The genetic history of Europe can be inferred from the patterns of genetic diversity across continents and time. The primary data to develop historical scenarios coming from sequences of mitochondrial, Y-chromosome and autosomal DNA from modern populations and if available from ancient DNA. European populations have a complicated demographic and genetic history, including many successive periods of population growth.

The diversion of Y chromosome haplogroup Haplogroup F and its descendants.

Genetic studies[link]

One of the first scholars to perform genetic studies was Luigi Luca Cavalli-Sforza. He used classical genetic markers to analyse DNA by proxy. This method studies differences in the frequencies of particular allelic traits, namely polymorphisms from proteins found within human blood (such as the ABO blood groups, Rhesus blood antigens, HLA loci, immunoglobulins, G-6-P-D isoenzymes, amongst others). Subsequently his team calculated genetic distance between populations, 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 the trait. From this, he constructed phylogenetic trees which showed genetic distances diagrammatically. His team also performed principal component analyses, which is good at analysing multivariate data with minimal loss of information. The information that is lost can be partly restored by generating a second principal component, and so on.^[1] In turn, the information from each individual principal component (PC) can be presented graphically in synthetic maps. These maps show peaks and troughs, which represent populations whose gene frequencies take extreme values compared to others in the studied area.^[2]

Peaks and troughs usually, but not necessarily, connected by smooth gradients, called clines. Genetic clines can be generated in several ways: including adaptation to environment (natural selection), continuous gene flow between two initially different populations, or a demographic expansion into a scarcely populated environment with little initial admixture with pre-existing populations.^[3] Cavalli-Sforza connected these gradients with postulated pre-historic population movements based on known archaeological and linguistic theories. However, given that the time depths of such patterns are not known, "associating them with particular demographic events is usually speculative".^[4]

Studies using direct DNA analysis are now abundant, and may utilize mitochondrial DNA (mtDNA), the non-recombining portion of the Y chromosome (NRY) or autosomal DNA. MtDNA and NRY DNA share some similar features which have made them particularly useful in genetic anthropology. These properties include the direct, unaltered inheritance of mtDNA and NRY DNA from mother to offspring, and father to son, respectively, without the 'scrambling' effects of genetic recombination. We also presume that these genetic loci are not affected by natural selection, and that the major process responsible for changes in base pairs has been mutation (which can be calculated).^[5]

The smaller effective population size of the NRY and mtDNA enhances the consequences of drift and founder effect relative to the autosomes, making NRY and mtDNA variation a potentially sensitive index of population composition.^[4][6][7] However, these biologically plausible assumptions are nevertheless not concrete. For example, Rosser suggests that climatic conditions may affect the fertility of certain lineages.^[4]

Even more problematic, however, is the underlying mutation rate used by the geneticists. They often use different mutation rates, and therefore studies frequently arrive at vastly different conclusions.^[4] Moroever, NRY and mtDNA may be so susceptible to drift that some ancient patterns may have become obscured over time. Another implicit assumption is that population genealogies are approximated by allele genealogies. Barbujani points out that this only holds if population groups develop from a genetically monomorphic set of founders. However, Barbujani argues that there is no reason to believe that Europe was colonized by monomorphic populations. This would result in an overestimation of haplogroup age, thus falsely extending the demographic history of Europe into the Late Paleolithic rather than the Neolithic era.^[8] (See also Genetic drift, Founder effect, Population bottleneck.) Greater certainty about chronology may be obtained from studies of ancient DNA (see below), but so far these have been comparatively few.

Whereas Y-DNA and mtDNA haplogroups represent but a small component of a person’s DNA pool, autosomal DNA has the advantage of containing hundreds and thousands of examinable genetic loci, thus giving a more complete picture of genetic composition. However, descent relationships can only to be determined on a statistical basis because autosomal DNA undergoes recombination. A single chromosome can record multiple histories; a separate history for each gene. Autosomal studies are much more reliable for showing the relationships between existing populations but do not offer the possibilities for unraveling their histories in the same way as mtDNA and NRY DNA studies promise, despite their many complications.

Genetic studies operate on numerous assumptions and suffer from usual methodological limitations such as selection bias and confounding. Phenomenon like genetic drift, foundation and bottleneck effects cause large errors, particularly in haplogroup studies. Furthermore, no matter how accurate the methodology, conclusions derived from such studies are ultimately compiled on the basis of how the author envisages their data fits with established archaeological or linguistic theories.

