concluded that “there is a consistent and reproducible distinction between ‘northern’ and ‘southern’ European population groups”. Most individual participants with southern European ancestry (Italian, Greek, Armenian, Portuguese, and Spanish) have >85% membership in the ‘southern’ population; and most northern, western, eastern, and central Europeans have >90% in the ‘northern’ population group. Ashkenazi Jewish as well as Sephardic Jewish origin also showed >85% membership in the ‘southern’ population, consistent with a later Mediterranean origin of these ethnic groups." [14]It should be noted that many of the participants in this study were actually American citizens who self identified with different European ethnicities and not Europeans.

Somewhat contradicting these findings, a similar 2007 study using samples exclusively from Europe found that the most important genetic differentiation in Europe occurs on a line from the north to the south-east (northern Europe to the Balkans), with another east-west axis of differentiation across Europe. Its findings were consistent with earlier mtDNA and Y-chromosonal based results supporting the theory that modern Iberians (Spanish and Portuguese) hold the most ancient European genetic ancestry, as well as separating Basques and Sami from other European populations. It confirmed that the English and Irish cluster with other Northern and Eastern Europeans such as Germans and Poles while some Basque and Italian individuals also clustered with Northern Europeans. Despite these stratifications it noted the unusually high degree of European homogeneity: "there is low apparent diversity in Europe with the entire continent-wide samples only marginally more dispersed than single population samples elsewhere in the world."^[5]

In fact, according to another European wide study, the main components in the European genomes appear to derive from ancestors whose features were similar to those of modern Basques and Near Easterners, with average values greater than 35% for both these parental populations, regardless of whether or not molecular information is taken into account. The lowest degree of both Basque and Near Eastern admixture is found in Finland, whereas the highest values are, respectively, 70% ("Basque") in Spain and more than 60% ("Near Eastern") in the Balkans.[15][16]

In 2008 a company called "DNA Tribes Europa" has used 13 DNA markers to differentiate genetic related groups in Europe. It offeres a specialized analysis for people of European descent, including a detailed comparison to genetic sub-regions of Europe. These genetic sub-regions include both geographical territories and endogamous trans-national communities, who have retained unique genetic characteristics. The determined regions i.e. populations are the next: Ashkenazi, Balkan, Basque, Celtic, Finno-Ugrian, Germanic, Greek, Italian, Norse, Polish, Portuguese, Russian and Spanish. ^[6] Individuals within each Europe sub-region obtain a spectrum of regional genetic affinities. Because of close genetic relationships within Europe, individuals in a subregion can inherit genetic material that is most common in other sub-regions. Individuals from sub-regions with a history of ethnic endogamy or geographic isolation (such as the Ashkenazi, Basque, or Celtic sub-regions) exhibit higher frequencies of primarily ingroup genetic affiliation. Individuals from centrally located sub-regions, such as the Balkan or Germanic regions, exhibit more variety in genetic affiliations and lower frequencies of primarily in-group genetic affiliation.^[7]

[edit] Haplogroups

[edit] Human Y-chromosome DNA haplogroups

Distribution of R1a (purple) and R1b (red). Two of the three most common Human Y-chromosome DNA haplogroups in Europe. Black represents all the other haplogroups.

There are three major Y-chromosome DNA haplogroups which largely account for most of Europe's present-day population^[8][9].

• Haplogroup R1b is common on the western Atlantic coast of Europe, from the Iberian Peninsula (comprising Spain and Portugal) to Ireland, Wales, England and Scotland, and Jutland.
• Haplogroup I is common across Germany, the Netherlands, Austria, and up into Scandinavia, as well as the western Balkans.
• Haplogroup R1a is common in Eastern Europe (and has also spread across into Central Asia and as far as the Indian subcontinent).

Most common of all haplogroups among western Europeans is R1b.^[10][11] The exact following values of Hg R1b are: Basques: 88.1%; Irish: 81.5%; Welsh: 89.0%; Scots: 77.1%; Non-Basque Spaniards: 68.0 (Catalans: 79.2; Andalusians: 65.5); Portuguese(South): 56.0%; Portuguese (North): 62.0%; British: 68.8; English (Central): 61.9% Belgians: 63.0; French: 52.2; Danes: 41.7%, Norwegian: 25.9; Swedish: 20.0; German: 47.9; Italian (Calabria): 32.4; Italian (Sardinia): 22.1%; Italian (North-central): 62.0. In conclusion, the so-called R1b genetic family is the most numerous in Western Europe.^[12] Each haplogroup also have subclades.^[13] R1a and R1b are subclades of Haplogroup R (Y-DNA)^[14] Two main subgroups of Haplogroup I (Y-DNA) are I-M253/I-M307/I-P30/I-P40 which according to the International Society of Genetic Genealogy, "has highest frequency in Scandinavia, Iceland, and northwest Europe." The other is I-S31 which according to the International Society of Genetic Genealogy, "includes I-P37.2, which is the most common form in the Balkans and Sardinia, and I-S23/I-S30/I-S32/I-S33, which reaches its highest frequency along the northwest coast of continental Europe."^[15]

