Icae Age European population botleneck

[Duncan Head]

Note that the Ice Age "bottleneck" is specifically a collapse of the European population. Nothing that I am aware of suggests a similar decline elsewhere. I am not quite sure why we need to look at causes other than the cold and the glaciation itself for the population crash.

What caused the glaciation is I think unknown; changes in the amount of sunlight received, either because of changes in solar output or because of wobbles in the Earth's orbit, seem to be the most popular explanation, but AFAIK the question is still open. Volcanism is a candidate for decades- or even centuries-long cool periods like the Early Modern "little ice age", but not I think for the longer and colder "real" ice ages.

[Patrick Waterson]

Note that the Ice Age "bottleneck" is specifically a collapse of the European population. Nothing that I am aware of suggests a similar decline elsewhere.

Perhaps because of a lack of similar studies elsewhere?

I am not quite sure why we need to look at causes other than the cold and the glaciation itself for the population crash.

Would not glaciation be more likely to cause a population migration to warmer and more fertile lands rather than a several orders of magnitude population contraction in situ?  ["How's the ice doing, dear?"  "It's half-way up the garden now."  "Don't you think we ought to consider moving?"  "Nah, just sit here and let it crunch over us."]

What caused the glaciation is I think unknown; changes in the amount of sunlight received, either because of changes in solar output or because of wobbles in the Earth's orbit, seem to be the most popular explanation, but AFAIK the question is still open. Volcanism is a candidate for decades- or even centuries-long cool periods like the Early Modern "little ice age", but not I think for the longer and colder "real" ice ages.

Agreed: there just does not seem to be enough cooling power in volcanism, at least volcanism as we know it.  It would seem to require a disruptive agency out of the oridinary.

One thought: much ice age theory and many assumptions regarding the extent of ice sheet coverage are based on the interpretation of scoured valleys and terminal moraines as glacial in nature.  Since such features are found at latitudes up to and including the equator, a certain amount of doubt about their actually being the work of ice sheets seems warranted.  (Anyone remember the 'snowball Earth' theory?)  Waves of translation would leave similar traces, and may be a preferable explanation for many of these features.  This in turn would shorten the presumed duration of 'ice ages' as a wave of translation could scour a valley in half an hour whereas an ice sheet would take several hundred years.

So there may not have been anything like the extent of glaciation assumed; the reason I raise this is because whereas gradual progress of ice sheets would tend to displace rather than annihilate populations, waves of translation would provide a massive body count and considerable population contraction in a very short time.

Which still does not provide a cause for the whole thing ...

[Swampster]

Note - the researcher does say that there may be gene lines which simply died out - we may be seeing something of a Genghis factor.

If a cataclysm was involved...
With the Laki eruption, 80% of the sheep died. The cattle and horses had a lower mortality but this may be down to being kept indoors and/or receiving stored fodder.
If regions of Ice Age Europe had anything like the same rate of mortality for the animals then the human population will suffer from lack of prey and probably damage to forage, not having stocks of food from previous seasons nor the ability to import. Most will not be in a convenient place to fish sufficiently to make much difference. Whether cooperation between groups had become as advanced as is now thought for some of the Neolithic period, competition for resources would cause the demise or driving out of groups. If these establish themselves further south then they have little need to return, allowing those who remained to repopulate with their own gene lines.

I wonder if there has been any links done between this study and the recent Basque findings. http://www.bbc.co.uk/news/science-environment-34175224
They seem to have a higher than average relationship to early hunter gatherers though still mixed with early farmers, this mix happening quite some time after the Ice Age.

[valentinianvictor]

I'm almost afraid to mention here Graham Hancock's Dryas comet theory for the extinctions during the last ice age...

[Patrick Waterson]

If a cataclysm was involved...
With the Laki eruption, 80% of the sheep died. The cattle and horses had a lower mortality but this may be down to being kept indoors and/or receiving stored fodder.
If regions of Ice Age Europe had anything like the same rate of mortality for the animals then the human population will suffer from lack of prey and probably damage to forage, not having stocks of food from previous seasons nor the ability to import. Most will not be in a convenient place to fish sufficiently to make much difference. Whether cooperation between groups had become as advanced as is now thought for some of the Neolithic period, competition for resources would cause the demise or driving out of groups. If these establish themselves further south then they have little need to return, allowing those who remained to repopulate with their own gene lines.

But the history of Europe is, or is considered to be, largely a history of periodic migrations.  Would not these migrations themselves also have to be derived from a very small survivor base for there to be an observable DNA 'bottleneck'?

Competition for diminished resources would doubtless be quite intense, but the existence of such competition would of itself indicate a much higher population density than allowed for by the study.  We may note that despite their livestock losses and a concomitant decade of shortages, the population of Iceland bounced back without noticeable narrowing of the genetic base.  Events such as the Plague of Titus or the Black Death are estimated to have taken one third to one half of the human population, but their impact on human genetic diversity was minimal, even unnoticeable.  We are looking at something that wiped out perhaps 95-99% of the European population.

