The Original Industrial Revolution

Cro-Magnon woman (Wikicommons) – At northern latitudes, women had fewer opportunities for food gathering, so they were free to specialize in new and more cognitively demanding tasks, like garment making, needlework, weaving, leatherworking, pottery, and kiln operation.





I've published an article on the theory that cold Paleolithic winters selected for intelligence. This theory is often attributed to J. Philippe Rushton and Arthur Jensen but actually goes much further back. The article is open access (see link), and the abstract is provided below. Comments are welcome.




Rushton and Jensen argued that cognitive ability differs between human populations. But why are such differences expectable? Their answer: as modern humans spread out of Africa and into northern Eurasia, they entered colder and more seasonal climates that selected for the ability to plan ahead, in order to store food, make clothes, and build shelters for winter. This cold winter theory is supported by research on Paleolithic humans and recent hunter-gatherers. Tools become more diverse and complex as effective temperature decreases, apparently because food has to be obtained during limited periods and over large areas. There is also more storage of food and fuel and greater use of untended traps and snares. Finally, shelters have to be sturdier, and clothing more cold-resistant. The resulting cognitive demands are met primarily by women because the lack of opportunities for food gathering pushes them into more cognitively demanding tasks, like garment making, needlework, weaving, leatherworking, pottery, and kiln operation. The northern tier of Paleolithic Eurasia thus produced the "Original Industrial Revolution"—an explosion of creativity that preadapted its inhabitants for later developments, i.e., farming, more complex technology and social organization, and an increasingly future-oriented culture. Over time, these humans would spread south, replacing earlier populations that could less easily exploit the possibilities of the new cultural environment. As this environment developed further, it selected for further increases in cognitive ability. Indeed, mean intelligence seems to have risen during recorded history at temperate latitudes in Europe and East Asia. There is thus no unified theory for the evolution of human intelligence. A key stage was adaptation to cold winters during the Paleolithic, but much happened later.



Reference



Frost, P. (2019). The OriginalIndustrial Revolution. Did Cold Winters Select for Cognitive Ability? Psych 2019, 1(1), 166-181

https://doi.org/10.3390/psych1010012

Did cold seasonal climates select for cognitive ability?

Paleolithic artefacts (Wikicommons). The northern tier of Eurasia saw an explosion of creativity that pre-adapted its inhabitants for later developments.

The new journal Psych will be publishing a special follow-up issue on J. Philippe Rushton and Arthur Jensen's 2005 article: "Thirty Years of Research on Race Differences in Cognitive Ability." The following is the abstract of my contribution. The article will appear later.

The first industrial revolution. Did cold seasonal climates select for cognitive ability?

Peter Frost

Abstract: In their joint article, Rushton and Jensen argued that cognitive ability differs between human populations. But why are such differences expectable? Their answer: as modern humans spread out of Africa and into the northern latitudes of Eurasia, they entered colder and more seasonal climates that selected for the ability to plan ahead, since they had to store food, make clothes, and build shelters for the winter. 

This explanation has a long history going back to Arthur Schopenhauer. More recently, it has been supported by findings from Paleolithic humans and contemporary hunter-gatherers. Tools become more diverse and complex as effective temperature decreases, apparently because food has to be obtained during limited periods of time and over large areas. There is also more storage of food and fuel and greater use of untended traps and snares. Finally, shelters have to be sturdier, and clothing more cold-resistant. The resulting cognitive demands fall on both men and women. Indeed, because women have few opportunities to get food through gathering, they specialize in more cognitively demanding tasks like garment making, needlework, weaving, leatherworking, pottery, and use of kilns. The northern tier of Paleolithic Eurasia thus produced the "first industrial revolution"—an explosion of creativity that pre-adapted its inhabitants for later developments, i.e., agriculture, more complex technology and social organization, and an increasingly future-oriented culture. Over time these humans would spread south, replacing earlier populations that could less easily exploit the possibilities of the new cultural environment. 

As this cultural environment developed further, it selected for further increases in cognitive ability. In fact, mean intelligence seems to have risen during historic times at temperate latitudes in Europe and East Asia. There is thus no unified theory for the evolution of human intelligence. A key stage was adaptation to cold seasonal climates during the Paleolithic, but much happened later.

https://www.mdpi.com/journal/psych/special_issues/race_differences_cognitive_ability

References

Rushton, J.P. and A.R. Jensen. (2005). Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law 11(2): 235-294.

http://philipperushton.net/wp-content/uploads/2015/02/Thirty-Years-of-Research-on-Race-Differences-in-Cognitive-Ability-2005-by-John-Philippe-Rushton-Arthur-Robert-Jensen.pdf

A look at an early European

 

Kostenki Man, reconstructed by Mikhail Gerasimov (1907-1970). An early European who was not yet phenotypically European.

 

Who were the first Europeans? We now have a better idea, thanks to a new paper about DNA from a man who lived some 38,700 to 36,200 years ago. His remains were found at Kostenki, a well-known Upper Paleolithic site in central European Russia (Seguin-Orlando et al., 2014).

Kostenki Man tells us several things about the first Europeans and, more broadly, the first non-African humans:

The Neanderthal encounter

Modern humans received their Neanderthal admixture when they were just spreading out of Africa some 54,000 years ago. At that time, they had not yet encountered the Neanderthals and were entering the territory of the Skhul/Qafzeh hominids, a semi-archaic people of the Middle East. So we may have got our Neanderthal admixture indirectly. The Skhul/Qafzeh hominids had probably interbred with their Neanderthal neighbors to the north, and our ancestors may have then picked up this admixture while in the Middle East. 

When our ancestors spread farther north into Europe, some 45,000 to 42,000 years ago, they could have interbred directly with Neanderthals, but they didn't. Perhaps the two groups were just too different. They seem to have intermixed only via a third party that was neither fully modern nor fully archaic.

A strange detour ... and then another!

There was initially a large continuous population across northern Eurasia, perhaps composed of nomads who pursued wandering herds of reindeer across the European Plain and its eastward extension into central and northern Asia.

