Recent cognitive evolution in Europe: a new study of ancient DNA

 

Polygenic scores for alleles associated with educational attainment - Europeans of different time periods (Kuijpers et al. 2022)

 

According to a new study of ancient European DNA, cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now.

 

 

In my last post, I mentioned an ancient DNA study of 99 genomes from sites across Europe and Central Asia. It showed an apparent increase in mean cognitive ability between 4,560 and 1,210 years ago, as measured by alleles associated with educational attainment (Woodley et al. 2017).

 

That finding has been partially replicated by a new study of 827 genomes from ancient European remains and 250 genomes from modern Europeans. It looks like cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now:

 

Interestingly, while the period between the Early Upper Paleolithic and the Neolithic is characterized by stagnation or slight decrease in PRS related to intelligence, the genetic data show a clear increase in the scores for educational attainment, intelligence, and fluid intelligence from the Neolithic onwards, while the traits related with unipolar depression tend to decrease from that era on. The most significant differences can be observed comparing the pre-Neolithic and Neolithic groups, as well as the post-Neolithic and modern groups, whereas the period between the Neolithic and post-Neolithic shows a very constant distribution of PRS scores. (Kuijpers et al. 2022).

 

The authors define the time periods as follows:

 

Early Upper Paleolithic era – before 28,000 years BC

Late Upper Paleolithic era – 28,000 to 11,000 BC

Mesolithic - 11,000 to 5500 BC

Neolithic - 8,500 to 3900 BC

Post-Neolithic - 5000 BC and more recent ages (no end date given)

Modern – circa 1950 AD

 

The Mesolithic, the Neolithic, and the Post-Neolithic overlap a lot with each other. This is because their boundaries are defined by cultural changes that came to different parts of Europe at different times. The Neolithic began when hunting and gathering gave way to farming, which came later to northern Europe. Similarly, the post-Neolithic began with the advent of metallurgy, which likewise came later to northern Europe.

 

Such overlap is problematic for three reasons:

 

·         In some cases, there is uncertainty as to whether the ancient DNA came from the remains of hunter-gatherers or those of farmers.

·         “Hunter-gatherer” is not a homogeneous category. It includes not only small nomadic groups but also the hunter-fisher-gatherers of the Baltic and North Sea, who attained a degree of sedentism, population growth, and social complexity that we normally associate with farmers (Price 1991).

·         The Post-Neolithic is too long to be meaningful. It covers all of recorded history, and then some.

 

The study’s authors could have divided the Post-Neolithic into smaller time periods to give us a better look at changes during historical times. In particular, did cognitive evolution regress during Classical Antiquity? That was the preliminary finding of a team led by Michael Woodley of Menie (2019) in a study of ancient DNA from Greece. They found that mean cognitive ability increased from the Neolithic to the Mycenaean period and then decreased sometime between the latter and the present day. That study was never published, perhaps because the geographic area and the time periods were too small to provide robust results.

 

To get more robust results, we could look at ancient DNA from the entire Greco-Roman world, perhaps divided into three time periods: 5000 to 1000 BC; 1000 to 0 BC; and 0 to 500 AD. Was there a large increase in mean cognitive ability followed by an equally large decrease? Or was there simply a long period of stagnant evolution?

 

In a previous post, I argued that the culture of Classical Antiquity, particularly in its later stages, caused cognitive evolution to regress (Frost 2022). There were several reasons:

 

·         A decline in fertility and family formation, particularly among the upper classes;

·         A corresponding increase in female hypergamy, often by freed slaves, which reduced the reproductive importance of upper-class women;

·         An increase in the foreign slave population, which disrupted cognitive evolution within the local population. Even if there had been demographic overflow from the upper classes, that overflow could not have replaced the lower classes, since those classes were being replaced from external sources.

 

We need a clearer picture. According to the current data, it looks like cognitive evolution simply stagnated during the Post-Neolithic, but I suspect that time period is so broadly defined that it conceals a regression during the centuries before the fifth century collapse and the centuries immediately after.

 

References

 

Frost, P. (2022). When did Europe pull ahead? Evo and Proud, May 16. http://evoandproud.blogspot.com/2022/05/when-did-europe-pull-ahead.html

 

Kuijpers, Y., J. Domínguez-Andrés, O.B. Bakker, M.K. Gupta, M. Grasshoff, C.J. Xu, Joosten LAB, J. Bertranpetit, M.G. Netea, and Y. Li. (2022). Evolutionary Trajectories of Complex Traits in European Populations of Modern Humans. Frontiers in Genetics 13: 833190. https://doi.org/10.3389/fgene.2022.833190

 

Price, T.D. (1991). The Mesolithic of Northern Europe. Annual Review of Anthropology, 20, 211-233. Price, T. D. (1983). The European Mesolithic. American Antiquity 48(4), 761–778. https://doi.org/10.2307/279775  

 

Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280. https://doi.org/10.1017/thg.2017.37

 

Woodley of Menie, M.A., J. Delhez, M. Peñaherrera-Aguirre, and E.O.W. Kirkegaard. (2019). Cognitive archeogenetics of ancient and modern Greeks. London Conference on Intelligence 

https://www.youtube.com/watch?v=UES_tpDxz9A  

British hipsters

Why have British women become broader-hipped over the past three thousand years? (Wikicommons: Niek Sprakel)



British women have become broader-hipped over the past three thousand years or so. That's the conclusion of a recent study of alleles that influence female hip circumference, using data from the UKBiobank. 

Audrey Arner and her colleagues at Penn State identified 148 SNPs associated with female hip circumference and 49 SNPs associated with first child birth weight. Nine of them influence both women's hip circumference and first child birth weight. The SNPs associated with female hip circumference seemed to influence first child birth weight but not vice versa. There also seems to have been selection over approximately the last three thousand years for women with broader hips.