Relation between Europeans and other populations[link]

According to Cavalli-Sforza's work, all non-African populations are more closely related to each other than to Africans; supporting the hypothesis that all non-Africans descend from a single old-African population. The genetic distance from Africa to Europe (16.6) was found to be shorter than the genetic distance from Africa to East Asia (20.6), and much shorter than that from Africa to Australia (24.7). He explains:

...both Africans and Asians contributed to the settlement of Europe, which began about 40,000 years ago. It seems very reasonable to assume that both continents nearest to Europe contributed to its settlement, even if perhaps at different times and maybe repeatedly. It is reassuring that the analysis of other markers also consistently gives the same results in this case. Moreover, a specific evolutionary model tested, i.e., that Europe is formed by contributions from Asia and Africa, fits the distance matrix perfectly (6). In this simplified model, the migrations postulated to have populated Europe are estimated to have occurred at an early date (30,000 years ago), but it is impossible to distinguish, on the basis of these data, this model from that of several migrations at different times. The overall contributions from Asia and Africa were estimated to be around two-thirds and one-third, respectively".

—^[9][10][11]

This particular model used an Out of Africa migration 100,000 years ago which separated Africans from non-Africans followed by a single admixture event 30,000 years ago leading to the formulation of the European population. The admixture event consisted of a source population that was 35% African and 65% East Asian. However the study notes that a more realistic scenario would include several admixture events occurring over a sustained period. In particular they cite the spread of farming from a source population in West Asia 5000–9000 years ago may have played a role in the genetic relatedness of Africans and Europeans since West Asia is sandwiched in between Africa and Central Asia. The model assumed an out of Africa migration 100kya and a single admixture event 30kya. However, most contemporary studies have more recent dates that place the out of Africa migration 50-70kya. The study also involved a direct comparison between Sub-Saharan Africans (Central Africans and Senegalese) and Europeans. North Africans population were omitted from the study as they are known to have both Eurasian and Sub-Saharan admixture. These considerations might help explain the apparent short genetic distance between Europeans and Africans^[9][10][11]

A later study by Bauchet, which utilised ~ 10 thousand autosomal DNA SNPs arrived at similar results. Principal component analysis clearly identified four widely dispersed groupings corresponding to Africa, Europe, Central Asia and South Asia. PC1 separated Africans from the other populations, PC2 divided Asians from Europeans and Africans, whilst PC3 split Central Asians apart from South Asians.^[12]

European population sub-structure[link]

Cavalli-Sforza's 1st Principal Component:A cline of genes with highest frequencies in the Near East, spreading to lowest levels northwest

Geneticists agree that Europe is the most genetically homogeneous of all the continents.^[13][14] However, some patterns are discernible. Cavalli-Sforza’s principal component analyses revealed five major clinal patterns throughout Europe, and similar patterns have continued to be found in more recent studies.^[15]

1. A cline of genes with highest frequencies in the Middle East, spreading to lowest levels northwest. Cavalli-Sforza originally described this as faithfully reflecting the spread of agriculture in Neolithic times. This has been the general tendency in interpretation of all genes with this pattern.
2. A cline of genes with highest frequencies amongst Finnish and Saami in the extreme north east, and spreading to lowest frequencies in the south west.
3. A cline of genes with highest frequencies in the area of the lower Don and Volga rivers in southern Russia, and spreading to lowest frequencies in Iberia, Southern Italy, Greece and the areas inhabited by Saami speakers in the extreme north of Scandinavia. Cavalli-Sforza associated this with the spread of Indo-European languages, which he links in turn to a "secondary expansion" after the spread of agriculture, associated with animal grazing.
4. A cline of genes with highest frequencies in the Balkans and Southern Italy, spreading to lowest levels in Britain and the Basque country. Cavalli-Sforza associates this with "the Greek expansion, which reached its peak in historical times around 1000 and 500 BC but which certainly began earlier"
5. A cline of genes with highest frequencies in the Basque country, and lower levels beyond the area of Iberia and Southern France. In perhaps the most well-known conclusion from Cavalli-Sforza this weakest of the 5 patterns was described as isolated remnants of the pre-Neolithic population of Europe, "who at least partially withstood the expansion of the cultivators". It corresponds roughly to the geographical spread of rhesus negative blood types. In particular, the conclusion that the Basques are a genetic isolate has become widely discussed, but also a controversial conclusion.