Not long before the time of Kostenki Man, these Northern Eurasians began to split into three regional groups: Western Eurasians, Eastern Eurasians, and the ancestors of Middle Eastern farmers. The degree of reproductive isolation is unclear, however, and gene flow may have continued between all three groups until the onset of the last ice age some 25,000 years ago. This may be why Kostenki Man does not fit perfectly into any of the three groups, although he is genetically closest to Western Eurasians.

Yes, Northern Eurasians were ancestral to the early farming peoples of the Middle East. It seems that early modern humans had to head north, learn to hunt reindeer, and then head south again before they could start farming. Sounds like a strange detour. Wouldn't it have been easier to stay put and do it locally? You know, Middle-Eastern hunter-gatherers becoming Middle Eastern farmers? Apparently not.

It gets even more convoluted. After some of those Northern Eurasians had gone south to the Middle East, some of their farming descendants "returned" to Europe and partially replaced its hunter-gatherers, particularly in southern and central Europe. This second detour has been greeted with disbelief. Dienekes (2014), for instance, has written: "I don't think many archaeologists would derive European farmers from Russia (Russia is actually one of the last places in Europe that became agricultural)."

True, but farming requires a mindset that may have come from those northern hunters (Frost, 2014). When Piffer (2013) looked at human variation in alleles at COMT, a gene linked to executive function, working memory, and intelligence, he found that northern hunting peoples had more in common with farming peoples than with other hunter-gatherers, "possibly due to the higher pressure on technological skills and planning abilities posed by the adverse climatic conditions."

That mindset made farming possible, but the first steps toward farming could not be taken in a cold climate. They had to be taken in a place with a long growing season and a wide variety of domesticable plants and animals, such as in the Middle East. Once farming had developed there, it could move back north, while taking along its technologies, its food crops, and its livestock species. 

Farming can develop in the tropics with a "tropical" mindset, but it looks very different. The farming that arose in West Africa is overwhelmingly women's work and seems to have wholly developed out of female plant gathering. The guinea fowl is the only animal that has been domesticated for food consumption in sub-Saharan Africa.

The Ice Age was not so bad 

The Upper Paleolithic humans of northern and eastern Europe did not die out during the last ice age, as was commonly thought. They survived the glacial maximum intact.

The European phenotype came later

Kostenki Man was dark-skinned, dark-eyed, and rather short. These details, curiously enough, appear not in the paper but in a review of the paper, published by the same journal, as well as in an interview with one of the authors (Associated Press, 2014; Gibbons, 2014). 

So we now have an upper bound for the emergence of the European phenotype, i.e., light skin and a diverse palette of hair and eye colors. The lower bound has been set by the remains of a Swedish hunter-gatherer, dated to 8,000 years ago, who had the "European" allele for light skin at the gene SLC24A5 (Skoglund et al., 2014).

Conclusion

My main criticism centers on the dating to 38,700 - 36,200 years ago. At the Kostenki site, the radiocarbon dating used to be some 10,000 years younger. It was then recalibrated to an older range of dates when a layer of volcanic ash at the site was attributed to a volcano that had erupted in southern Italy some 39,000 years ago. This recalibration was initially controversial, but the controversy has since subsided (Sinitsyn and Hoffecker, 2006). I would not rule out a subsequent re-recalibration.

By retrieving ancient DNA from an early modern human, we have made a key advance in human paleogenetics, perhaps more so than by sequencing the Neanderthal genome. We again see that evolution did not slow down with the emergence of anatomically and behaviorally modern humans some 60,000 years ago. It actually began to speed up, as humans began to enter not only new natural environments but also new cultural environments of their own making.

 

References 

Associated Press (2014). DNA study dates Eurasian split from East Asians, The Columbus Dispatch, November 6

http://hosted2.ap.org/OHCOL/07e34bb59e064cedb7e2776e8db4b4f7/Article_2014-11-06-EU--Eurasian%20Split/id-ae36fa368c634c7383d807942bd5fe67 

Dienekes (2014). Genome of Kostenki-14, an Upper Paleolithic European (Seguin-Orlando, Korneliussen, Sikora, et al. 2014), Dienekes' Anthropology Blog, November 7

http://dienekes.blogspot.ca/2014/11/genome-of-kostenki-14-upper-paleolithic.html  

Frost, P. (2014). The first industrial revolution, Evo and Proud, January 18

http://evoandproud.blogspot.ca/2014/01/the-first-industrial-revolution.html 

Gibbons, A. (2014). European genetic identity may stretch back 36,000 years, Science, News, November 6

http://news.sciencemag.org/archaeology/2014/11/european-genetic-identity-may-stretch-back-36000-years 

Piffer, D. (2013). Correlation of the COMT Val158Met polymorphism with latitude and a hunter-gather lifestyle suggests culture-gene coevolution and selective pressure on cognition genes due to climate, Anthropological Science, 121, 161-171.

https://lesacreduprintemps19.files.wordpress.com/2014/01/correlation-of-the-comt-val158met-polymorphism-with-latitude-and-a-hunter-gather-lifestyle-suggests-culturee28093gene-coevolution-and-selective-pressure-on-cognition-genes-due-to-climate.pdf 

Seguin-Orlando, A., T.S. Korneliussen, M. Sikora, A.-S. Malaspinas, A. Manica, I. Moltke, A. Albrechtsen, A. Ko, A. Margaryan, V. Moiseyev, T. Goebel, M. Westaway, D. Lambert, V. Khartanovich, J.D. Wall, P.R. Nigst, R.A. Foley, M.M. Lahr, R. Nielsen, L. Orlando, and E. Willerslev. (2014). Genomic structure in Europeans dating back at least 36,200 years, Science, Published online 6 November 2014

http://www.sciencemag.org/content/early/2014/11/05/science.aaa0114
http://www2.zoo.cam.ac.uk/manica/ms/2014_Seguin_Orlando_et_al_Science.pdf  