The baby's head is the biggest challenge during childbirth:

Human birthing is difficult owing to a tradeoff between large neonatal brain size and maternal pelvic dimensions, which are constrained by aspects of bipedal biomechanics. The net effect is that human neonatal head size closely matches maternal pelvic dimensions, unlike in our closest living relatives, the great apes, whose pelvic dimensions are larger than neonatal head sizes. (Franciscus 2009)

Have female hips become broader over the past three thousand years because the birth canal has had to accommodate babies with larger brains? That hypothesis would be consistent with an analysis of ancient DNA by Michael Woodley of Menie and others, who showed that alleles for educational attainment gradually increased in frequency between 4,560 and 1,210 years ago in Europeans and Central Asians. That increase may have been due to gene-culture coevolution: as societies grew larger and more complex, the average person had to perform mental tasks that likewise became larger in number and more complex. Such an environment would have favored the survival and reproduction of individuals with higher cognitive ability. Mean IQ thus rose over time, as did cranial capacity.

On the other hand, Henneberg (1988) showed that cranial capacity steadily shrank from the Mesolithic to modern times, becoming 9.9% smaller in men and 17.4% smaller in women. His conclusion was based on a large sample: 9,500 male skulls and 3,300 female skulls.

So we have a contradiction. Perhaps cranial capacity didn't really shrink from the Mesolithic to modern times. Perhaps smaller skulls are more likely to decompose faster. The skulls we unearth would therefore be a biased sample, and this bias toward preservation of larger skulls would gradually increase for skulls that have been in the ground longer.

The problem of "preservation bias" has already been noted with respect to female and infant remains:

There are nearly always more males than females in skeletal collections from archeological sites [...]. This has been explained in part by the comparatively rapid disintegration of lightly built female skeletons.

[...] The burial records show that most of the people buried in the Purisima cemetery were either infants, children, or elderly adults. The skeletal remains excavated from the cemetery, in contrast, are predominately those of young adults. The underrepresentation of young children in the skeletal collection is most likely a result of the comparatively rapid disintegration of their incompletely calcified bones.

[...] If, on the other hand, infants or elderly people are more common in a skeletal collection from a recent cemetery than they are in an ancient one, much less can be inferred about differences in the original age structure of the two burial populations. Such a difference would be expected due to differential preservation, even if the age structures of the two burial populations were identical. (Walker et al. 1988)

The same preservation bias might cause an overrepresentation of larger skulls among older remains.


References

Arner, A., H. Reyes-Centeno, G. Perry, and M. Grabowski. (2020). Pleiotropic effects on the recent evolution of human hip circumference and infant body size. The 89th Annual Meeting of the American Association of Physical Anthropologists (2020), April 17
https://meeting.physanth.org/program/2020/session26/arner-2020-pleiotropic-effects-on-the-recent-evolution-of-human-hip-circumference-and-infant-body-size.html  

Franciscus, R.G. (2009). When did the modern human pattern of childbirth arise? New insights from an old Neandertal pelvis. Proceedings of the National Academy of Sciences 106(23): 9125-9126.
https://www.pnas.org/content/106/23/9125.short  

Henneberg, M. (1988). Decrease of human skull size in the Holocene. Human Biology 60: 395-405.
https://www.jstor.org/stable/41464021  

Walker, P.L., J.R. Johnson, and P.M. Lambert. (1988). Age and sex biases in the preservation of human skeletal remains. American Journal of Physical Anthropology 76: 183-188.
https://onlinelibrary.wiley.com/doi/abs/10.1002/ajpa.1330760206

Woodley of Menie, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: Comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280.
https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/holocene-selection-for-variants-associated-with-general-cognitive-ability-comparing-ancient-and-modern-genomes/BF2A35F0D4F565757875287E59A1F534 

The ghosts of West Africa

Bushmen in the Kalahari (Wikicommons, Andy Maano). When recorded history began, in Sumer and Egypt, black Africans were absent from most of Africa, even from most of West Africa. The lands south of the Sahara were largely home to various hunter-gatherers who were small, almost childlike in build, and light reddish-brown in color. 

Most Americans think of native Africans as black and of white Africans as recent intruders; and when they think of Africa's racial history they think of European colonialism and slave trading. But very different types of peoples occupied much of Africa until as recently as a few thousand years ago.

When Jared Diamond penned those words, analysis of ancient DNA was years away. Even when it began, there was a feeling that such analysis would always be impractical in Africa or anywhere else in the tropics. The climate is too warm for that stuff to last thousands upon thousands of years.

Apparently not. DNA has been retrieved from the remains of four individuals at a site in Cameroon, two of them going back 8,000 years and the other two 3,000 years. The main finding? The individuals were most similar to Pygmies, who still exist as isolated groups of hunter-gatherers in the Congo basin. There was no genetic similarity to the Bantu peoples who now predominate throughout central, eastern, and southern Africa (Lipson et al. 2020).

This finding is no surprise. Linguistic evidence has shown that the Bantu are all descended from a group of farming peoples who, some two to three thousand years ago, began to expand eastward and southward from what is now the Cameroon-Nigeria border. 

More intriguing is the discovery of admixture from an extinct West African people. These were hunter-gatherers who shared common ancestry with the Pygmies of central Africa and the Khoisans of southern Africa; however, they had intermixed much more with an archaic hominin that had diverged from ancestral modern humans at about the same time as the Neanderthals:

The West African clade is distinguished by admixture from a deep source that can be modelled as a combination of modern human and archaic ancestry. The modern human component diverges at almost the same point as Central and southern African hunter-gatherers and is tentatively related to the deep source that contributes ancestry to the Mota individual, and the archaic component diverges close to the split between Neanderthals and modern humans (Lipson et al. 2020)

This suggests that the Bantu expansion was the second leg of an earlier expansion of farming peoples who had first replaced the hunter-gatherers of West Africa. This is in line with the thinking of George Murdock, an American anthropologist who argued that black Africans originated with the spread of agriculture from the Niger's headwaters, near the Mali-Guinea border. This region was the cradle of the Sudanic food complex: sorghum, pearl millet, cow pea, and other crops.

Murdock’s scenario is supported by linguistic evidence. Speakers of proto-Niger-Congo broke up around 10,000 years ago, and the oldest group appears to be proto-Mande speakers, whose descendants inhabit the Niger's headwaters (Blench 1984, pp. 128-129; Ehret 1984; Murdock 1959, pp. 44, 64-68). Farming itself seems to have begun later. According to Harris (1976, p. 352), “the problem of dating must be left in abeyance, but it is clear that some form of seed-crop cultivation was underway in the interior at least by the second millennium B.C.”