I'm almost afraid to mention here Graham Hancock's Dryas comet theory for the extinctions during the last ice age...

It may still be fashionable, at least in some quarters.

[Swampster]

What would the population loss have been in Iceland if they had no fishing, no imports and no fodder to get some livestock through at least the initial problems? With these, the population halved. Without these, the population could have been reduced by far, far more. The story of Norse Greenland could have been repeated in Iceland, but over an even shorter period.

I think part of the point of the article is that once a population declines sufficiently it is unlikely to survive. This is not a percentage issue but an absolute number. So while Iceland lost however many thousands, there were enough remaining and sufficiently in contact with each other to count as a single population, large enough to recover. The ice age model being suggested is that each group starts small and  so losses can take it below viability more easily. The suggested isolation of each group means that the population of the area is made up of a large number of groups of doubtful viability, many of which then fail.

[Patrick Waterson]

What would the population loss have been in Iceland if they had no fishing, no imports and no fodder to get some livestock through at least the initial problems? With these, the population halved. Without these, the population could have been reduced by far, far more. The story of Norse Greenland could have been repeated in Iceland, but over an even shorter period.

Indeed.  Which still leaves us with the question of what it would take to create such conditions over the whole of Europe.  The point about Iceland is that a single eruption (or even a dual eruption) had a barely perceptible effect on the population of Europe.

I think part of the point of the article is that once a population declines sufficiently it is unlikely to survive. This is not a percentage issue but an absolute number.

With due respect to the article writers, it is not so much an issue of numbers as of adaptability.  We see this in endangered animal populations which can recover from very small breeding numbers once conditions are suitable.

The ice age model being suggested is that each group starts small and so losses can take it below viability more easily. The suggested isolation of each group means that the population of the area is made up of a large number of groups of doubtful viability, many of which then fail.

The essential thrust of the article seems to be:

"By analysing the genomes of human remains, the researchers are able to gather demographic data and clues to potential population sizes.

Prof. Pinhasi's team has found that the genomes sequenced from hunter-gatherers from Hungary and Switzerland between 14 000 to 7 500 years ago are very close to specimens from Denmark or Sweden from the same period.

These findings suggest that genetic diversity between inhabitants of most of western and central Europe after the ice age was very limited, indicating a major demographic bottleneck triggered by human isolation and extinction during the ice age."

My question is: what reduced the population to this 'major demographic bottleneck' in the first place?  Professor Pinhasi has this opinion:

"He believes that early humans crossed the continent in small groups that were cut off while the ice was at its peak, then successively dispersed and regrouped over thousands of years, with dwindling northern populations invigorated by humans arriving from the south, where the climate was better."

What is not clear is how this would result in genomic straitjacketing if the populations were being 'invigorated by humans arriving from the south'.  The 'dwindling northern populations' would have to undwindle by themselves to keep their ancestry on the straight and narrow.

Out of interest, here is the known coverage for the 'Younger Dryas climate event'.  Africa is mostly not included, perhaps through lack of studies there, otherwise we would probably see a more regular oval shape.  I would draw the viewer's attention to the fact that the central part of the distribution is largely over the North Atlantic, almost as if the event emanated from the destruction of a continent there.

[valentinianvictor]

If a large body, be it a comet or asteroid did impact/explode above the Earth 12,000 years ago as postulated by some scientists and Graham Hancock, then that may well be the answer. From the evidence I have seen, from ice core samples as well as samples gathered from land free of ice, there is very good evidence an event of this type occurred, and it would have had a massive impact on the world as a whole.

[Dangun]

Are we being distracted by the figurative use of the word bottleneck?

While the word bottleneck implies a narrowing, and by analogy, a population decline, aren't there other ways of interpreting the fact in the article, "the genomes sequenced from hunter-gatherers from Hungary and Switzerland between 14 000 to 7 500 years ago are very close to specimens from Denmark or Sweden from the same period"?

It might be clearer in the full paper, but there are many ways of conceiving of a narrowing of diversity without a narrowing of population.

[Patrick Waterson]

It might be clearer in the full paper, but there are many ways of conceiving a narrowing of diversity without a narrowing of population.

A valid thought.  If there were, for example, a single Europe-spanning monoethnic culture at the time, this would provide lack of genetic diversity without requiring a vastly diminished population.

We do also have the widespread 'black mat' (charred nanodiamonds) distribution evidence for the Younger Dyas event, which seems to be (insofar as one can trust temporal estimates at this distance BC) close-ish in time.  The question is: does this event relate to the non-diverse European population, and if so, how?

[Dangun]

A valid thought.  If there were, for example, a single Europe-spanning monoethnic culture at the time, this would provide lack of genetic diversity without requiring a vastly diminished population.

Or perhaps later and faster than earlier-expected population expansion from a narrow base.
Or perhaps the mix of intra- and inter-population group breeding effects the results.
I have no idea, other than that there does seem to be a number of patterns which fit the data from this short article.