Sinitsyn, A.A., and J.F. Hoffecker. (2006). Radiocarbon dating and chronology of the Early Upper Paleolithic at Kostenki, Quaternary International, 152-153, 164-174.

http://www.sciencedirect.com/science/article/pii/S1040618206000206 

Skoglund, P., H. Malmstrom, A. Omrak, M. Raghavan, C. Valdiosera, T. Gunther, P. Hall, K. Tambets, J. Parik, K-G. Sjogren, J. Apel, E. Willersley, J. Stora, A. Gotherstrom, and M. Jakobsson. (2014). Genomic diversity and admixture differs for stone-age Scandinavian foragers and farmers, Science, 344 (6185), 747-750.

http://www.sciencemag.org/content/344/6185/747.short

 

The riddle of Microcephalin

 

World distribution of the recent Microcephalin allele. The prevalence is indicated in black and the letter 'D' refers to the 'derived' or recent allele (Evans et al., 2005)

 

Almost a decade ago, there was much interest in a finding that a gene involved in brain growth, Microcephalin, continued to evolve after modern humans had begun to spread out of Africa. The 'derived' allele of this gene (the most recent variant) arose some 37,000 years ago somewhere in Eurasia and even today is largely confined to the native populations of Eurasia and the Americas (Evans et al., 2005).

Interest then evaporated when no significant correlation was found between this derived allele and higher scores on IQ tests (Mekel-Bobrov et al, 2007; Rushton et al., 2007). Nonetheless, a later study did show that this allele correlates with increased brain volume (Montgomery and Mundy, 2010).

So what is going on? Perhaps the derived Microcephalin allele helps us on a mental task that IQ tests fail to measure. Or perhaps it boosts intelligence in some indirect way that shows up in differences between populations but not in differences between individuals.

The second explanation is the one favored in a recent study by Woodley et al. (2014). The authors found a high correlation (r = 0.79) between the incidence of this allele and a population's estimated mean IQ, using a sample of 59 populations from throughout the world. They also found a correlation with a lower incidence of infectious diseases, as measured by DALY (disability adjusted life years). They go on to argue that this allele may improve the body’s immune response to viral infections, thus enabling humans to survive in larger communities, which in turn would have selected for increased intelligence:

Bigger and more disease resistant populations would be able to produce more high intelligence individuals who could take advantage of the new cognitive opportunities afforded by the social and cultural changes that occurred over the past 10,000 years. (Woodley et al., 2014)

Bigger populations would also have increased the probability of “new intelligence-enhancing mutations and created new cognitive niches encouraging accelerated directional selection for the carriers of these mutations.” A positive feedback would have thus developed between intelligence and population density:

[…] the evolution of higher levels of intelligence during the Upper Paleolithic revolution some 50,000 to 10,000 ybp may have been necessary for the development of the sorts of subsistence paradigms (e.g. pastoralism, plant cultivation, etc.) that subsequently emerged. (Woodley et al., 2014)

 

 
What do I think?

I have mixed feelings about this study. Looking at the world distribution of this allele (see above map), I can see right away a much higher prevalence in Eurasia and the Americas than in sub-Saharan Africa. That kind of geographic distribution would inevitably correlate with IQ. And it would also correlate with the prevalence of infectious diseases.

Unfortunately, such correlations can be spurious. There are all kinds of differences between sub-Saharan Africa and the rest of the world. One could show, for instance, that per capita consumption of yams correlates inversely with IQ. But yams don't make you stupid.

More seriously, one could attribute the geographic range of this allele to a founder effect that occurred when modern humans began to spread out of Africa to other continents. In that case, it could be junk DNA with no adaptive value at all. There is of course a bit of a margin between its estimated time of origin (circa 37,000 BP) and the Out of Africa event (circa 50,000 BP), but that difference could be put down to errors in estimating either date.

No, I don't believe that a founder effect was responsible. A more likely cause would be selection to meet the cognitive demands of the First Industrial Revolution, when humans had to create a wider range of tools to cope with seasonal environments and severe time constraints on the tasks of locating, processing, and storing food. This allele might have helped humans in the task of imagining a 3D mental “template” of whatever tool they wished to make. Or it might have helped hunters store large quantities of spatio-temporal information (like a GPS) while hunting over large expanses of territory. Those are my hunches.

I don't want to pooh-pooh the explanation proposed in this study. At times, however, the authors' reasoning seems more than a bit strained. Yes, this allele does facilitate re-growth of neural tissue after influenza infections, probably via repair of damaged DNA, but the evidence for a more general role in immune response seems weak. More to the point, the allele’s time of origin (39,000 BP) doesn't correspond to a time when humans began to live in larger, more sedentary communities. This was when they were still hunter-gatherers and just beginning to spread into temperate and sub-arctic environments with lower carrying capacities. Human population density was probably going down, not up. It wasn't until almost 30,000 years later, with the advent of agriculture, that it began to increase considerably.

The authors are aware of this last point and note in it their paper. So we come back to the question: what could have been increasing the risk of disease circa 39,000 BP? The authors suggest several sources of increased risk: contact with archaic hominins (Neanderthals, Denisovans), domestication of wolves and other animals, increasing population densities of hunter-gatherers, and contact by hunter-gatherers with new environments. Again, this reasoning seems to push the envelope of plausibility. Yes, Neanderthals were still around in 39,000 BP, but they had already begun to retreat and by 30,000 BP were extinct over most of their former range. Yes, we have evidence of wolf domestication as early as 33,000 BP, but livestock animals were not domesticated until much later. Yes, there was a trend toward increasing population density among hunter-gatherers, but this was not until after the glacial maximum, i.e., from 15,000 BP onward. Yes, hunter-gatherers were entering new environments, but those environments were largely outside the tropics in regions where winter kills many pathogens. So disease risk would have been decreasing.

I don’t wish to come down too hard on this paper. There may be something to it. My fear is simply that it will steer researchers away from another possible explanation: the derived Microcephalin allele assists performance on a mental task that is not measured by standard IQ tests.