It looks like a stable population of hunter-gatherers took shape on the Niger’s headwaters around 10,000 years ago. They gradually became proto-agricultural, i.e., more sedentary and better able to manage their food sources. By 4,000 years ago, they had become true farmers and were entering a phase of sustained demographic expansion that would see them colonize the banks of the Niger farther and farther downstream until they reached the rain forest in southern Nigeria. As they adapted to this new environment, they reached a modus vivendi with the Pygmy inhabitants, at first as tenants and then as de facto landowners who took over more and more of the land. Meanwhile, the Pygmies were pushed back farther and farther into the forest until they were no more.

In sum, farming can support a much larger population, and it was this demographic advantage that enabled farming peoples to replace hunter-gatherers, first in West Africa and eventually throughout almost all of sub-Saharan Africa.


Memories of the first West Africans

Those hunter-gatherers are remembered in the traditions of West Africa: 

Pygmies may have been the first inhabitants of Côte d'Ivoire. In their oral tradition, most of the present-day peoples, in particular the Dan-Yacouba, recount that their ancestors, on arriving in the country, found "little red men" whom they pushed back into the forest. Others speak of "little brown men", who had supernatural powers and to whom presents were given to win them over. (Mantongouine 2012)

According to some authors like Allou and Gonnin, the presence of these mysterious beings appears in the oral traditions. They are presented as short beings about 1m 44 to 1m 55 according to J.N. Loucou, with reddish skin, abundant hair, and feet pointing backward. They appear in almost all of the regions of prehistoric Côte d’Ivoire in the sense that almost all of the oral traditions of Côte d’Ivoire’s ethnic groups affirm that they found pygmies in the area before they became established. (Afri 2013; see also Gonnin and Allou 2006; Loucou 1984, p. 18)

Everywhere, but mainly in the countries from which the Pygmies have long disappeared, the Blacks who are considered to be the oldest occupants of the land say that it does not really belong to them and that, when their distant ancestors, coming from the East, established themselves, they found it in the possession of little men with reddish complexions and large heads who were the real natives and who, in exchange for fulfilment of certain agreements, permitted the Negroes who first arrived on a piece of land to enjoy its use and cultivate it. Eventually, those little men disappeared, but the memory of them has persisted. (Delafosse 1922, p. 14)

The Mano of Liberia say that the forested area used to contain only “talking chimpanzees.” These small creatures, called Lam, inhabited the area when the Mano first came. A Lam and his family would live in a hole in the ground (Riddell 1970, p. 27).


Year-round farming, polygyny. and increased stature and robustness

In addition to their means of subsistence, this expanding population of farmers differed from the hunter-gatherers in another way: a much higher rate of polygyny. Farming, especially year-round farming, makes women more self-reliant in feeding themselves and their children, thus cutting the costs, for a man, of having a second wife (van den Berghe 1979, p. 65). The result is a high polygyny rate: 20-50% of all marriages in sub-Saharan farming societies (Bourguignon and Greenbaum 1973, p. 51; Goody 1973; Pebley and Mbugua 1989; Welch and Glick 1981; White 1988).

If some men have more wives, others have to do without. In general, men must compete more keenly with each other for access to women. When such rivalry intensifies in nonhuman species, there is selection for larger, stronger, and more muscular males. This may explain the physical robustness of polygynous farming peoples in sub-Saharan Africa.

This point was studied by Butovskaya et al. (2015) in their study of two East African peoples: the polygynous Datoga and the monogamous Hadza. Datoga men were larger and more robust than Hadza men. They also scored higher on measures of physical aggression, verbal aggression, anger, and hostility. In fact, the two groups differed fundamentally in their attitudes toward aggression:

There is a negative attitude toward aggression among the Hadza but not among the Datoga. In situations of potential aggression, the Hadza prefer to leave. In contrast, aggression is an instrument of social control — both within the family and in outgroup relations — in Datoga society. Datoga men are trained to compete with each other and to act aggressively in particular circumstances.  (Butovskaya et al. 2015).

The two groups also differed at the androgen receptor gene, with the polygynous Datoga more often having an allele that correlated in men with aggressiveness and number of children fathered. Thus, through a process of gene-culture coevolution, a highly polygynous culture has produced a different sort of man, both mentally and physically.

There are other explanations for the diminutive and less robust appearance of African hunter-gatherers. O'Dea (1994) has argued that Pygmies are smaller and less robust because they are less exposed to sunlight in the rain forest and thus less able to synthesize vitamin D and maintain a large and strong skeleton. But how would this theory explain the small, gracile appearance of the Khoisan hunter-gatherers of the Kalahari, who live in an open environment with high solar radiation?


Darker skin

The polygyny rate correlates with darkness of skin, even after you control for latitude (Manning et al. 2004). This is particularly so in sub-Saharan Africa, where highly polygynous farming peoples are noticeable darker than the largely monogamous Pygmy and Khoisan hunter-gatherers. The reason may be a widespread mental association between gender and skin color. Because women are naturally lighter-skinned than men, traditional cultures tend to associate light skin with femininity and dark skin with masculinity (van den Berghe and Frost 1986). There is thus a selective compromise between natural selection for darker skin as a protection against solar radiation and sexual selection for lighter skin as a criterion of femininity (or darker skin as a criterion of masculinity). 

Because unmated women of any kind are scarce in a polygynous society, there is weaker sexual selection for women with lighter skin. This may be why farming peoples are noticeably darker-skinned in sub-Saharan Africa (Frost 2008).


Archaic admixture in West Africa

The ancient DNA study is also consistent with evidence that a partially archaic population used to live in West Africa. One piece of evidence is a skull from a Nigerian site (Iwo Eleru), which is only about 16,300 years old and yet is intermediate in shape between the skulls of modern humans on the one hand and the skulls of Neanderthals and Homo erectus on the other (Harvati et al. 2011; Stojanowski 2014). Furthermore, genomic analysis shows an apparently higher level of Neanderthal ancestry in the Yoruba of Nigeria than in the Luhya of Kenya. This admixture seems to come from a Neanderthal-like population that once lived in West Africa (Hawks 2012).