He also created a phylogenetic tree to analyse the internal relationships amongst Europeans. He found four major 'outliers'- Basques, Lapps, Finns and Icelanders; a result he attributed to their relative isolation (note: with the exception of the Icelanders, the rest of the groups speak non-Indo-European languages). Greeks and Yugoslavs represented a second group of less extreme outliers. The remaining populations clustered into several groups : "Celtic", "Germanic", "south-western Europeans", "Scandinavians" and "eastern Europeans".^[16]

Genetic studies after Cavalli-Sforza[link]

Parts of this article (those related to section) are outdated. Please update this article to reflect recent events or newly available information. Please see the talk page for more information. (November 2009)

Human Y-chromosome DNA haplogroups[link]

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 big Y-chromosome DNA haplogroups which account for most of Europe's patrilineal descent.^[17]

• Haplogroup R1b is common all over Europe but especially common in Western Europe.^[18][19][20] Nearly all of this R1b in Europe is in the form of the R1b1a2 (2011 name) (R-M269) sub-clade, specifically within the R-L23 sub-sub-clade whereas R1b found in Central Asia, western Asia and Africa tends to be in other clades. It has also been pointed out that outlier types are present in Europe and are particularly notable in some areas such as Sardinia.^[21] Haplogroup R1b frequencies vary from highs in western Europe in a steadily decreasing cline with growing distance from the Atlantic: 80-90% (Welsh, Basques, Irish, Scots, north-western Spanish, Portuguese and western French); around 40-60% in most other parts of western Europe. It drops outside this area and is around 20% or less in areas such as southern Italy, Sweden, Poland, the Balkans and Cyprus. R1b remains the most common clade as one moves east to Germany, while further east in Poland, R1a is more common (see below).^[22] In southeastern Europe, R1b drops behind R1a in the area in and around Hungary and Serbia but is more common both to the south and north of this region.^[23] R1b in Western Europe is dominated by at least two sub-clades, R-U106, which is distributed from the east side of the Rhine into northern and central Europe (with a presence in England) and R-P312, which is most common west of the Rhine, including the British Isles.^[19][20]

• Haplogroup I is found in the form of various sub-clades throughout Europe and is found at highest frequencies in Bosnia and Herzegovina, Croatia, Sweden, Norway, Sardinia, parts of Germany and other countries in the Balkan Peninsula and Scandinavia. This clade is found at its highest expression by far in Europe and may have been there since before the LGM.^[24]
• Haplogroup R1a, almost entirely in the R1a1a sub-clade, is prevalent in much of Eastern and Central Europe (also in South and Central Asia). For example there is a sharp increase in R1a1 and decrease in R1b1b2 as one goes east from Germany to Poland.^[22] It also has a substantial presence in Scandinavia (particularly Norway),^[25][26] and some small pockets in Southern Europe, for example the Pas Valley^[27] areas of Venice, and Calabria in Italy.^[28] In the Baltic countries R1a frequencies decrease from Lithuania (45%) to Estonia (around 30%).^[29]

Putting aside small enclaves there are also several haplogroups apart from the above three, which are most common in certain areas of Europe.

• Haplogroup N is common only in the northeast of Europe and in the form of its N1c1 sub-clade reaches frequencies of approximately 60% among Finns and approximately 40% among Lithuanians. This clade is also found far into the east in Siberia, Japan and China.

• Haplogroup E1b1b1, mainly in the form of its E1b1b1a2 (E-V13) sub-clade reaches frequencies above 40% around the area of Kosovo.^[30] This clade is thought to have arrived in Europe from western Asia either in the later Mesolithic,^[31] or the Neolithic.^[32]

• Haplogroup J, in various sub-clades is found in levels of around 15-30% in parts of the Balkans and Italy.^[33]

X chromosome[link]

In recent times it has been proposed that X chromosome haplotypes are particularly useful for locating some of the oldest surviving lineages in humanity.^[34]

Human mitochondrial DNA haplogroups[link]

There have been a number of studies about the mitochondrial DNA haplogroups (mtDNA) in Europe. In contrast to Y DNA haplogroups, mtDNA haplogroups did not show as much geographical patterning, but were more evenly ubiquitous. Apart from the outlying Saami, all Europeans are characterized by the predominance of haplogroups H, U and T. The lack of observable geographic structuring of mtDNA may be due to socio-cultural factors, namely the phenomena of polygyny and patrilocality.^[4] According to the University of Oulu Library in 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^[35] 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.^[36]

Genetic studies suggest some maternal gene flow to eastern Europe from eastern Asia or southern Siberia 13,000 - 6,600 years BP.^[37] Analysis of Neolithic skeletons in the Great Hungarian Plain found a high frequency of eastern Asian mtDNA haplogroups, some of which survive in modern eastern European populations.^[37] Maternal gene flow to Europe from sub-Saharan Africa began as early as 11,000 years BP, although the majority of lineages, approximately 65%, are estimated to have arrived more recently, including during the Romanization period, the Arab conquests of southern Europe, and during the Atlantic slave trade.^[38]

Ancient DNA[link]

The genetic history of Europe has mostly been reconstructed from the modern populations of Europe, assuming genetic continuity^[when?]. This is because it is far easier to retrieve DNA from living subjects than ancient human remains. However, a small number of ancient mtDNA and Y-DNA analyses are available from both the historical and prehistoric periods.