 

References 

Evans, P. D., Gilbert, S. L., Mekel-Bobrov, N., Vallender, E. J., Anderson, J. R., Vaez-Azizi, L. M., et al. (2005). Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans, Science, 309, 1717-1720.

http://www.fed.cuhk.edu.hk/~lchang/material/Evolutionary/Brain%20gene%20and%20race.pdf  

Mekel-Bobrov, N., Posthuma, D., Gilbert, S. L., Lind, P., Gosso, M. F., Luciano, M., et al. (2007). The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence, Human Molecular Genetics, 16, 600-608.

http://psych.colorado.edu/~carey/pdfFiles/ASPMMicrocephalin_Lahn.pdf  

Montgomery, S. H., and N.I. Mundy. (2010). Brain evolution: Microcephaly genes weigh in, Current Biology, 20, R244-R246.

http://www.sciencedirect.com/science/article/pii/S0960982210000862  

Rushton, J. P., Vernon, P. A., and Bons, T. A. (2007). No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism, Biology Letters, 3, 157-160.

http://semantico-scolaris.com/media/data/Luxid/Biol_Lett_2007_Apr_22_3(2)_157-160/rsbl20060586.pdf  

Woodley, M. A., H. Rindermann, E. Bell, J. Stratford, and D. Piffer. (2014). The relationship between Microcephalin, ASPM and intelligence: A reconsideration, Intelligence, 44, 51-63.

http://www.sciencedirect.com/science/article/pii/S0160289614000312  

Replacement or continuity?

 

Inuit meat cache, Kazan River (source: Library and Archives Canada / PA-101294). Because of their high meat diet, hunters produce more body heat than farmers do. Natural selection has thus favored certain mtDNA sequences over others in humans with this profile of heat production. A change in selection pressure may therefore explain, at least in part, the genetic divide between late hunter-gatherers and early farmers in Europe.

 

Who were the ancestors of present-day Europeans? The hunter-gatherers of the Paleolithic and the Mesolithic? Or the Neolithic farmers who began to spread out of the Middle East some 10,000 years ago?

This debate has teetered back and forth for the past thirty years. On the basis of various genetic polymorphisms, L.L. Cavalli-Sforza and his students argued that Europeans are largely descended from Middle Eastern farmers (Ammerman and Cavalli-Sforza, 1984; Cavalli-Sforza et al., 1994). On the basis of mtDNA and Y chromosomal data, two other research teams, one led by Martin Richards and the other by Ornella Semino, maintained that the European gene pool is over 75% of native hunter-gatherer origin (Richards et al., 2000; Semino et al., 2000). If we look only at the present-day gene pool, Europeans seem far too differentiated to be the descendants of Neolithic farmers from the Middle East.

Over the last few years, new evidence has swung the debate back to the model of population replacement. By retrieving DNA from ancient skeletal remains, we can now compare the latest hunter-gatherers with the earliest farmers, and what we see is a sharp genetic divide between the two (Bramanti et al., 2009). The farmers seem to have been immigrants who replaced the hunter-gatherers. This is direct evidence, so what more is there to say? Facts are facts.

Yet there is always more to say. Facts may be illusory or, if real, wrongly interpreted. For one thing, wherever we have a fairly continuous time series of ancient DNA, the genetic divide no longer appears between the latest hunter-gatherers and the earliest farmers. It appears between the earliest farmers and somewhat later farmers. This is particularly so when we examine haplogroup U lineages, whose disappearance is widely seen as evidence for population replacement. According to a study of 92 Danish remains, these lineages remained common after the Neolithic and reached their current low prevalence only during the Early Iron Age (Melchior et al., 2010).

If this genetic divide is not solely due to population replacement, what else might be responsible? Mishmar et al. (2003) were the first to suggest natural selection:

Thus, extensive global population studies have shown that there are striking differences in the nature of the mtDNAs found in different geographic regions. Previously, these marked differences in mtDNA haplogroup distribution were attributed to founder effects, specifically the colonizing of new geographic regions by only a few immigrants that contributed a limited number of mtDNAs. However, this model is difficult to reconcile with the fact that northeastern Africa harbors all of the African-specific mtDNA lineages as well as the progenitors of the Eurasia radiation, yet only two mtDNA lineages (macrohaplogroups M and N) left northeastern Africa to colonize all of Eurasia (1, 2) and also that there is a striking discontinuity in the frequency of haplogroups A, C, D, and G between central Asia and Siberia, regions that are contiguous over thousands of kilometers. Rather than Eurasia and Siberia being colonized by a limited number of founders, it seems more likely that environmental factors enriched for certain mtDNA lineages as humans moved to the more northern latitudes.

[...] We now hypothesize that natural selection may have influenced the regional differences between mtDNA lineages. This hypothesis is supported by our demonstration of striking differences in the ratio of nonsynonymous (nsyn)/synonymous (syn) nucleotide changes in mtDNA genes between geographic regions in different latitudes. We speculate that these differences may reflect the ancient adaptation of our ancestors to increasingly colder climates as Homo sapiens migrated out of Africa and into Europe and northeastern Asia.

This hypothesis has since received support from Balloux et al. (2009):

We show that populations living in colder environments have lower mitochondrial diversity and that the genetic differentiation between pairs of populations correlates with difference in temperature. These associations were unique to mtDNA; we could not find a similar pattern in any other genetic marker. We were able to identify two correlated non-synonymous point mutations in the ND₃ and ATP6 genes characterized by a clear association with temperature, which appear to be plausible targets of natural selection producing the association with climate. The same mutations have been previously shown to be associated with variation in mitochondrial pH and calcium dynamics. Our results indicate that natural selection mediated by climate has contributed to shape the current distribution of mtDNA sequences in humans.