Conclusion

In the fifteenth century, Europeans discovered a continent whose inhabitants would have looked quite different a millennium earlier. Two tenth-century Arab geographers reported that "in the outer reaches of the land of the Zanj there are cool highlands in which live white Zanj" (Lewis 1990, p. 121, n. 3). The Zanj are the dark-skinned peoples of east Africa and the “white Zanj” were probably the Khoisan hunter-gatherers who once inhabited the inland plateau of southern Africa.

If we could rewind history, we would see true black Africans retreating progressively to West Africa and then to the area of the Niger’s headwaters. This leads us to a strange conclusion. When recorded history began, in Sumer and Egypt, black Africans were absent from most of Africa, even from most of West Africa. Perhaps they didn’t yet exist anywhere. The lands south of the Sahara were largely home to various hunter-gatherers who were small, almost childlike in build, and light reddish-brown in color. 


References

Afri, A. (2013). Existait-il des peuples en Côte d’Ivoire avant le XVIIIème siècle ?
http://anicetafri.over-blog.com/existait-il-des-peuples-en-cote-d’ivoire-avant-le-xviiième-siÈcle

Blench, R. (1995). Recent developments in African language classification and their implications for prehistory. In T. Shaw, P. Sinclair, B. Andah, and A. Okpoko (Eds.) The Archaeology of Africa (pp. 126-138). London: Routledge.

Butovskaya M.L., O.E. Lazebny, V.A. Vasilyev, D.A. Dronova, D.V. Karelin, A.Z.P. Mabulla, et al. (2015). Androgen receptor gene polymorphism, aggression, and reproduction in Tanzanian foragers and pastoralists. PLoS ONE 10(8): e0136208.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4546275/ 

Delafosse, M. (1922). Les Noirs de l’Afrique. Paris: Collection Payot. 
https://www.herodote.net/Textes/delafosse_noirs_afrique.pdf

Diamond, J. (1994). How Africa Became Black. Discover, February 1
https://www.discovermagazine.com/planet-earth/how-africa-became-black

Ehret, C. (1984). Historical/linguistic evidence for early African food production. In J.D. Clark and S.A. Brandt (Eds.) From Hunters to Farmers: The Causes and Consequences of Food Production in Africa (pp. 26-35). Berkeley: University of California Press.

Frost, P. (2008). Origins of black Africans, Evo and Proud, February 10
http://evoandproud.blogspot.com/2008/02/origins-of-black-africans.html

Gonnin, G. and R.K. Allou. (2006). Côte-d’Ivoire : les premiers habitants. Abidjan: Les éditions du CERAP.

Goody, J. (1973). Polygyny, Economy and the Role of Women, in J. Goody (Ed.) The Character of Kinship, Cambridge: Cambridge University Press, pp. 175-190.

Harris, D.R. (1976). Traditional systems of plant food production and the origins of agriculture in West Africa. In J.R. Harlan, J.M.J. De Wet, and A.B.L. Stemler. (ed.) Origins of African Plant Domestication, (pp. 311-356), The Hague: Moulton.
https://books.google.ca/books?id=tGOtFegfro4C&lr=&hl=fr&source=gbs_navlinks_s

Harvati, K., C. Stringer, R. Grün, M. Aubert, P. Allsworth-Jones, C.A. Folorunso. (2011). The Later Stone Age Calvaria from Iwo Eleru, Nigeria: Morphology and Chronology. PLoS ONE 6(9): e24024. doi:10.1371/journal.pone.0024024
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0024024  

Hawks, J. (2012). Which population in the 1000 Genomes Project samples has the most Neandertal similarity? John Hawks Weblog, February 8
http://johnhawks.net/weblog/reviews/neandertals/neandertal_dna/1000-genomes-introgression-among-populations-2012.html  

Lewis, B. (1990). Race and Slavery in the Middle East. An Historical Enquiry. New York: Oxford University Press.

Lipson, M., I. Ribot, S. Mallick, et al. (2020). Ancient West African foragers in the context of African population history. Nature 577: 665-670.
https://reich.hms.harvard.edu/sites/reich.hms.harvard.edu/files/inline-files/Shum_Laka_published_online_0.pdf

Loucou, J-N. (1984). Histoire de la Côte-d’Ivoire. Tome 1 : La formation des peuples. Abidjan: Centre d’édition et de diffusion africaine (CEDA).

Manning, J.T., P.E. Bundred, and F.M. Mather. (2004). Second to fourth digit ratio, sexual selection, and skin colour. Evolution and Human Behavior 25(1): 38-50.
https://www.sciencedirect.com/science/article/abs/pii/S1090513803000825

Mantongouine. (2012). L'histoire de la Côte d'ivoire 
http://mantongouine.free.fr/index.php?option=com_content&view=article&id=66:lhistoire-de-la-cote-divoire&catid=34:description

Murdock, G.P. (1959). Africa. Its Peoples and Their Culture History. New York: McGraw-Hill.

O'Dea, J.D. (1994). Possible contribution of low ultraviolet light under the rain-forest canopy to the small stature of Pygmies and Negritos. Homo 44(3): 284-7.

Pebley, A. R., and Mbugua, W. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (Ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.

Riddell, J.C. (1970). Labor Migration and Rural Agriculture among the Gbannah Mano of Liberia. Dissertation, Department of Anthropology, University of Oregon.
https://scholarsbank.uoregon.edu/xmlui/bitstream/handle/1794/22554/Riddell_Labor%20Migration%20and%20Rural%20Agriculture.pdf?sequence=1&isAllowed=y

Stojanowski, C.M. (2014). Iwo Eleru's place among Late Pleistocene and Early Holocene populations of North and East Africa. Journal of Human Evolution 75: 80-89.
http://www.sciencedirect.com/science/article/pii/S0047248414000876

van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.

van den Berghe, P.L., and P. Frost. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies 9(1): 87-113.
https://www.tandfonline.com/doi/abs/10.1080/01419870.1986.9993516

Welch, C.E., and Glick, P.C. (1981). The incidence of polygamy in contemporary Africa: A research note. Journal of Marriage and the Family 43:191-193.

