N1a lineages found among Central European early Neolithic people (Western The Origin of the N1a lineages – of West Asian origin, or from Eastern, Southern or local Central Europe?
- Oct 30, 2013
- 7 min read
The ancestry of modern Europeans is a subject of debate among geneticists, archaeologists, and anthropologists. A crucial question is the extent to which Europeans are descended from the first European farmers in the Neolithic Age 7500 years ago or from Paleolithic hunter-gatherers who were present in Europe since 40,000 years ago.
The mysterious N1a mtDNA type is currently rare anywhere in the world. It is carried by only 0.2 percent of Europeans. But it has a high frequency among these Neolithic Europeans – 25 percent of the samples, which means the true population frequency was likely between 8 and 42 percent. Maybe “selection” is the key.
Haplogroup N1a (mtDNA) originated in the Near East 12,000 to 32,000 years ago. Specifically, the Arabian Peninsula is postulated as the geographic origin of N1a. This supposition is based on the relatively high frequency and genetic diversity of N1a in modern populations of the peninsula. Exact origins and migration patterns of this haplogroup are still subject of some debate.
Relatively high frequencies of N1a are found in the modern population of Saudi Arabia. Estimates range from 2.4% to 4%. Regional analysis revealed that the haplogroup was most common in the center of the country. Haplotype diversity is noted for being higher here than elsewhere.
Frequencies of N1a in Yemen are relatively high, with estimates varying by study: 3.6%, 5.2%, and 6.9%. Yemen is noted for high haplotype diversity within the population. Elsewhere in the Near East, prevalence of N1a is lower. A 2008 article cited population frequencies of 1.1% in Qatar, 0.3% in Iran, and 0.2% in Turkey.
It is estimated that N1a coalesced some 19,600 to 23,500 years ago in West Asia. Its subclades N1a1 and N1a1a1 may have formed between 6,800 and 10,700 years ago, already in Europe, while N1a1a2 may have coalesced in a later date: 3,400-4,000 years ago, making it a good candidate for a Neolithic-specific expansion.
Two main competing scenarios exist for the spread of the Neolithic from the Near East to Europe: Demic diffusion (in which farming is brought by farmers) vs. Cultural diffusion (in which farming is spread by the passage of ideas).
Here we have a common variant in Europe only 7500 years ago that today is almost gone. You might therefore expect that some clever geneticists would claim that the Neolithic farmers contributed little or no genetic ancestry to living Europeans.
An analysis of ancient DNA from early European farmers extracted and sequenced intact stretches of maternally inherited mitochondrial DNA (mtDNA) from 24 out of 57 Neolithic skeletons from various locations in Germany, Austria, and Hungary found that 25% of the Neolithic farmers had one characteristic mtDNA type and that this type formerly was widespread among Neolithic farmers in Central Europe.
Europeans today have a 150-times lower frequency (0.2%) of this mtDNA type, revealing that these first Neolithic farmers did not have a strong genetic influence on modern European female lineages. These finding lends weight to a proposed Paleolithic ancestry for modern Europeans.
These simulations reject the simple hypothesis in which modern Europeans are direct descendants of these first farmers and have lost N1a mainly by genetic drift. Hence the simulations confirm that the first farmers in Central Europe had limited success in leaving a genetic mark on the female lineages of modern Europeans. This is in contrast to the success of the Neolithic farming culture itself, which subsequently spread all over Europe, as the archaeological record demonstrates.
One possible explanation is that the farming culture itself spread without the people originally carrying these ideas. This includes the possibility that small pioneer groups carried farming into new areas of Europe, and that once the technique had taken root, the surrounding hunter-gatherers adopted the new culture and then outnumbered the original farmers, diluting their N1a frequency to the low modern value.
Archaeological research along the Western periphery of LBK and isotope studies of some of our sampled individuals seem to support the idea that male and female hunter-gatherers were integrated into the Neolithic communities. This hypothesis implies that N1a was rare or absent in Mesolithic Europeans, which may be a reasonable assumption given the rarity of the N1a type anywhere in the world (Fig. 3). An alternative hypothesis is a subsequent post early-Neolithic population replacement in Europe, eliminating most of the N1a types. Archaeological evidence for such an event is as yet scant.
This idea depends on several unknowns. It proposes that European hunter-gatherers who were contemporary with the LBK culture had very different mtDNA types – indeed, that they had the types that are presently common. And it proposes that the intrinsic growth rate of agriculturalists was very small, so that their genes were flooded by hunter-gatherers transitioning to agriculture.
But if their genes were so flooded at every stage of their expansion, then the N1a mtDNA sequences shouldn’t be there — they should have been left behind in the Near East. So this is a very curious event – an expanding population saw one of its major mtDNA variants greatly contract in frequency, so much so that today it is nearly gone.