Humans have to adapt to two sources of warmth: climate and internal body heat, which in turn varies with lifestyle and diet. Diet in particular results in different patterns of body heat production between hunter-gatherers and farmers, as explained by Speth (1983):

One aspect of protein metabolism relevant to this issue concerns the high "specific dynamic action" (SDA) of protein ingestion. The SDA of food refers to the rise in metabolism or heat production (diet-induced thermogenesis) resulting from the ingestion of food [...] The SDA of a diet consisting largely of fat is about 6- 14%, while that of a diet high in carbohydrates is about 6%. In striking contrast, the SDA of a diet consisting almost entirely of protein may be as high as 30%; or, in other words, for every 100 calories of protein ingested, up to 30 calories are needed to compensate for the increase in metabolism. Thus, persons whose diets are high in protein experience higher metabolic rates than those whose diets are composed largely of carbohydrate. For example, members of Eskimo populations, at least 90% of whose caloric needs were traditionally met by meat and fat (cf. Draper 1980:263; Hoygaard 1941), had basal metabolic rates 13 to 33% above the DuBois standard, which is based on the metabolic rates of populations consuming western diets (Itoh 1980:285).

Conclusion

Before ancient DNA became available, the prehistory of populations had to be inferred. The age of a genetic lineage was inferred from the degree of differentiation divided by the mutation rate. Since both variables could be known only approximately, the time depths of Europe's genetic lineages were likewise known only approximately.

Ancient DNA seems to promise a clearer picture because the only source of uncertainty is the age of the skeletal material. Unfortunately, this new method is more sensitive to uncertainty from another source: natural selection. Late hunter-gatherers and early farmers had to adapt to different environments. There certainly was a genetic divide between the two, but did it result from differences in origin or from differences in natural selection?

Natural selection distorts the picture if either method is used, since both assume that mtDNA is selectively neutral. The distortion is more serious, however, with the new method, which assumes selective neutrality across the genetic divide between late hunter-gatherers and early farmers—the very moment in prehistory when this assumption is most likely to fail. The old method assumes selective neutrality throughout the entire time depth of Europe’s genetic lineages—an assumption that may indeed be true over most of that time.

Even if the lineage has no selective value in and of itself, natural selection can still distort the picture. This is especially so for mtDNA:

Selection can change allele frequency even at a locus not responsible for fitness differences. Because there is little or no recombination in mitochondrial DNA, selection at one nucleotide affects the frequencies of all other variable nucleotides for the whole molecule. Selection on the nuclear genome, particularly nuclear-encoded proteins that are imported into the mitochondrion and X-linked markers that can have a high effective linkage to mtDNA, can also cause changes in the frequencies of mtDNA haplotypes. Equally importantly, selection on any other cytoplasmically inherited traits will directly affect the frequencies of mtDNA. (Ballard and Whitlock, 2004)

This is less of a problem with nuclear DNA because of recombination, but the problem remains if the presumably neutral gene is close to another gene of high selective value.

In raising these points, I am not trying to argue that Middle Eastern farmers made no contribution to the European gene pool. There is good archaeological evidence of these farmers pushing up the Danube and into central Europe. Elsewhere, however, the evidence for population replacement becomes weaker and the evidence for continuity correspondingly stronger. This is the conclusion that Zvelebil and Dolukhanov (1991) make with respect to northern and eastern Europe:

The transition to farming occurred very slowly and took a long time to complete, the whole process lasting 1500-4000 years. In the far north and northeast of Europe, the process was never completed. [...] Local hunter-gatherer societies played a significant role in the transition. There is strong evidence for continuity in material culture in most regions throughout the transition. Although this neither proves nor disproves the case for population movement associated with the transition (small groups of people could have migrated, leaving little or no trace in the archaeological record), such evidence does not support the colonization model for the transition to farming and it does indicate that local hunter-gatherer traditions were passed on from generation to generation during the long period of the adoption of farming.

And yet the advent of farming brought massive genetic change to northern and eastern Europe, including widespread decline of haplogroup U—the sort of change that is supposed to mean massive population replacement. Since farming began to spread to this region only 6,000 years ago, even later among the Finnish and Baltic peoples, there is only a very narrow time frame in which northern and eastern Europeans could have evolved their characteristic physical appearance, assuming of course that population replacement had actually happened.

Even in central Europe, where population replacement is well documented, we are still unsure whether it was permanent or temporary. Indeed, we see evidence of the replacers being later replaced, perhaps by natives who had never disappeared from the vicinity of the farming settlements (Haak et al., 2005; Rowley-Conwy, 2011).

 

References

Ammerman, A.J. and L.L. Cavalli-Sforza. (1984). The Neolithic Transition and the Genetics of Populations in Europe, New Jersey: Princeton University Press.

Ballard, J.W.O. and M.C. Whitlock. (2004). The incomplete natural history of mitochondria, Molecular Ecology, 13, 729-744.

http://dna.ac/filogeografia/PDFs/Ballard%26Whitlock_04_MTrev.pdf

Balloux F., L.J. Handley, T. Jombart, H. Liu, and A. Manica (2009). Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation. Proceedings. Biological Sciences, 276 (1672), 3447-55.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817182/?tool=pmcentrez

Bramanti, B., M. G. Thomas, W. Haak, M. Unterlaender, P. Jores, K. Tambets, I. Antanaitis-Jacobs, M.N. Haidle, R. Jankauskas, C.-J. Kind, F. Lueth, T. Terberger, J. Hiller, S. Matsumura, P. Forster, and J. Burger. (2009). Genetic discontinuity between local hunter-gatherers and Central Europe's first farmers, Science, 326 (5949), 137-140.

http://jsarf.free.fr/palanthsci/Europe's%20First%20Farmers%20Were%20Immigrants.pdf

Cavalli-Sforza, L.L., P. Menozzi, and A. Piazza. (1994). The History and Geography of Human Genes, New Jersey: Princeton University Press.