White, D. R. (1988). Rethinking polygyny. Co-wives, codes, and cultural systems. Current Anthropology 29: 529-572.

Classical antiquity was a low point of human intelligence

Aristotle discussed adaptation by natural selection long before Darwin, yet despite his fame this theory remained ignored throughout antiquity. (Wikicommons)



Gabriel Andrade and Maria Campo Redondo have come out with a paper on the ancient Greeks and how they saw differences between human groups:

Critics of Rushton and Jensen, and of the very category of race, claim that race is a social construct that only came up in the 16th century, as a result of overseas voyages and the Atlantic slave trade. The goal of this article is to refute that particular claim, by documenting how, long before the 16th century, in classical antiquity race was already a meaningful concept, and how some Greek authors even developed ideas that bear some resemblance to Rushton and Jensen's theory. The article documents how ancient Egyptians already had keen awareness of race differences amongst various populations. Likewise, the article documents passages from the Hippocratic and Aristotelian corpus, which attests that already in antiquity, there was a conception that climatic differences had an influence on intelligence, and that these differences eventually become enshrined in fixed biological traits. (Andrade and Redondo 2019)

The ancients knew about psychological differences between human groups but usually put them down to the direct action of the climate. This environmental explanation seemed disproved by black Africans, or "Ethiopians" as they were called, because they and their descendants remained just as dark-skinned at northern latitudes. But this example of heritability didn't lead to a theory of genetics. Instead, black skin was seen as an indelible stain, perhaps due to divine punishment of Ham (or Cham), the ancestor of the Egyptians and black Africans, for seeing the nakedness of his father Noah (Goldenberg 2003). This view appears in a homily by the third-century Christian writer Origen: 

But Pharao easily reduced the Egyptian people to bondage to himself, nor is it written that he did this by force. For the Egyptians are prone to a degenerate life and quickly sink to every slavery of the vices. Look at the origin of the race and you will discover that their father Cham, who had laughed at his father's nakedness, deserved a judgment of this kind, that his son Chanaan should be a servant to his brothers, in which case the condition of bondage would prove the wickedness of his conduct. Not without merit, therefore, does the discolored posterity imitate the ignobility of the race.   Homily on Genesis XVI (Origen 2010)

In general, human differences were attributed to direct action by the environment:

Greek authors to a large extent believed that acquired characteristics were inherited. For example, the text On Airs, Waters and Places considers the people of Trapezus, who had the custom of artificially elongating their children's heads. The author of this text believed that this particular practice would make elongated heads in the future generations, without parents having to artificially do the procedure: "Thus, at first, usage operated, so that this constitution was the result of force: but, in the course of time, it was formed naturally; so that usage had nothing to do with it... If, then, children with bald heads are born to parents with bald heads; and children with blue eyes to parents who have blue eyes; and if the children of parents having distorted eyes squint also for the most part; and if the same may be said of other forms of the body, what is to prevent it from happening that a child with a long head should be produced by a parent having a long head?". Aristotle had similar ideas: "Mutilated young are born of mutilated parents".

Why wasn’t natural selection understood?

Ironically, and long before Darwin, the Greek philosopher Empedocles (494-434 BC) came up with another explanation: adaptation through natural selection. Change initially occurs by accident. If the change is good, the changed life-form will survive and reproduce; if not, it will perish. Good changes are therefore kept and bad changes lost. Thus, all aspects of living matter look "as if they were made for the sake of something," but this is only illusion. There is no conscious "maker" of all things. 

This idea was summarized by Aristotle (384-322 BC):

So what hinders the different parts (of the body) from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident. And in like manner as to other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity; and whatsoever things were not thus constituted, perished and still perish. Physicae Auscultationes 2:8, 2 (Darwin 1936 [1888], p. 3)

Aristotle's fame, as well as Empedocles', ensured that this idea would be read and passed on for generations, and yet it failed to take root in the minds of classical antiquity. It fell on barren ground. Aristotle himself rejected it, saying that all things must be for an end. Only much later, and independently, would natural selection be rediscovered.

The difficulty was not in understanding that humans, like other animals, are adapted to their environment. That part was obvious. The difficulty was in understanding adaptation as an indirect process. People more easily understood direct processes: something changed some people, and that change was passed on to their descendants. Aristotle himself fell for that idea when he mused that mutilated young are born to mutilated parents. 

This was the mentality of classical antiquity, and indeed of many people today. Change implies the existence of a changer, just as creation implies the existence of a creator. Few people rose above that level of thinking.


Did most people in classical antiquity think like children?

A Swiss psychologist, Jean Piaget (1896-1980), studied children in his country and concluded that all individuals go through stages of mental development. Children go through a "pre-operational stage" when causality is understood only in terms of conscious intent, specifically animism, artificialism, and transductive reasoning:

Animism is the belief that inanimate objects are capable of actions and have lifelike qualities. An example could be a child believing that the sidewalk was mad and made them fall down, or that the stars twinkle in the sky because they are happy. Artificialism refers to the belief that environmental characteristics can be attributed to human actions or interventions. For example, a child might say that it is windy outside because someone is blowing very hard, or the clouds are white because someone painted them that color. Finally, precausal thinking is categorized by transductive reasoning. Transductive reasoning is when a child fails to understand the true relationships between cause and effect. Unlike deductive or inductive reasoning (general to specific, or specific to general), transductive reasoning refers to when a child reasons from specific to specific, drawing a relationship between two separate events that are otherwise unrelated. For example, if a child hears the dog bark and then a balloon popped, the child would conclude that because the dog barked, the balloon popped. (Wikipedia 2019)

Piaget correctly observed Swiss children in the mid-20th century. He incorrectly concluded that the mind develops at the same pace in all humans (Oesterdiekhoff 2012). Indeed, you need not go far back to reach a time when most individuals never developed beyond the pre-operational stage. Just go back to classical antiquity.

At that time, the smart fraction was relatively small. Most intellectuals seemed to be loners. There were no academic societies, no academic journals, and no indications that large numbers of scholars did, or could, interact with each other. This point is made in an article on Roman science:

According to Sarton, who is the foremost living historian of science, "Roman science at its best was but a pale imitation of the Greek." "The Romans," he continues, "were so afraid of disinterested research that they discouraged any investigation the utilitarian value of which was not obvious."

