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Thread: Did haplogroup I only develop after the Ice Age?

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    Did haplogroup I only develop after the Ice Age?

    Published data indicate that haplogroup I's most recent common ancestor was located in North West Europe, and that its population rapidly grew and diversified fairly shortly afterwards in this same location. Reproductive success like this would usually be expected to occur in promising locations, so this does not seem to be intuitively consistent with the theory that I initially expanded during the Ice Age, when much of its habitat was extremely cold and covered by glaciers. Nor does it seems consistent with these people originating pre-Ice Age and basing themselves in perma-frozen North West Europe for thousands of years until the ice sheets melted. Is it more likely that I's most recent common ancestor arrived and thrived in Europe soon after the Ice Age, just as the North West of the continent was becoming highly habitable and when it was largely empty, with little competition for resources?

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    Quote Originally Posted by epp View Post
    Is it more likely that I's most recent common ancestor arrived and thrived in Europe soon after the Ice Age..?
    No. Europe was not entirely deserted during the Last Glacial Maximum. There were pockets of people living in southern refuges. It was mainly these people who were able to expand to re-populate the more northerly parts of Europe. I don't say that absolutely no-one arrived from outside Europe as the climate improved. A few people probably came from the Levant along the coast to Greece. Others we know arrived from the Asian steppe. But a man of Y-DNA haplogroup I2a was buried in a cave in Switzerland in 13,560–13,770 cal. BP. http://www.ancestraljourneys.org/palaeolithicdna.shtml

    So it would appear that Y-DNA haplogroup I had arrived in Europe in or by the Gravettian period. The latest estimate from Y-Full of its age is 42,400 ybp (formation), and TMRCA 27,300 ybp. That is not old enough to have arrived with the very first Homo sapiens in Europe 45,000 years ago, but it could have arisen from an IJ father in Europe before the Ice Age made northern Europe uninhabitable around 20,000 years ago.

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    Quote Originally Posted by epp View Post
    Published data indicate that haplogroup I's most recent common ancestor was located in North West Europe, and that its population rapidly grew and diversified fairly shortly afterwards in this same location.
    Which study was this? I don't actually recall Northwest Europe ever being suggested as origin of Haplogroup I.

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    Quote Originally Posted by Jean M View Post
    No. Europe was not entirely deserted during the Last Glacial Maximum. There were pockets of people living in southern refuges. It was mainly these people who were able to expand to re-populate the more northerly parts of Europe. I don't say that absolutely no-one arrived from outside Europe as the climate improved. A few people probably came from the Levant along the coast to Greece. Others we know arrived from the Asian steppe. But a man of Y-DNA haplogroup I2a was buried in a cave in Switzerland in 13,560–13,770 cal. BP. http://www.ancestraljourneys.org/palaeolithicdna.shtml

    So it would appear that Y-DNA haplogroup I had arrived in Europe in or by the Gravettian period. The latest estimate from Y-Full of its age is 42,400 ybp (formation), and TMRCA 27,300 ybp. That is not old enough to have arrived with the very first Homo sapiens in Europe 45,000 years ago, but it could have arisen from an IJ father in Europe before the Ice Age made northern Europe uninhabitable around 20,000 years ago.
    This is an interesting study. Yes, I agree that Europe may not have been entirely deserted during the Last Glacial Maximum, but I have doubts whether those present would have been haplogroup I:
    1. All haplogroup I currently in possible Southern European refuge locations is of relatively recent origin. For this to be compatible with evidence from current samples, you would have to accept that haplogroup I expanded and diverged in Northern Europe, migrated en masse to Southern Europe during the Ice Age, then over ten thousand years later, all migrated back to Northern Europe again en masse, leaving no remaining trace of themselves in southern European populations. My view is that this is implausible.
    2. The man buried in the Swiss cave was not proven I2a - the researcher merely described I2a as his "best guess".
    3. The cave in question is not in a Southern refuge, but North of the Alps, near the source of the Northern River Rhine, where current DNA samples suggest some of the earliest haplogroup I development occurred.
    4. The body in the study was carbon-dated at 9,850 BC, which is not before or during the Ice Age, but after it had finished.

    In my view, the evidence seems most consistent with I arriving in North Western Europe from the East after the Ice Age had come to an end.

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    Quote Originally Posted by epp View Post
    For this to be compatible with evidence from current samples, you would have to accept that haplogroup I expanded and diverged in Northern Europe.
    What makes you think that haplogroup I expanded and diverged in Northern Europe? Modern DNA cannot tell us that.
    Last edited by Jean M; 01-23-2016 at 05:17 PM.

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    Quote Originally Posted by Megalophias View Post
    Which study was this? I don't actually recall Northwest Europe ever being suggested as origin of Haplogroup I.
    Just to clarify, I'm not suggesting that haplogroup I originated in North West Europe, rather that North West Europe is the likely location for the most recent common ancestor of its surviving lineages.
    It would be quite surprising if no one had suggested North West Europe before, as the data freely available on the internet seems to indicate it fairly clearly - the most diverse I1 samples are found in this region, and the most diverse I2 samples are also found in this region.