Haak, W., P. Forster, B. Bramanti, S. Matsumura, G. Brandt, M. Tänzer, R. Villems, C. Renfrew, D. Gronenborn, K.W. Alt, and J. Burger. (2005). Ancient DNA from the first European farmers in 7500-year-old Neolithic sites, Science, 310 (5750), 1016-1018.

http://www.sciencemag.org/content/310/5750/1016.short

Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7): e11898

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0011898#pone-0011898-g002

Mishmar, D., E. Ruiz-Pesini, P. Golik, V. Macaulay, A.G. Clark, S. Hosseini, M. Brandon, K. Easley, E. Chen, M.D. Brown, R.I. Sukernik, A. Olckers, and D.C. Wallace. (2003). Natural selection shaped regional mtDNA variation in humans, Proceedings of the National Academy of Sciences (USA), 100 (1), 171-176.

http://www.pnas.org/content/100/1/171.full

Richards, M., V. Macaulay, E. Hickey, E. Vega, B. Sykes, et al. (2000). Tracing European founder lineages in the Near Eastern mtDNA pool, American Journal of Human Genetics, 67, 1251-1276.

http://www.sciencedirect.com/science/article/pii/S0002929707629541

Rowley-Conwy, P. (2011). Westward ho! The spread of agriculturalism from Central Europe to the Atlantic, Current Anthropology, 52 (S4), S431-S451.

http://arkeobotanika.pbworks.com/w/file/fetch/48307263/Rowley-Conwy%2011%20CA%20Farming%20westward.pdf

Semino, O., G. Passarino, P.J. Oefner, A.A. Lin, S. Arbuzova, et al. (2000). The genetic legacy of Paleolithic Homo sapiens sapiens in extant Europeans: A Y chromosome perspective, Science, 290, 1155-1159.

http://fboekelo.tripod.com/boekelo/GP/semino.pdf

Speth, J.D. (1983). Energy source, protein metabolism, and hunter-gatherer subsistence strategies, Journal of Anthropological Archaeology, 2, 1-31.

http://faculty.ksu.edu.sa/archaeology/Publications/Hearths/Energy%20source,%20protein%20metabolism,%20and%20hunter-gatherer%20subsistence%20strategies.pdf

Zvelebil, M. and P. Dolukhanov. (1991). The transition to farming in Eastern and Northern Europe, Journal of World Prehistory, 5, 233-278.

http://link.springer.com/article/10.1007/BF00974991

The first industrial revolution

 

Eyed sewing needles from Ice Age Europe (17,000 to 10,000 BP). (source: Didier Descouens)

As early modern humans spread farther north, they entered more challenging environments. This was particularly so when they left the boreal forests and entered the open steppe-tundra that covered much of northern Eurasia. Food was plentiful but largely took the form of meat—herds of reindeer and other herbivores. With few plant foods to gather, women took on other tasks: meat processing, shelter building, and garment making. Men also had to make the most of their hunting successes, since no other food was available during lean times.

Necessity is the mother of invention. Northern hunting peoples had to create a wider range of new and complex tools, as well as mental simulations of how their actions would play out in the future:

The technology of recent hunter-gatherers is also influenced by temperature and diet. Both the diversity of tool types and the complexity of individual tools and weapons […] increase as effective temperature and the percentage of plant foods in the diet decline […]. This apparently reflects the need for greater foraging efficiency in habitats where resources are available for limited periods of time. Recent hunter-gatherers in cold environments also tend to make increased use of storage technologies and untended facilities (e.g., traps and snares). The former represent another adaptive response to seasonal variations in resource availability, while the latter reflect an efficient approach (i.e., reduced mobility) to collecting unpredictable and widely dispersed resources […]. Finally, modern hunter-gatherers in northern environments produce relatively complex technology for heat conservation and cold protection (e.g., tailored fur clothing). (Hoffecker, 2002, p. 10).

On the frozen steppe-tundra, each base camp became a center of activity for production, processing, and storage. Deep storage pits were dug into the permafrost for meat refrigeration. Hand-powered rotary drills made their appearance. We find “traces of fired ceramic technology, including remains of kilns heated to as much as 800 degrees C.” There is also evidence of woven textiles, as well as eyed sewing needles and other fine instruments for the making of tailored clothing (Hoffecker, 2002, p. 161, 107).

Much of this activity was driven by the need to do a lot in a short time:

 

In such [non-tropical] areas, one or two seasonally abundant resources may be relied on to produce the critical storable surplus for the lean seasons. This would require short periods of intensive harvest and precise scheduling during those times of the year when these resources were available. In such ‘time-stressed environments’, time was at a premium and hunter-gatherer societies responded by developing time-saving devices: by budgeting their time and by preparing in advance more sophisticated, but also more complicated tools designed for the specific tasks involved. The development of capture facilities, such as pits, traps, weirs, and nets can be also seen as time-saving devices. Another technological requirement for effective exploitation of seasonal resources consists of storage. […] These technological developments, combined with the development of the microlithic industry, could be called, with some justification, the original industrial revolution. (Zvelebil, 2009, p. 170)

 

Did these new cognitive demands have an evolutionary impact? Did they select for certain mental capacities over others? Piffer (2013) has addressed these questions by seeing how hunter-gatherers differ from farming peoples in alleles at COMT, a gene linked to executive function, working memory, and intelligence:

Ethnic groups whose economy is based on farming have higher frequencies of the Met allele (symbol: A), whereas societies based on a hunter-gatherer economy have very low frequencies of the Met allele and a disproportionate predominance of the Val allele. Moreover, the frequency of the Met allele was positively correlated to the populations’ IQ (r = 0.57).

Northern hunting peoples, however, differ from other hunter-gatherers and resemble more advanced farming populations:

[…] hunter-gatherers living at high latitudes (Inuit) show high frequencies of the Met allele, possibly due to the higher pressure on technological skills and planning abilities posed by the adverse climatic conditions near the North Pole.

 

Conclusion

Modern humans arose in Africa, and founded the first civilizations in the Middle East. These two milestones are separated by the development of a new mental toolkit, i.e., an improved ability to imagine how resources can be used collectively not only in the present but also over long periods of time in the future. Surely, then, this mental toolkit must have arisen in the same geographic area. Wouldn’t that be the simplest answer? 