Reymond remarked in his "History of Science" that the Romans were never distinguished for any love or even interest in pure science or abstract thinking. Virtually the same conclusion was reached by Heiberg, and Fowler made the interesting observation that even their literature and their philosophy had a practical object.

[...] historians of the economic life of ancient Rome have shown that there was a surprising paucity of inventions. They were not only few in number, but they lacked originality and were unimportant. (Salant 1938)

The Roman Empire was organizationally strong but intellectually weak. It depended on a store of knowledge that had been laid up in earlier times, notably by the ancient Greeks. This was the prevailing opinion among Roman writers, an opinion today dismissed as nostalgia for a mythical golden age.


The evidence of ancient DNA

"Cognitive archaeology" is a new field that has been made possible by retrieval of DNA from human remains and by calculation of polygenic cognitive scores from this DNA (based on alleles associated with educational attainment).

To date, two studies have used these research tools to chart changes in mean intelligence. The first study used ancient DNA from Europe and central Asia and found that the polygenic cognitive score gradually increased between 4,560 and 1,210 years ago (Woodley of Menie et al 2017).

This finding has been nuanced by a second study, using a sample of ancient DNA that was much larger and only from ancient Greece. It found that mean intelligence was initially high in ancient Greece and then began to decline after the end of the Mycenaean period in 1100 BC (Woodley of Menie et al. 2019). It looks like intelligence was at first strongly advantageous as humans adapted to increasing social complexity: farming, sedentism, literacy … Then something made it much less advantageous.

Mean intelligence was therefore lower during Roman times in comparison both to Greece in earlier periods and to Europe in later periods. 


Conclusion

So was Aristotle the Gregor Mendel of natural selection? Not really. Aristotle was much more famous than Mendel, and his works were read over a much longer span of time. Furthermore, Mendel's findings had to wait only 35 years before getting their due recognition. Aristotle's thoughts on natural selection lay dormant for more than two millennia before their significance was pointed out to Charles Darwin.

Aristotle didn't suffer from being insufficiently known. He had a worse handicap, especially in this case: not enough people could understand his line of reasoning. He was a lone voice in the wilderness over the many centuries separating him from Darwin. By Darwin’s time, many more people could understand natural selection, both in absolute numbers and as a proportion of the population. Even before The Origin of Species Darwin had a large audience of thinking people who could answer his questions and comment on his ideas. Earlier thinkers were not so lucky.

In the final analysis, the people of classical antiquity failed to understand natural selection for the same reason they failed to understand economics. They preferred to imagine cause and effect in simple terms: a person or personified thing producing a big change over a short time, and not impersonal forces producing an accumulation of small changes over a long time. They thought like children.


References

Andrade, G. and M.C. Redondo. 2019. Rushton and Jensen's Work Has Parallels with Some Concepts of Race Awareness in Ancient Greece. Psych 1 (1): 391-402.
https://www.mdpi.com/2624-8611/1/1/28/htm

Aristotle. Physics
http://classics.mit.edu/Aristotle/physics.2.ii.html

Darwin, C. (1936) [1888]. The Origin of Species and The Descent of Man. reprint of 2nd ed., The Modern Library, New York: Random House.

Goldenberg, D.M. (2003). The Curse of Ham. Race and Slavery in Early Judaism, Christianity, and Islam. Princeton: Princeton University Press.

Oesterdiekhoff, G.W. (2012). Was pre-modern man a child? The quintessence of the psychometric and developmental approaches. Intelligence 40: 470-478.
http://www.iapsych.com/iqmr/fe/LinkedDocuments/oesterdiekhoff2012.pdf

Origen (2010). Homilies on Genesis and Exodus, transl. by R.E. Heine., Washington D.C.: Catholic University of America Press
https://books.google.ca/books?id=X_mSBavPcq4C&pg=PA214&source=gbs_toc_r&cad=2#v=onepage&q&f=false 

Salant, W. (1938). Science and Society in Ancient Rome. The Scientific Monthly 47(6): 525-535.
https://www.jstor.org/stable/16625?seq=1#page_scan_tab_contents 

Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Res Hum Genet 20: 271-280.
https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/holocene-selection-for-variants-associated-with-general-cognitive-ability-comparing-ancient-and-modern-genomes/BF2A35F0D4F565757875287E59A1F534

Woodley of Menie, M.A., J. Delhez, M. Peñaherrera-Aguirre, and E.O.W. Kirkegaard. (2019). Cognitive archeogenetics of ancient and modern Greeks. London Conference on Intelligence 
https://www.youtube.com/watch?v=UES_tpDxz9A 

Wikipedia (2019). Piaget's theory of cognitive development. https://en.wikipedia.org/wiki/Piaget%27s_theory_of_cognitive_development#Concrete_operational_stage

Why that stereotype and not the other?

Nubian Pyramids (Wikicommons - Petr Adam Dohnalek). In classical antiquity, contacts with black Africans were largely with Nubians, a people who already enjoyed a high level of material culture. 



A decade ago, Jason Malloy noted a curious fact: the ancient world did not see sub-Saharan Africans as less intelligent, despite the existence of other stereotypes, like macrophallia (Frost 2009, see comments; Thompson 1989). A stereotype of low intelligence is recorded in only two Greco-Roman texts, to the best of my knowledge. One is a reference by Ibn Khaldun (1332-1406 AD) to the Greek physician Galen (129-210 AD). The statement attributed to Galen does not appear in any of his works, at least not in those that have survived, and may be a false attribution.

We have seen that Negroes are in general characterized by levity, excitability, and great emotionalism. They are found to dance wherever they hear a melody. They are everywhere described as stupid. ... Al-Masfiüdi undertook to investigate the reason [for this]. However, he did no better than to report on the authority of ... al-Kindi and Jalinus [Galen] that the reason is a weakness of their brains which results in a weakness of their intellects. This is an inconclusive and unproven statement. ... The real reason is that ... joy and gladness are due to the expansion and diffusion of the animal spirit. Sadness is due to the opposite. (Hunwick 2005)

The other is the Christian parable of the Ethiopian woodcutter. The desert monk Arsenius (350-445 AD) recounted how an Ethiopian went out to gather wood. When the burden became too heavy, he put it down and continued to gather, but now his load was even heavier. So he put it down and gathered even more (Wallis Budge 1907). This parable is from late antiquity and may reflect the growing influx of black slaves into the Middle East during that period.