There is an ongoing debate regarding Neolithic Europe, with evidence both for and against a demic diffusion from the Near East: G Barbujani1 and L Chikhi (2006) state, "Genetic studies have failed to settle the controversy so far, because they have been interpreted in different ways... A rather heated debate followed, and is still continuing."^[16]

Also, around 4,500 years ago, Haplogroup N3 began moving across from west of the Ural mountains, and seems to follow closely the spread of the Finno-Ugric languages.^[8]

[edit] Human mitochondrial DNA haplogroups

About mitochondrial DNA haplogroups (mtDNA), according to University of Oulu Library (Finland):

Classical polymorphic markers (i.e. blood groups, protein electromorphs and HLA antigenes) have suggested that Europe is a genetically homogeneous continent with a few outliers such as the Saami, Sardinians, Icelanders and Basques (Cavalli-Sforza et al. 1993, Piazza 1993). The analysis of mtDNA sequences has also shown a high degree of homogeneity among European populations, and the genetic distances have been found to be much smaller than between populations on other continents, especially Africa (Comas et al. 1997).

The mtDNA haplogroups^[17] of Europeans are surveyed by using a combination of data from RFLP analysis of the coding region and sequencing of the hypervariable segment I. About 99% of European mtDNAs fall into one of ten haplogroups: H, I, J, K, M, T, U, V, W or X (Torroni et al. 1996a). Each of these is defined by certain relatively ancient and stable polymorphic sites located in the coding region (Torroni et al. 1996a)... Haplogroup H, which is defined by the absence of a AluI site at bp 7025, is the most prevalent, comprising half of all Europeans (Torroni et al. 1996a, Richards et al. 1998)... Six of the European haplogroups (H, I, J, K, T and W) are essentially confined to European populations (Torroni et al. 1994, 1996a), and probably originated after the ancestral Caucasoids became genetically separated from the ancestors of the modern Africans and Asians.^[18]

mtDNA Haplogroup N1a while presently rare (0.18%-0.3%) occurred in as many as 25% of Neolithic Europeans and has subsequently been absorbed into the current populations ^[19][20].

[edit] Paleolithic migrations

The prehistory of the European peoples can be traced by the examination of archaeological sites, linguistic studies, and by the examination of the DNA of the people who live in Europe now, or from recovered ancient DNA. Much of this research is ongoing, with discoveries still being continually made, and theories rise and fall.

Europe 20,000 years ago, showing coastline, extent of Ice caps and regions where refugia are thought to have been situated.^[21]

Modern humans (Cro Magnon) began to colonize Europe in the Paleolithic about 40,000 years ago, as evidenced by the spread of the Aurignacian culture. Modern humans may have arrived along two major routes either side of the Black Sea. By about 25,000 years ago the prior inhabitants (our cousin species H. neanderthalensis) were either killed off or absorbed into the population and ultimately became extinct.^[22] About 22,000 years ago the last Ice Age (often referred to as the Last Glacial Maximum or LGM) began, rendering much of Europe uninhabitable. Humans may only have occupied certain regions of Europe at this time, these are often called refuges (or refugia) and were located along the northern Mediterranean and Black Sea coasts, as well as in the Balkans. As the glaciers receded from about 16,000 years ago, the populations that had occupied the refuges are thought to have begun to spread and colonise northern Europe.^[23][24]

After a less severe cold event around 12000-10000 years ago there was an increasing use of microliths and reliance on the coast and sea. Styles of tool making varied from location to location, suggesting that the population of Europe was settling down. Martin Richards showed that about 11% of modern mtDNA types arrived from the Middle East during the Mesolithic ^[25]. These show a significant decline from SE to NW Europe. However Stephen Oppenheimer says that there was further gene flow from Iberia to NW Europe ^[26]. In northern Europe the gene flow was largely from SE Europe and Asia. The population of Europe were hunter-gatherers until the advent of agriculture about eight millennia ago.

[edit] Neolithic migrations

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion.