Sometimes the simplest answer is not the right one. Evolution can appear unnecessarily complicated at times, and this is a fine example. Although the new mental toolkit was initially an adaptation to harsh semi-Arctic conditions, it would later prove useful in warmer climes. We see this in an apparent series of demographic expansions out of the northern tier of Eurasia, beginning as early as 15,000 years ago, as indicated by the existence of the Eurasiatic language macrofamily and the more hypothetical Borean macrofamily. Today, most of the human gene pool has its origins in people who once roamed the northern wastes of Eurasia.

References 

Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.

Piffer, D. (2013). Correlation of the COMT Val158Met polymorphism with latitude and a hunter-gather lifestyle suggests culture–gene coevolution and selective pressure on cognition genes due to climate, Anthropological Science, 121, 161-171.

https://lesacreduprintemps19.files.wordpress.com/2014/01/correlation-of-the-comt-val158met-polymorphism-with-latitude-and-a-hunter-gather-lifestyle-suggests-culturee28093gene-coevolution-and-selective-pressure-on-cognition-genes-due-to-climate.pdf

Zvelebil, M. (2009). Hunters in Transition: Mesolithic Societies of Temperate Eurasia and Their Transition to Farming, Cambridge University Press. 

A detour through Europe?

The lithic technology of southwestern France (c. 22,000-17,000 BP) strangely resembles that of the first paleo-Amerindians (c. 12,000). Some people speculate that early Europeans reached North America by crossing the Atlantic. The truth is even more incredible. Early Europeans spread eastward and became the ancestors not only of the Amerindians but also of East Asians. (source)

The recent study by Beleza et al. (2012) has elicited comment on two findings:
 

1. European skin turned white long after modern humans had entered Europe (c. 40,000 BP). Moreover, it whitened relatively fast—between 19,000 and 11,000 years ago. Such a narrow timeframe implies some form of selection, and not just relaxation of selection for darker skin. 

2. The new skin-color alleles did not come from the Neanderthals. This point may have broader repercussions because some have argued that the rapidity of evolution among modern humans required “cherry picking” of useful alleles from Neanderthals and other archaic hominins.

But another finding deserves comment. This is the discovery that an earlier (though minor) lightening of skin color had occurred shortly after the entry of modern humans into Europe:

[…] the initial stages of European skin lightening occurred in a proto-Eurasian population, about 30,000 years ago, after the out-of-Africa migration ~60,000-70,000 years ago […] and slightly more recently than the earliest archaeological evidences for the dispersal of anatomically modern humans in Europe, around 40,000 years ago (Beleza et al., 2012).

It’s widely accepted that the ancestors of Europeans and East Asians parted company long after modern humans had begun spreading out of Africa. It’s usually assumed, however, that this splitting took place somewhere in the Middle East or Central Asia. If we are to believe Beleza et al (2012), it must have happened after the entry of modern humans into Europe.

So the first Europeans were also the first East Asians. Cro-Magnon Man wasn’t just a proto-European. He was also a proto-Eurasian.

From Africa to East Asia … by way of Europe?

A straight line isn’t always the easiest route from point A to point B. In any case, modern humans weren’t going anywhere in particular when they began spreading out of Africa. They were seeking new lands and following the path of least resistance.

Let’s suppose you’re a band of hunter-gatherers in the Levant circa 50,000 BP. What new territories would tempt you? The Iranian Plateau and, beyond it, the arid steppes of Central Asia? No, that doesn’t seem very tempting.

You would look to lands farther north and west along the Mediterranean. Those lands are similar in climate, vegetation, and wildlife. You can continue using the same life skills, since the means of subsistence are almost the same.

As your descendants grow in numbers and spread farther out, they will eventually bump up against an ecological zone that differs in climate, vegetation, and wildlife. At that point, they’ll have to stop their advance and begin a slow process of adaptation within transitional environments on the edge of this zone. Once they’ve sufficiently adapted, they will break out from this “beachhead.” And begin a new wave of advance.

This is what happened when modern humans spread north from the Mediterranean and into more boreal environments with wider seasonal variations. Finally, they encountered the Eurasian steppe-tundra—a vast open plain of grassland stretching from southwestern France to Manchuria. Living in that environment would require a whole suite of new adaptations. The men would have to become much more mobile in order to hunt the herds of wandering herbivores. The women would have to abandon food gathering and take on new tasks like shelter building and garment making. So where do you think those adaptations were developed?

In southwestern France. This “beachhead” was the most southerly and resource-rich portion of the Eurasian steppe-tundra (Mellars, 1985). Sheltered valleys dissected the steppe and offered trees and other non-arctic vegetation, particularly on south-facing slopes (Blades, 1999b). In this protected environment, hunter-gatherers could live off salmon, local game, wild fruits, grains, and tubers while hunting reindeer herds that passed through in the fall and winter (Blades, 1999a; Blades, 1999b; Mellars, 1985). As the climate improved from 30,000 to 27,000 BP, closed forests became established, the herds moved further afield, and reindeer hunting was all but abandoned at valley sites (Blades, 1999b). The men had to move out of the valleys and onto the surrounding tundra tablelands. They now had to make further adaptations: more efficient use of raw materials (wood for fire and shelter, lithic materials); long-distance travel to procure them; and development of extensive social networks (Goebel, 1999; Hahn, 1987).

Sometime after 28,000 BP, they broke out from the beachhead and colonized the tundra plains in their entirety. This breakout may correspond to a demographic expansion (23,000-21,000 BP) of a genetic lineage that occurs most often among the Basques of northern Spain and southwestern France (Richards et al., 1996; Richards et al., 2000). Relatively few people were involved, as indicated by the very low variability of the northern European gene pool (Reich et al., 2001). Presumably, there were many semi-isolated groups, each one tinkering with its own mix of cultural adaptations until one of them got it right and colonized the Eurasian steppe-tundra.