It seems, then, that low intelligence was not attributed to sub-Saharan Africans during classical antiquity, at least not often enough to become a stereotype. This stereotype would emerge later, during late antiquity and even more so during the Islamic period (Lewis 1990, pp. 46-47, 92-97).

I suspect there were two reasons:

- mean intelligence was probably lower in the Mediterranean world during classical antiquity, perhaps in the low 90s. This would be consistent with the apparently smaller size of its "smart fraction," in contrast not only to Western societies in later times but also to ancient Greece in earlier times (see July 13 post). In Roman society, intellectuals seem to have largely been isolated individuals. They did not come together to hold regular conferences or publish journals. While there were elementary schools, the ludus litterarius, there were no institutions of higher learning, only private tutors. The difference in mean intelligence with sub-Saharan Africa would have thus seemed smaller.

- contacts with dark-skinned Africans were initially most frequent with Nubians, who under Egyptian influence already enjoyed a high level of material culture and were thus already being selected for cognitive ability. Contacts with peoples farther south developed later, with development of the African slave trade. This trade seems to have slowly but steadily increased in volume during late antiquity and, subsequently, the Islamic period (Frost 2008).


Civilization and intelligence

So, beyond a certain point, does civilization actually select against intelligence? The short answer: yes, in some cases. 

Now for the long answer. First, increased intelligence comes at a cost:

The brain requires about 22 times as much energy to run as the equivalent in muscle tissue. The energy required to run every bodily process comes from the food we eat. Human brains are three times larger than our closest living relative, the chimpanzee, and use up to three times the energy, but the two species have the same metabolic rate. (Welsh 2011)

Because of that high energy cost, any excess intelligence is under strong negative selection and will decline noticeably—even over a few generations. Positive selection becomes confined to a minority of the population as a civilization develops and moves toward specialization of labor, i.e., the most difficult intellectual work is done by a minority while the majority performs menial tasks. 

Nonetheless, we have examples of advanced civilizations, notably in East Asia from ancient times and, later on, in Western Europe, where mean intelligence was and still is quite high. Those civilizations likewise had specialization of labor. So what made them different?

It seems to have been a process of internal demographic replacement that Gregory Clark described with respect to England and Ron Unz with respect to China. The mean intelligence of an entire population will steadily rise if two conditions are met:

1. Fertility is higher in higher social classes.

2. Class boundaries are sufficiently porous that the resulting demographic surplus of these classes can move downward and replace the lower classes.

Historically and cross-culturally, these two conditions were far from universal. In many societies, surplus members of the upper class preferred to remain unmarried and wait for a suitable high-status niche to open up. It was shameful to "lose caste" and enter a niche lower on the social ladder. Nor was fertility universally higher in higher social classes. In some cases, the rich and powerful had fewer children because they could count on other means of support for their old age. In other cases, they tended to congregate in towns and cities, where infant mortality was higher. Finally, greater sexual access to women often failed to translate into reproductive success because of infertility due to STDs or because of a culture of debauchery and indifference to married life.


Conclusion

With ancient DNA and polygenic cognitive scores, we can now understand history in a new light. Mean intelligence has risen and fallen during the time of recorded history, and not simply because of migrant influxes. The people may have been the same, and yet they really weren't:

Since it looks like there has been significant evolutionary change over historical time, we're going to have to rewrite every history book every written," said Gregory Cochran, a population geneticist at the University of Utah. "The distribution of genes influencing relevant psychological traits must have been different in Rome than it is today," he added. "The past is not just another country but an entirely different kind of people” (Wade 2006).

References

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World, 1st ed.; Princeton University Press: Princeton,

Frost, P. (2008). The beginnings of black slavery. Evo and Proud, January 25
http://evoandproud.blogspot.com/2008/01/beginnings-of-black-slavery.html

Frost, P. (2009). Skin color and Egyptian/Nubian encounters. Evo and Proud, April 23
http://evoandproud.blogspot.com/2009/04/skin-color-and-egyptiannubian.html

Hunwick, J.O. (2005). A region of the mind: Medieval Arab views of African geography and ethnography and their legacy. Sudanic Africa 16: 103-136
https://org.uib.no/smi/sa/16/16Hunwick.pdf

Lewis, B. (1990). Race and Slavery in the Middle East. Oxford University Press.

Thompson, L.A.  (1989). Romans and Blacks. Norman: University of Oklahoma Press.

Unz, R. (2013). How Social Darwinism made modern China. The American Conservative, March/April, 16-27.
https://www.theamericanconservative.com/articles/how-social-darwinism-made-modern-china-248/

Wade, N. (2006). The twists and turns of history, and of DNA. The New York Times, March 12, Week in Review 14

Wallis Budge, E.A. (1907). The Paradise of the Holy Fathers. London: Chatto and Windus.
https://books.google.ca/books?id=LX_sCgAAQBAJ&printsec=frontcover&hl=fr&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Welsh, J. (2011). Still up for debate. LiveScience, November 9
https://www.livescience.com/16953-brain-body-size-expense.html 

The Golden Age of Intelligence?

Busts of Greek philosophers (Wikicommons, Matt Neale). Did the Ancient Greeks have the highest mean IQ of any human population then and since?



