10-28-2004, 12:46 AM
GENETIC CONTINUITY AND THE LAST GLACIATION
Can the genetic record tell us more about the ebb and flow of populations in the real human sense of where they came from and went to, rather than the inferred cultural picture of what they were doing, as the cold grip of the ice took hold? Genetic tracing can and does fit the archaeological record of that time rather nicely, but it also tells us something much more relevant and general to European roots: that 80 per cent of modern European lines are essentially derived from ancestors who were present in Europe before the Big Freeze.
An important European maternal clan 'HV' spread from Eastern into Northern and Western Europe, perhaps heralding the beginning of the Early Upper Palaeolithic 33,000 years ago. The HV clan is now widespread and fairly evenly distributed in Europe. H is the single, commonest line of all. It was not always so, and a specific sister cluster of the H clan, V, who were probably born in the Basque country, tells us why. The archaeology shows us how the south-western refuge of the Basque country drew cultures and presumably people down from north-west Europe during the lead-up to the Ice Age. Since Western Europe is separated from Italy by mountains, we would expect the reverse process after the Ice age as people re-expanded again from the Basque country and north along the Atlantic coast. This is exactly the picture left by the post-glacial spread of the maternal subgroup V, which has its highest frequency, diversity, and age in the Basque country, falling off as one goes north and only present in rather low frequencies in Italy. V arose in the Basque country shortly after the LGM. Her pre-V ancestor has been dated to 26,400 years ago, long before the LGM. Pre-V is still found farther east in the Balkans and Trans-Caucasus, consistent with her ultimate eastern origin. Even the post-glacial dates of expansion of V (16,300 years in the west) fit this scenario. Exactly the same pattern was seen for the Y-chromosome marker Ruslan, who we saw had moved into northern Europe from the east and found his home in Northern and Western Europe. The present-day picture shows Ruslan at his maximum frequency of 90 per cent in the Spanish Basque country, with the next-highest rates in Western and Northern Europe.
Italy, on the other hand, capped as it is by the Alps, was less a refuge for northern populations than a temperate region of continuous occupation by Mediterranean folk present from before the LGM. This is reflected again in the high proportion (over one-third of the total) of persisting preglacial mtDNA lines found in that region. We can see from these examples that the refuge zones are characterized by dramatic expansions of lines born locally in the refuge zones during the LGM, and also by high rates of persisting lines left over from the preglacial period. The latter pattern is certainly a feature of the Ukraine refuge, which as predicted by the archaeology retains 31 per cent of its preglacial maternal lines. A slightly less convincing case can be made for south-eastern Europeand the Balkans, which retained 24â26 per cent of preglacial lines.
It should be clarified that just because 20â34 per cent of modern European mtDNA lines have been retained from before the LGM, that does not mean that the rest of the lines found today had to have entered Europe from outside after the LGM. No, they were mostly locals. Of all modern European lines, 55 per cent originated in the period just after the ice age (the Late Upper Palaeolithic) but these, like the V haplogroup, probably derived from pre-existing European lines and simply reflect the post-glacial re-expansions from the refuges â in other words, new shoots off an old stock. Real fresh immigration into Europe from the Near East during the Neolithic period (from 8,000 years ago onwards) perhaps accounts for only 15 per cent of modern lines.
An interesting recent discovery about the genetic make-up of the south-eastern European region has to do with Y chromosome markers in Romania. The Carpathian Mountains were glaciated during the Ice Age and thus formed an effective, jagged barrier between south-eastern Europe and the regions bordering the Black Sea. This barrier splits Romania in two from top to bottom. Without their ice, the Carpathians hardly constitute an insurmountable physical barrier today, but they still mark a clear genetic boundary. This is revealed by Y-chromosome markers characteristic of north-eastern Europe and the Ukraine occurring at higher rates to the east of the Carpathians, while the markers more characteristic of Central Europe are found to the west. But this micro-regional boundary is very much obscured by the great dominance of the main Eastern European Y lineage M17, which may characterize the original preglacial Eastern Gravettian intrusions from the east. This lineage is found at very high rates throughout Eastern Europe â from Poland, through Slovakia and Hungary, to the Ukraine. M17 is still found at high frequencies among the Slavic peoples of the Balkans, which could support the existence of the Balkan ice-age refuge.
Again, in Northern Asia, the genetic record tells us that these hardy hunters of the permafrost retained some of their ancient maternal lines from before the LGM, and that there were subsequent expansions of certain subgroups after the thaw. MtDNA lines A, C, and Z are characteristic of North Asia, while D also extends farther south in China. Of these lines, A clearly survived from well before the LGM, as did various M and N lines. Then there was a gap of 10,000 years until about 17,000 years ago, before the re-expansion of lines such as variants of D, A, C, and finally Z.