Further information: Neolithic Europe and Neolithic Revolution

The duration of the Neolithic varied from place to place, starting with the introduction of farming and ending with the introduction of bronze implements. In SE Europe it was approximately 7000-3000 BC while in NW Europe it was 4500-1700 BC. Besides the introduction of new plants and animals, the Neolithic also saw the beginning of the use of pottery. The latter allows the tracing of the movement of ideas and possibly people across Europe. The period possibly also saw the spread of Indo-European languages across Europe. One hypothesis is that they spread with farming while another is they came later from the Pontic steppes by expansion of the Kurgan people.

Some academics ^[27] theorise that farming was introduced by people who migrated from the Near East, and that these farmers introduced the Indo-European languages to Europe. This theory is typically associated with the Anatolian hypothesis of Indo-European origins, though it has also been argued that widespread migration is not necessary to support the theory.^[28]

The largest admixture to the European paleolithic/mesolithic stock was due to the neolithic revolution of the 7th to 5th millennia BC.^[29] Three main mtDNA gene groups have been identified as contributing Neolithic entrants into Europe: J, T1 and U3 (in that order of importance) ^[30]. With others they amount to around 20% of the gene pool ^[31]. There is little published information on male immigration during the Neolithic but Oppenheimer suggests that haplotypes J and Eb3 migrated along the coast of Europe at this time. Gene flow from SE to NW Europe seems to have continued.

[edit] Bronze to Iron Age migrations

The Bronze Age saw the development of long distance trading networks, particularly along the Atlantic Coast and in the Danube valley. There was migration from Norway to Orkney and Shetland in this period (and to a lesser extent to mainland Scotland and Ireland). There was also migration from Germany to eastern England. Oppenheimer could find no genetic evidence for any Iron Age migration to Britain.

Other theories about the origins of the Indo-European language centre around a hypothetical Proto-Indo-European people, who are traced, in the Kurgan hypothesis, to somewhere north of the Black Sea at about 4500 BCE. They domesticated the horse, and are considered to have spread their culture and genes across Europe. It has been difficult to identify what these "Kurgan" genes might be. Another approach – the Anatolian hypothesis – suggests an origin in Anatolia with a later expansion from eastern Europe.

To what extent Indo-European migrations replaced the indigenous Mesolithic peoples is debated, but a consensus has been reached that technology and language transfer played a more important role in this process than actual gene-flow.^[32]

During the Iron Age, Celts are recorded as having moved into northern Italy, Eastern Europe and Anatolia.

[edit] Medieval to Early Modern admixture

Further information: Sub-Saharan DNA admixture in Europe, History of the Roma people, and Turkic expansion

There is some admixture of Sub-Saharan African DNA, due to the Early Modern African slave trade It shows a decreasing cline from the southwest to the northeast, which corresponds with the areas most involved in slave trade. Not every population has been studied yet, but enough have so that a picture is starting to emerge. The amount of black admixture in Europe today ranges from a few percent in Iberia to almost nil around the Baltic.^[33]

According to a summary study by Pereira et al. 2005, sub-Saharan mtDNA L haplogroups were found at rates of 3.83% in Iberians (Portuguese and Spanish), 2.86% in Sardinians, 2.38% in Albanians, 1% in the British/Irish (indigenous whites only), 0.94% in Sicilians, 0.62% in a German-Danish sample.

Sub-Saharan African Y-chromosomes are much less common in Europe, for the reasons discussed above. The small presence of the Haplogroups E(xE3b) (i.e. clades of E other than E3b) and Haplogroup A in Europe is almost exclusively attributable to the slave trade, as these haplogroups are characteristic of western, central and southern Africans and are barely observed elsewhere.^[34] Haplotype A has been detected in Portugal (3%), France (2.5% in a very small sample), Germany (2%), Sardinia (1.6%), Austria (0.78%), Italy (0.45%), Spain (0.42%) and Greece (0.27%). By contrast, North Africans have about 5% paternal sub-Saharan admixture.^[35]

[edit] North and Northeast African influences

There are a number of genetic markers which are characteristic of Horn African and North African populations which are to be found in European populations signifying ancient and modern population movements across the Mediterranean. These markers are to be found particularly in Mediterranean Europe but some are also prevalent, at low levels, throughout the continent. The spread of the Megaliths and its Cultures seem to have been carried, or kept maritime connections with, the Mediterranean and Northern Africans.

[edit] Y-chromosome DNA

The general parent Y-chromosome Haplogroup E1b1b (formerly known as E3b), originating in modern day Somalia, is by far the most common in North and Northeast Africa, and is also common throughout the majority of Europe, particularly in the Mediterranean and South Eastern Europe. E1b1b reaches its highest concentration in Greece and the Balkan region, but also enjoys a significant presence in other regions such as Hungary, Italy, Iberia and Austria. [17].^[36].

