June 11, 2014

Craniometric discontinuity at the Last Glacial Maximum in Europe

The paper includes a craniometric dataset on 10 variables in the supplementary material.

Nature Communications 5, Article number: 4094 doi:10.1038/ncomms5094

Craniometric analysis of European Upper Palaeolithic and Mesolithic samples supports discontinuity at the Last Glacial Maximum

Ciaraán Brewster et al.

The Last Glacial Maximum (LGM) represents the most significant climatic event since the emergence of anatomically modern humans (AMH). In Europe, the LGM may have played a role in changing morphological features as a result of adaptive and stochastic processes. We use craniometric data to examine morphological diversity in pre- and post-LGM specimens. Craniometric variation is assessed across four periods—pre-LGM, late glacial, Early Holocene and Middle Holocene—using a large, well-dated, data set. Our results show significant differences across the four periods, using a MANOVA on size-adjusted cranial measurements. A discriminant function analysis shows separation between pre-LGM and later groups. Analyses repeated on a subsample, controlled for time and location, yield similar results. The results are largely influenced by facial measurements and are most consistent with neutral demographic processes. These findings suggest that the LGM had a major impact on AMH populations in Europe prior to the Neolithic.

Link

11 comments:

Vincent said...

Thanks for sharing, Dienekes.

The authors attribute the craniofacial differences they found between pre- and Post-LGM populations to the LGM and to the adaptive processes which might have taken place because of it. I am very skeptical about such a huge and so fast adaptive process and the possibility that it might have taken place in reality. In 2008 you shared with us another study (http://dienekes.blogspot.it/2008/11/differences-between-early-and-late.html?m=1) on the same subject. That study used other skeletal data besides craniometric data, and the conclusion to which the authors came is summed as follows: "While some of the changes observed can be explained through models of biocultural or environmental adaptation (e.g., decreased lower limb robusticity following decreased mobility; changes in body proportions along with climatic change), others are more difficult to explain. For instance, craniodental and upper limb robusticity show complex evolutionary patterns that do not always correspond to expectations. In addition, the marked decline in stature and the mosaic nature of change in body proportions still await clarifications."

My theory is that there was a population replacement immediately before the LGM ca. 23 kya. A population of Central Asian origin (presumably marked by Y-DNA I-M170) migrated into Europe and replaced almost completely the indigenous male population, at the same time taking indigenous women (mtDNA U and U8, according to recently analysed ancient DNA). This chain of events is similar to that of the spread of E-M2 throughout sub-Saharan Africa. E-M2 carriers were physically different from the indigenous sub-Saharan hunter-gatherers (marked by Y-DNA A and B) just like pre-LGM individuals were markedly different from post-LGM individuals. E-M2 spread very quickly and soon replaced most of the indigenous male population because its carriers were more numerous and technologically more advanced than the indigenous hunter-gatherers, just like Solutreans were more advanced and more numerous than Aurignacians/Gravettians (for the "more numerous" piece, see http://www.ohll.ish-lyon.cnrs.fr/pages/documents_Aussois_2005/pdf/Jean-Pierre_Bocquet-Appel.pdf). The only differences with what happened in Europe during the LGM is the presence of enclaves carrying the indigenous (pre-Bantu) Y-DNA haplogroups in sub-Saharan Africa but not in Europe (or at least not in a statistically significant way) and the absence of a critical climatic event which could have helped the population replacement during the Bantu expansion. In Europe, the only role of the LGM was to help the newcomers to wipe out the indigenous males.

sykes.1 said...

On the other hand, the Russian fox experiment showed that only about 20 generations is needed for substantial evolutionary change if the selection pressure is high enough. That's only 500 years in human terms.

http://en.wikipedia.org/wiki/Domesticated_silver_fox

eurologist said...

Vincent,

Interesting thoughts. However, I think a few thousand years can easily lead to the "appearance" of distinct morphological adaptations if these were already present in small numbers, and then selected for. So, as long the original population was sufficiently diverse, all bets are of.