<b>The genetics of North and Central Asia has simply confirmed what we might expect from the archaeology: when it got cold, the hunters of the Mammoth Steppe shrank in range and hunkered down, and when it got warm again they bounced back and reexpanded. The more interesting questions are what they looked like, and who their closest local descendants are today. Why and when did Mongoloids become the dominant types throughout most of Asia and the Americas? Does the genetic story tell us anything that cannot be inferred from the archaeological record?</b>
Can the genetic record tell us more about the ebb and flow of populations in the real human sense of where they came from and went to, rather than the inferred cultural picture of what they were doing, as the cold grip of the ice took hold? Genetic tracing can and does fit the archaeological record of that time rather nicely, but it also tells us something much more relevant and general to European roots: that 80 per cent of modern European lines are essentially derived from ancestors who were present in Europe before the Big Freeze.
An important European maternal clan 'HV' spread from Eastern into Northern and Western Europe, perhaps heralding the beginning of the Early Upper Palaeolithic 33,000 years ago. The HV clan is now widespread and fairly evenly distributed in Europe. H is the single, commonest line of all. It was not always so, and a specific sister cluster of the H clan, V, who were probably born in the Basque country, tells us why. The archaeology shows us how the south-western refuge of the Basque country drew cultures and presumably people down from north-west Europe during the lead-up to the Ice Age. Since Western Europe is separated from Italy by mountains, we would expect the reverse process after the Ice age as people re-expanded again from the Basque country and north along the Atlantic coast. This is exactly the picture left by the post-glacial spread of the maternal subgroup V, which has its highest frequency, diversity, and age in the Basque country, falling off as one goes north and only present in rather low frequencies in Italy. V arose in the Basque country shortly after the LGM. Her pre-V ancestor has been dated to 26,400 years ago, long before the LGM. Pre-V is still found farther east in the Balkans and Trans-Caucasus, consistent with her ultimate eastern origin. Even the post-glacial dates of expansion of V (16,300 years in the west) fit this scenario. Exactly the same pattern was seen for the Y-chromosome marker Ruslan, who we saw had moved into northern Europe from the east and found his home in Northern and Western Europe. The present-day picture shows Ruslan at his maximum frequency of 90 per cent in the Spanish Basque country, with the next-highest rates in Western and Northern Europe.
Italy, on the other hand, capped as it is by the Alps, was less a refuge for northern populations than a temperate region of continuous occupation by Mediterranean folk present from before the LGM. This is reflected again in the high proportion (over one-third of the total) of persisting preglacial mtDNA lines found in that region. We can see from these examples that the refuge zones are characterized by dramatic expansions of lines born locally in the refuge zones during the LGM, and also by high rates of persisting lines left over from the preglacial period. The latter pattern is certainly a feature of the Ukraine refuge, which as predicted by the archaeology retains 31 per cent of its preglacial maternal lines. A slightly less convincing case can be made for south-eastern Europeand the Balkans, which retained 24â26 per cent of preglacial lines.
It should be clarified that just because 20â34 per cent of modern European mtDNA lines have been retained from before the LGM, that does not mean that the rest of the lines found today had to have entered Europe from outside after the LGM. No, they were mostly locals. Of all modern European lines, 55 per cent originated in the period just after the ice age (the Late Upper Palaeolithic) but these, like the V haplogroup, probably derived from pre-existing European lines and simply reflect the post-glacial re-expansions from the refuges â in other words, new shoots off an old stock. Real fresh immigration into Europe from the Near East during the Neolithic period (from 8,000 years ago onwards) perhaps accounts for only 15 per cent of modern lines.
An interesting recent discovery about the genetic make-up of the south-eastern European region has to do with Y chromosome markers in Romania. The Carpathian Mountains were glaciated during the Ice Age and thus formed an effective, jagged barrier between south-eastern Europe and the regions bordering the Black Sea. This barrier splits Romania in two from top to bottom. Without their ice, the Carpathians hardly constitute an insurmountable physical barrier today, but they still mark a clear genetic boundary. This is revealed by Y-chromosome markers characteristic of north-eastern Europe and the Ukraine occurring at higher rates to the east of the Carpathians, while the markers more characteristic of Central Europe are found to the west. But this micro-regional boundary is very much obscured by the great dominance of the main Eastern European Y lineage M17, which may characterize the original preglacial Eastern Gravettian intrusions from the east. This lineage is found at very high rates throughout Eastern Europe â from Poland, through Slovakia and Hungary, to the Ukraine. M17 is still found at high frequencies among the Slavic peoples of the Balkans, which could support the existence of the Balkan ice-age refuge.
Again, in Northern Asia, the genetic record tells us that these hardy hunters of the permafrost retained some of their ancient maternal lines from before the LGM, and that there were subsequent expansions of certain subgroups after the thaw. MtDNA lines A, C, and Z are characteristic of North Asia, while D also extends farther south in China. Of these lines, A clearly survived from well before the LGM, as did various M and N lines. Then there was a gap of 10,000 years until about 17,000 years ago, before the re-expansion of lines such as variants of D, A, C, and finally Z.
<b>The genetics of North and Central Asia has simply confirmed what we might expect from the archaeology: when it got cold, the hunters of the Mammoth Steppe shrank in range and hunkered down, and when it got warm again they bounced back and reexpanded. The more interesting questions are what they looked like, and who their closest local descendants are today. Why and when did Mongoloids become the dominant types throughout most of Asia and the Americas? Does the genetic story tell us anything that cannot be inferred from the archaeological record?</b>