Outside of the Horn of Africa, E1b1b's two most prevalent clades are E1b1b1a (E-M78, formerly E3b1a) and E1b1b1b (E-M81, formerly E3b1b).

E1b1b1a is the most common subclade of E1b1b and is present throughout Europe. Its main route of entry into the European continent was through Anatolia during the Neolithic, explaining the high frequency of this haplotype in the Balkan region. It is also relatively frequent in the Mediterranean countries. Unlike, E1b1b1b which is thought to have entered Europe in more recent times, this haplotype denotes a very ancient Northeast African contribution to the European gene-pool.

A study from Semino (published 2004) showed that Y-chromosome haplotype E1b1b1b (E-M81), is specific to North African populations and almost absent in Europe except the Iberia (Spain and Portugal) and Sicily.^[37] Another 2004 study showed that E1b1b1b is found present, albeit at low levels throughout Southern Europe (ranging from 1.5% in Northern Italians, 2.2% in Central Italians, 1.6% in southern Spaniards, 3.5% in the French, 4% in the Northern Portuguese, 12.2% in the southern Portuguese and 41.2% in the genetic isolate of the Pasiegos from Cantabria)^[38]. The findings of this latter study contradict a more thorough analysis Y-chromosome analysis of the Iberian peninsula according to which haplogroup E1b1b1b surpasses frequencies of 10% in Southern Spain. The study points only to a very limited influence from northern Africa and the Middle East both in historic and prehistoric times.^[39] The absence of microsatellite variation suggests a very recent arrival from North Africa consistent with historical exchanges across the Mediterranean during the period of Islamic expansion, namely of Berber populations.^[36]. However a more thorough study about Y-chromosome lineages in Portugal revealed that "The mtDNA and Y data indicate that the Berber presence in that region dates prior to the Moorish expansion in 711 AD... Our data indicate that male Berbers, unlike sub-Saharan immigrants, constituted a long-lasting and continuous community in the country".^[40]

Haplotype V(p49/TaqI), a characteristic North African haplotype, may be also found in the Iberian peninsula, and a decreasing North-South cline of frequency clearly establishes a gene flow from North Africa towards Iberia which is also consistent with Moorish presence in the peninsula.[18]. This North-South cline of frequency of halpotype V is to be observed throughout the Mediterranean region, ranging from frequencies of close to 50% in southern Portugal to around 10% in southern France. Similarly, the highest frequency in Italy is to be found in the southern island of Sicily (28%).[19] ^[41]

A wide ranging study (published 2007) using 6,501 unrelated Y-chromosome samples from 81 populations found that: “Considering both these E-M78 sub-haplogroups (E-V12, E-V22, E-V65) and the E-M81 haplogroup, the contribution of northern African lineages to the entire male gene pool of Iberia (barring Pasiegos), continental Italy and Sicily can be estimated as 5.6%, 3.6%, and 6.6%, respectively.”^[42]

[edit] Mitochondrial DNA

Genetic studies on Iberian populations also show that North African mitochondrial DNA sequences (haplogroup U6) and sub-Saharan sequences (Haplogroup L), although present at only low levels, are still at much higher levels than those generally observed elsewhere in Europe. ^[43][44][45] Haplotype U6 have also been detected in Sicily at very low levels. It happens also to be a characteristic genetic marker of the Saami populations of Northern Scandinavia.[20] It is difficult to ascertain that U6's presence is the consequence of Islam's expansion into Europe during the Middle Ages, particularly because it is more frequent in the north of the Iberian Peninsula rather than in the south. In smaller numbers it is also attested too in the British Islands, again in its northern and western borders. It may be a trace of a prehistoric neolithic/megalithic expansion along the Atlantic coasts from North Africa, perhaps in conjunction with seaborne trade. One subclade of U6 is particularly common among Canarian Spaniards as a result of native Guanche (proto-berber) ancestry.

On the other hand, the distribution of mtDNA Haplogroup L, is consistent with modern historical data, being more frequent in Iberia than in the rest of Europe and more frequent in the south of the peninsula than in the north. Islamic domination, as well as the slave trade, is likely to have been a factor leading to its presence in some modern-day southern Iberian populations.

[edit] Footnotes

[edit] See also

• Caucasoid
• European ethnic groups
• Human genetic variation
• Population genetics
• Archaeogenetics of the Near East
• White people

[edit] External links

• Atlas of the Human Journey
• World Haplogroups Maps
• Origins of Europeans
• Genetic Structure of Human Populations.
• Haplotype R1b
• Haplogroup R1b
• Haplogroup R1b