Tracing the genetic origin of central European farmer N1a lineages can provide a unique opportunity to assess the patterns of the farming technology spread into central Europe in the human prehistory. The geographic origin and expansion of farmer lineages related N1a subclades have been deduced. The phylogeographic analysis revealed that the central European farmer lineages have originated from different sources: from eastern Europe, local central Europe, and from the Near East via southern Europe.
The results obtained emphasize that the arrival of central European farmer lineages did not occur via a single demic diffusion event from the Near East at the onset of the Neolithic spread of agriculture into Europe. Indeed these results indicate that the Neolithic transition process was more complex in central Europe and possibly the farmer N1a lineages were a result of a ‘leapfrog’ colonization process.
During the past thirty years, Cavalli-Sforza and others have pushed a model called “demic diffusion” for Neolithic Europe – essentially the idea that population growth resulted in the net movement of Near Eastern genes across Europe. But there are other models for population interactions as agriculture spread and populations became more dense – including long-distance colonizations, elite dominance by one group or another, cultural diffusion without significant genetic movement, and so on.
The evidence from phylogeographic analysis of N1a lineages emphasizes that European farmer N1a lineages might have been originated from different sources- from eastern Europe (for N1a1a1), from Near East via southern Europe (for N1a1b and perhaps for N1a1a3), and from local central European source (for N1a1a2). It is thus clear that Neolithic farmers’ migration into central Europe did not occur in a uniform way; indeed these results indicate that the Neolithic transition process was more complex in central Europe and possibly the farmer N1a lineages were brought in through the ‘leapfrog’ colonization process.
The main question recently has been about the strength of net movement of genes into Europe. Some have claimed that the majority of present European genes can be traced to the Near East before 6000 years ago. Others have argued that the genetic influence of West Asian populations was substantially more minor, or at least had extended over a longer time from the Upper Paleolithic to the present, instead of being concentrated in the Neolithic revolution itself.
The widespread distribution of the N1a lineage in Early and Middle Neolithic northwestern Europe may indicate genetic continuity from Mesolithic populations. This scenario would support a Mesolithic contribution to the earliest Neolithic of Atlantic Europe. This would imply that the N1a lineage was already common in indigenous north European populations and that the spread of the Neolithic was principally the result of cultural diffusion.
Although so far the N1a lineage has not been encountered among late European hunter-gatherers in central and north Europe (Bramanti et al., 2009; Malmstro¨m et al., 2009), it is worth noting that less than half of the hunter-gatherers’ paleogenetic data come indeed from the pre-Neolithic period (predating LBK expansion).
Finally, no paleogenetic data currently exist for the Mesolithic period in Western Europe. This prevents any conclusion being drawn about N1a occurrence during the Mesolithic period in those regions.
Of course we won’t know if N1a occurred in France prior to the Neolithic until we test pre-Neolithic French samples. However, if N1a was present in France prior to the Neolithic, then why wasn’t it present in central-northern Europe where substantial sample sizes exist?
This would require a partition of pre-Neolithic populations of Europe, and also existence of N1a in both the Linearbandkeramik (that spread on a south-north vector) and in Mesolithic French. So, while we wait for pre-Neolithic Western Europeans to come up N1a, I’m willing to wager that they will not, and that N1a spread into France with the Neolithic or the later spread of Megalithic cultures.
Recent paleogenetic studies have confirmed that the spread of the Neolithic across Europe was neither genetically nor geographically uniform. To extend existing knowledge of the mitochondrial European Neolithic gene pool, we examined six samples of human skeletal material from a French megalithic long mound (c.4200 cal BC). We retrieved HVR-I sequences from three individuals and demonstrated that in the Neolithic period the mtDNA haplogroup N1a, previously only known in central Europe, was as widely distributed as western France.
Alternative scenarios are discussed in seeking to explain this result, including Mesolithic ancestry, Neolithic demic diffusion, and long-distance matrimonial exchanges.
In light of the limited Neolithic ancient DNA (aDNA) data currently available, we observe that all three scenarios appear equally consistent with paleogenetic and archaeological data. In consequence, we advocate caution in interpreting aDNA in the context of the Neolithic transition in Europe. Nevertheless, our results strengthen conclusions demonstrating genetic discontinuity between modern and ancient Europeans whether through migration, demographic or selection processes, or social practices.
In 2010, researchers led by Palanichamy conducted a genetic and phylogeographic analysis of N1a. Based on the results, they conclude that some of the LBK samples were indigenous to Europe while others may have resulted from ‘leapfrog’ colonization. Deguilloux’s team agreed with Haak’s conclusion on a genetic discontinuity between ancient and modern Europeans. However, they consider demic diffusion, cultural diffusion, and long-distance matrimonial exchanges all equally plausible explanations for the current genetic findings.
Comments