Autosomal DNA[link]

Seldin (2006) used over five thousand autosomal SNPs. It showed "a consistent and reproducible distinction between ‘northern’ and ‘southern’ European population groups". Most individual participants with southern European ancestry (Italians, Greeks, Portuguese, Spaniards), and Ashkenazi Jews have>85% membership in the ‘southern’ population; and most northern, western, central, and eastern Europeans (Swedes, English, Irish, Germans, and Ukrainians) have>90% in the ‘northern’ population group. However, many of the participants in this study were actually American citizens who self-identified with different European ethnicities based on self-reported familial pedigree.^[39]

A similar study in 2007 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 results based on mtDNA and Y-chromosonal DNA that support 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 suggested 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."^[40]

In 2008, two international research teams published analyses of large-scale genotyping of large samples of Europeans, using over 300,000 autosomal SNPs. With the exception of usual isolates such as Basques, Finns and Sardinians, the European population lacked sharp discontinuities (clustering) as previous studies have found (see Seldin et al. 2006 and Bauchett et al. 2007), although there was a discernible south to north gradient. Overall, they found only a low level of genetic differentiation between subpopulations, and differences which did exist were characterized by a strong continent-wide correlation between geographic and genetic distance. In addition, they found that diversity was greatest in southern Europe due a larger effective population size and/or population expansion from southern to northern Europe.^[41] The researchers take this observation to imply that genetically, Europeans are not distributed into discrete populations.^[42][43]

A study in May 2009 ^[44] of 19 populations from Europe using 270,000 SNPs highlighted the genetic diversity or European populations corresponding to the northwest to southeast gradient and distinguished "four several distinct regions" within Europe:

• Finland, showing the greatest distance to the rest of Europeans.
• the Baltic region (Estonia, Latvia and Lithuania), western Russia and eastern Poland.
• Central and Western Europe.
• Italy, "with the southern Italians being more distant".

In this study, barrier analysis revealed "genetic barriers" between Finland, Italy and other countries and interestingly, barriers could also be demonstrated within Finland (between Helsinki and Kuusamo) and Italy (between northern and southern part, Fst=0.0050). Fst (Fixation index) was found to correlate considerably with geographic distances ranging from ≤0.0010 for neighbouring populations to 0.0200-0.0230 for Southern Italy and Finland. For comparisons, pair-wise Fst of non-European samples were as follows: Europeans – Africans (Yoruba) 0.1530; Europeans – Chinese 0.1100; Africans (Yoruba) – Chinese 0.1900.^[45]

A study by Chao Tian in August 2009 extended the analysis of European population genetic structure to include additional southern European groups and Arab populations (Palestinians, Druzes...) from the Near-East. This study determined autosomal Fst between 18 population groups and concluded that, in general, genetic distances corresponded to geographical relationships with smaller values between population groups with origins in neighboring countries/regions (for example, Greeks/Tuscans: Fst=0.0010, Greeks/Palestinians: Fst=0.0057) compared with those from very different regions in Europe (for example Greeks/Swedish: Fst=0.0087, Greeks/Russians: Fst=0.0108).^[46][47]

Autosomal genetic distances (Fst) based on SNPs (2009)[link]

The genetic distance between populations is often measured by Fixation index (Fst), based on genetic polymorphism data, such as single-nucleotide polymorphisms (SNPs) or microsatellites. Fst is a special case of F-statistics, the concept developed in the 1920s by Sewall Wright. Fst is simply the correlation of randomly chosen alleles within the same sub-population relative to that found in the entire population. It is often expressed as the proportion of genetic diversity due to allele frequency differences among populations. The values range from 0 to 1. A zero value implies that the two populations are panmixis, that they are interbreeding freely. A value of one would imply that the two populations are completely separate. The greater the Fst value, the greater the genetic distance. Essentially, these low Fst values suggest that the majority of genetic variation is at the level of individuals within the same population group (~ 85%); whilst belonging to a different population group within same ‘race’/ continent, and even to different racial/ continental groups added a much smaller degree of variation (3-8%; 6-11%, respectively).

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CEU - Utah residents with ancestry from Northern and Western Europe.