A reversal is equally possible as long as the population size remains sufficiently large. It is hard to get the full spectrum of phenotypes in limited data*.

In my view, the largest (and best-documented) impact on Europe after the Aurignacian is obviously the Gravettian, which not only affected N and W Europe directly, but in my view pushed other groups with different haplogroups out of the Upper Indus River area south and into the Near-East via a more southerly route. A double-whammy, so-to-speak, for SE Europe.

Based on known data, I can't see the Solutrean as an external force from the east.


* which is also why I really can't find much useful, in this study.

andrew said...

As Vincent notes, pre-LGM and post-LGM ancient mtDNA from Paleolithic modern humans is more or less identical, which is surprising given that the modern human residents of Europe almost all died or fled to a handful of refugia during the LGM prior to repopulating Europe.

The crainometry data confirms that there is more to the story because there are physical anthropology differences between the "before" and "after" populations.

The repopulation of Europe after the LGM is also a plausible way to explain why Europeans who co-existed with Neanderthals for ca. 10,000-20,000 more years than Asians don't have higher Neanderthal admixture percentages than Asians (indeed, they have perhaps slightly less).

It would be very helpful to know more about the Y-DNA and autosomal DNA of the 45,000 years old West Eurasian who was recently genotyped to see if that could better frame our understanding of the pre-LGM v. post-LGM differences in modern human population genetics.

The little we do know is certainly not sufficient for me to take Vincent's suggestion of a dramatic Y-DNA I population replacement immediately pre-LGM without some examples of ancient Y-DNA that is non-hg I men in Europe pre-LGM.

Fanty said...

Skulls arent the only thing that had been different in paleolithic and mesolithic Europe. Also other things like bodysize and the difference between the sexes.

Paleolithic Europeans are taller and more robust than mesolithic Europeans, who are taller and more robust than neolithic Europeans.

Also there is a puzzelling difference between the two sexes.

In paleolithic Europe, females had been taller and more robust than the males. (WTF?)
Both stand taller than 21th century humans.

In mesolithic Europe, both sexes had been equally robust and equally tall.
Both are about as tall as 21th century European males.

In neolithic Europe the males are taller and more robust than the females.
The males are as tall (small) as medieval European males. (Whoever saw original plate armour can imagine how small that is. ;-)

Justin said...

Fanty, I am really curious about your first comment about the females being larger than the males; can you supply a source??

Vincent said...

"In my view, the largest (and best-documented) impact on Europe after the Aurignacian is obviously the Gravettian, which not only affected N and W Europe directly, but in my view pushed other groups with different haplogroups out of the Upper Indus River area south and into the Near-East via a more southerly route. A double-whammy, so-to-speak, for SE Europe."

Gravettians were still physically very similar to Aurignacians in most traits. Svaboda (2007) suggests a Levantine origin for the Gravettian on the basis of similarity in lithic technology, and proposes that Gravettian may have originated from the Ahmarian.

"Based on known data, I can't see the Solutrean as an external force from the east."

Yeah, but physical anthropology tells another story: Solutreans (during and after LGM) were very different from Gravetto-Aurignacians (pre-LGM).

Paul White said...

So frustrating... How difficult and time-consuming would it be to get DNA analysis on a decent sub-sample of these skulls?

Annie Mouse said...

Personally I don't rate skull and bone studies. IMO they oare of very limited value. They are too influenced by diet and cultural facters (eg birthing procedures, standards of beauty/status). You have only to see dramatic skull/size variations in Iberian women over short spaces of time to understand this. There is no way this was genetic. Diet and and culture.

eurologist said...

Annie,

I agree with you.

J. Lyon Layden said...

I pretty much agree with Vincent. Classic cro-magnons may not have even been in our current genome. If we ever get dna from them we might find they are closer to mungo mans genome, who wasa 6'6 big brained woman with more gracile features than kow swamp.
Also if you have a prehistoric giant hybrid brain that doesnt prepare itself well in the sun, the sweep of microcephaline d and aspm d might bring those brains down to modern size and make them beter suited for life AFTER the ice age.