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    Quote Originally Posted by Jean M View Post
    What makes you think that haplogroup I expanded and diverged in Northern Europe? Modern DNA cannot tell us that.
    In the absence of other reliable information, I am assuming that haplogroup I is most likely to have diverged where it is currently at its most diverse.

    I'd be grateful if you would let me know whether you think I have correctly analysed the the study of the body in the Swiss cave.

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    Quote Originally Posted by epp View Post
    In the absence of other reliable information, I am assuming that haplogroup I is most likely to have diverged where it is currently at its most diverse.
    Geneticists used to claim that it was most diverse today in southeastern Europe, but in any case this methodology is problematic.

    Yes geneticists developed the theory that that where they find the greatest genetic variance of a haplogroup is likely to be its point of origin, since the longer a lineage has been in a place, the longer it has had to accumulate variations. This seems satisfactory in broad continental outline, but later movements will have swirled the mix in ways that could mislead us if we expect variance today to exactly match that in prehistory. A present-day population could have acquired diversity from diverse waves of immigrants. We find a high variance within European haplogroups in the United States of America, but we know full well that these haplogroups do not have their origin there. So variance is most convincing when supported by other kinds of evidence.

    Take archaeology. There was no-one living in Northern Europe when it was covered by ice sheets. So everyone living today in Scandinavia and the British Isles descends from people who arrived there in the Mesolithic at the earliest. (We now know that later migrations had a huge impact on the gene pool.) The pattern of diversity in Y-DNA I that we see in living people today cannot reflect an origin point in northern Europe before the LGM.

    I2 was present in Scandinavia in the Mesolithic, but not the I1 that is more common there today.
    I1 and I2 were both present in Neolithic Hungary.
    The expansion of I1 in Scandinavia is compatible with an arrival in the Copper/Bronze Age.
    The expansion of I2a1b2a in the Balkans is compatible with the arrival of Slavs in the early medieval period. There they might encounter the occasional I2a that descended from Neolithic farmers there, so creating diversity.
    Last edited by Jean M; 01-23-2016 at 06:26 PM.

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    Here is Ken Nordtvedt's conjectural map of the spread of branches of haplogroup I, as created in 2011. I apologise in advance to Ken for using something of his that is several years out of date, but I have nothing more recent.

    Nordtvedt2011HgIspread.jpg

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    I used to have an online page on haplogroup I, but did not have time to maintain it in the face of the deluge of data in recent years, so I took it down. However here's the gist of relevant bits:

    Ancient DNA is gradually resolving the mysteries of Y-DNA Haplogroup I (L41). Its modern distribution was puzzling. On the one hand it seemed ancient in Europe. It rarely appears outside the boundaries of Europe and European colonies. So it was not a good candidate for arrival with farmers from the Near East. Nor did it seem the prime candidate for spread with the Indo-Europeans, since they travelled both west into Europe and east into the Indian Subcontinent. So the natural conclusion was that haplogroup I had been stalking around Europe since the Stone Age. On the other hand the pattern of I subclades in present-day European men look relatively recent. We see regional bunching, typical of relatively recent arrivals. What are we to make of these contradictions? The haplogroup may date deep into the distant European past, but it seems that most of the hunters and foragers who carried it have no direct descendants in the male line today.

    Population patterns

    In a hunter-gatherer economy, the population is usually maintained at replacement level, where that community remains within a particular territory. Women space births by weaning late. Population levels need to be low, as each hunting band needs to roam a large territory. The human population dropped dramatically world-wide during the last glacial maximum. Within Europe it fell to the point where we would today classify it as an endangered species.

    Then the population expanded during the Mesolithic as people gradually reclaimed the territory that had been lost to the climate downturn. Once it had expanded enough to fill the territory at the low hunter-gatherer level, we would expect it to be stable until farming made higher levels possible. Haplogroup I1 does not show any star-burst of subclades at that time, so we can presume that people carrying it were in no hurry to take up farming. However we do see bursts of new lineages in I2 at c. 8,000 years ago = 6000 BC, as farming reached the Balkans. It appears that some I2 men were willing and able to adopt agriculture.

    So my inclination is to look for the ancestors of today's I-men in successful hunter-gatherer cultures, which had a good chance of leaving descendants. In the days when all mankind lived by hunting and gathering, all could be considered equally successful if they managed to survive in competition with other predators. This might include other human hunting bands, but fellow humans were not initially the main competition. Man had to be clever enough to out-do lions and bears and not end up at the wrong end of the food chain. Once farming entered the picture, hunters were in direct competition with people who could outbreed them and inexorably take over the territory. Successful hunting cultures at that point were few and far between. Characteristically they occupied a highly fruitful hunting or fishing niche, that could scarcely be bettered at that stage by turning it over to farming. People in such a niche could hold off any incoming farmers who thought otherwise, and choose to adopt whatever seemed useful from farming neighbours at their own pace.

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