After the breakout, nothing could stop them from spreading east throughout the Eurasian steppe-tundra … all the way to the Pacific Ocean, and from there to Beringia and North America. They would in time become the ancestors of most people living today, not only Europeans but also East Asians and Amerindians.

For this, we have several lines of evidence:

- a Y-chromosome study has found that all North Eurasian peoples descend from a common ancestral population dated to about 15,000 BP (Stepanov & Puzyrev, 2000; see also Armour et al., 1996; Santos et al., 1999; Zerjal et al., 1997).

- the language families of northern Eurasia, particularly Uralic and Yukaghir and more generally Uralic-Yukaghir, Eskimo-Aleut, Chukotko-Kamchatkan and Altaic, share deep structural affinities that point to a common origin and not simply to word borrowing (Cavalli-Sforza, 1994, pp. 97-99; Fortescue, 1998; Rogers, 1986).

- archeological evidence (characteristic lithic technology, grave goods with red ocher, and sites with small shallow basins) also suggests a common cultural tradition throughout Europe and Siberia 20,000 to 15,000 years ago (Goebel, 1999; Haynes, 1980; Haynes, 1982).

- dental and cranial remains from Mal’ta (23,000-20,000 BP) in southern Siberia indicate strong affinities with Upper Paleolithic Europeans (Alexeyev & Gokhman, 1994; Goebel, 1999).

Finally, the lithic technology of southwestern France (c. 22,000-17,000 BP), referred to as “Solutrean”, strangely resembles that of the first paleo-Amerindians (c. 15,000-12,000). Solutrean and Clovis points share common characteristics. Both are thin and bifacial, and both share the intentional use of the outre passé, or overshot flaking technique, which quickly reduces the thickness of a biface without reducing the width.

This similarity has led to the “Solutrean hypothesis”— the idea that early Europeans reached North America by crossing the Atlantic. Again, the easiest route between two points isn’t always a straight line. For the proto-Eurasians of southwestern France, the road to North America ran east ... over the unbroken grasslands of the Eurasian steppe-tundra.

References

Alexeyev, V.P., & Gokhman, I.I. (1994). Skeletal remains of infants from a burial on the Mal'ta Upper Paleolithic site. Homo, 45, 119‑126.

Armour, J.A.L., Anttinen, T., May, C.A., Vega, E.E., Sajantila, A., Kidd, J.R., Kidd, K.K., Bertranpetit, J., Paabo, S., & Jeffreys, A.J. (1996). Minisatellite diversity supports a recent African origin for modern humans. Nature Genetics, 13, 154‑160.

Beleza, S., A. Múrias dos Santos, B. McEvoy, I. Alves, C. Martinho, E. Cameron, M.D. Shriver, E.J. Parra, & J. Rocha. (2012). The timing of pigmentation lightening in Europeans, Molecular Biology and Evolution, 20, online

Blades, B.S. (1999a). Aurignacian settlement patterns in the Vézère valley, Current Anthopology, 40, 712-719.

Blades, B.S. (1999b). Aurignacian lithic economy and early modern human mobility: new perspectives from classic sites in the Vézère valley of France, Journal of Human Evolution, 37, 91-120.

Cavalli-Sforza, L.L., Menozzi, P. & Piazza, A. (1994). The History and Geography of Human Genes. Princeton: Princeton University Press.

Fortescue, M.D. (1998). Language Relations across Bering Strait. Reappraising the Archaeological and Linguistic Evidence. Cassell: London.

Goebel, T. (1999). Pleistocene human colonization of Siberia and peopling of the Americas: An ecological approach. Evolutionary Anthropology, 8, 208‑227.

Hahn, J. (1987). Aurignacian and Gravettian settlement patterns in Central Europe. In The Pleistocene Old World, O. Soffer (Ed.). New York: Plenum Press, pp. 251‑261.

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Haynes, C.V. (1980). The Clovis culture. Canadian Journal of Anthropology, 1, 115‑121.

Mellars, P.A. (1985). The ecological basis of social complexity in the Upper Paleolithic of Southwestern France. In Prehistoric Hunter‑Gatherers. The Emergence of Cultural Complexity, T.D. Price & J.A. Brown (Eds.). Orlando: Academic Press, pp. 271‑297.

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Richards, M., H. Côrte-Real, P. Forster, V. Macaulay, H. Wilkinson-Herbots, A. Demaine, S. Papiha, R. Hedges, H.-J. Bandelt, & B. Sykes. (1996). Paleolithic and Neolithic lineages in the European mitochondrial gene pool, American Journal of Human Genetics, 59, 185-203.

Richards, M., V. Macaulay, E. Hickey, E. Vega, B. Sykes, et al. (2000). Tracing European founder lineages in the Near Eastern mtDNA pool, American Journal of Human Genetics, 67, 1251-1276.

Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia. Canadian Journal of Anthropology, 5, 11‑22.

Santos, F.R., Pandya, A., Tyler‑Smith, C., Pena, S.D.J., Schanfield, M., Leonard, W.R., Osipova, L., Crawford, M.H., & Mitchell, R.J. (1999). The Central Siberian origin for Native American Y chromosomes. American Journal of Human Genetics, 64, 619‑628.

Stepanov, V.A., & Puzyrev, V.P. (2000). Evolution of Y‑chromosome haplotypes in populations of North Eurasia. American Journal of Human Genetics, 67, 220.

Zerjal, T., Dashnyam, B., Pandya, A., Kayser, M., Roewer, L., Santos, F.R., Scheifenhövel, W., Fretwell, N., Jobling, M.A., Harihara, S., Shimizu, K., Semjidmaa, D., Sajantila, A., Salo, P., Crawford, M.H., Ginter, E.K., Evgrafov, O.V., & Tyler‑Smith, C. (1997). Genetic relationships of Asians and Northern Europeans, revealed by Y‑chromosomal DNA analysis. American Journal of Human Genetics, 60, 1174‑1183.