Francis Galton argued that average intelligence had been much higher in ancient Greece than in modern England. He came to this conclusion after comparing the proportion of eminent men in Athens of the fifth century BC with the proportion of eminent men in the England of his day:

It follows from all this, that the average ability of the Athenian race is, on the lowest possible estimate, very nearly two grades higher than our own-that is, about as much as our race is above that of the African negro.(Galton 1869, p. 342)

This high ability was then presumably lost:

We know, and may guess something more, of the reason why this marvellously-gifted race declined. Social morality grew exceedingly lax; marriage became unfashionable, and was avoided; many of the more ambitious and accomplished women were avowed courtesans, and consequently infertile, and the mothers of the incoming population were of a heterogeneous class. (Galton 1869, pp. 342-343)

If we accept Galton's reasoning, Ancient Greeks had the highest mean IQ of any human population, something like 120 or 125. By comparison, Ashkenazi Jews have an estimated mean IQ of 110. But was Galton right? His calculations were criticized at the time, specifically for underestimating the number of Athenian citizens. He consequently revised his calculation downward to 1.5 grades higher, i.e., a mean IQ of 115 to 119 (Challis 2013, p. 56).

That's still impressive. But higher IQ doesn't necessarily imply higher innate intelligence. Conditions in ancient Greece may have simply been better for intellectual discussion, such activity being respected as an activity in its own right. By comparison, intellectual discussion was much more circumscribed in the ancient Middle East, where it was confined to specific people who performed specific duties, most often writing and copying texts at the request of others.

Admittedly, this explanation does not exclude a genetic one. If the cultural environment favors intellectual development, it will tend to reward the most promising people with reproductive success. A scribe is thus praised in a Jewish wisdom book from the second century BC: "Many will praise his understanding; it will never be blotted out. His memory will not disappear, and his name will live through all generations. Nations will speak of his wisdom, and the congregation will proclaim his praise. If he lives long, he will leave a name greater than a thousand." Book of Sirach [39.1-11].

In the ancient world, 'leaving a great name' did not mean being written about by historians but rather having many illustrious children to carry on the family name long after death. Intellectual ability thus co-evolved with a supportive cultural base. Indeed, we humans have co-evolved much more with our cultural environment than with our natural environment (Hawks et al. 2007).


A new yardstick

Galton's conjecture can now be tested with two new research tools:

1. Ancient DNA. Large quantities of genetic data have been collected from ancient human remains and are now being made available to researchers. This year, the Reich lab at the Harvard Medical School released over 2,000 ancient genomes, including 30 from ancient Greece.

2. Polygenic cognitive score. Some gene loci are associated with differences in educational attainment. By examining the variants at these loci and by adding up the ones associated with higher educational attainment, we can calculate a polygenic score that correlates with mean IQ (r = 0.98).

By examining 102 ancient genomes, a research team led by Michael Woodley of Menie was able to chart the evolution of cognitive ability in Europe and Central Asia. His team found that genetic variants for higher educational attainment gradually increased in frequency from 4,560 to 1,210 years ago (Woodley of Menie et al. 2017). Now, with newly released data from the Reich lab, he is leading a research effort to look specifically at ancient Greeks. The results are still preliminary, but they indicate a progressive increase in the polygenic score from Neolithic to Mycenaean times, followed by a decrease. When? We don't know because we lack post-Mycenaean data (Woodley of Menie et al. 2019).


More to come ...

This is a promising avenue for research. In particular, we need:

- A larger sample of modern Greek genomes. This should not be difficult.

- Samples from post-Mycenaean times to the end of Ottoman rule. Was Galton right in placing this cognitive decline during the ensuing Hellenistic and Roman periods? Or did it happen over a longer span of time?

The final published paper should explain at greater length the research team's use of a restricted polygenic score, i.e., a polygenic score based only on those genetic variants that seem causally related to high educational attainment, and not simply associated with high educational attainment. This approach is acceptable if a third party had identified these variants; otherwise, there is a risk of focusing on those variants that support Galton's hypothesis.

Another point: in the presentation of his new project, Woodley of Menie spoke repeatedly about population replacement at various times in the history of ancient Greece (Woodley of Menie et al. 2019). Yet the current thinking is that immigration was historically unimportant in Greece. Present-day Greeks are largely descended from the Mycenaeans, with some later introgression by Slavic tribes and other peoples (Gibbons 2017; Stamatoyannopoulos et al. 2017).

This research is especially exciting because the Reich lab released ancient DNA data not only from ancient Greece but also from elsewhere. History may end up being seen in a new light. For instance:

- Rome probably went through a similar increase in mean intelligence, followed by decline. When did the decline begin? During the collapse of the fifth century? I suspect earlier, perhaps in the third century. The barbarian invasions were both a cause and effect in the collapse of Roman civilization.

- The Enlightenment was due only in part to things like the invention of the printing press, the voyages of discovery, and the founding of universities. These were subsidiary causes that resulted from and supported a more fundamental change: a steady increase in the smart fraction of European societies—the proportion of people who enjoy reading, writing and, above all, thinking.


References

Angel, J.L. (1950). Population size and microevolution in Greece. Cold Spring Harbor Symposia on Quantitative Biology 15: 343-351. doi:10.1101/SQB.1950.015.01.031

Challis, D. (2013). The Archaeology of Race. The Eugenic Ideas of Francis Galton and Flinders Petrie. London: Bloomsbury.
https://www.academia.edu/1520119/Archaeology_of_Race._The_Eugenic_Ideas_of_Francis_Galton_and_Flinders_Petrie_Bloomsbury_2013_ 

Galton, F. (1869). Hereditary Genius: An Inquiry into Its Laws and Consequences. London: MacMillan.
http://galton.org/books/hereditary-genius/

Gibbons, A. (2017). The Greeks really do have near-mythical origins, ancient DNA reveals. Science August 2
https://www.sciencemag.org/news/2017/08/greeks-really-do-have-near-mythical-origins-ancient-dna-reveals 

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) 104: 20753-20758.
https://www.researchgate.net/profile/Henry_Harpending/publication/5761823_Recent_Acceleration_of_Human_Adaptive_Evolution/links/0c9605240c4bb57b55000000.pdf  
Stamatoyannopoulos, G., A. Bose, A. Teodosiadis, F. Tsetsos, A. Plantinga, N. Psatha, N. Zogas, E. Yannaki, P. Zalloua, K.K. Kidd, B.L. Browning, J. Stamatoyannopoulos, P. Paschou, P. Drineas et al. (2017). Genetics of the peloponnesean populations and the theory of extinction of the medieval peloponnesean Greeks. European Journal of Human Genetics 25: 637-645.
https://www.nature.com/articles/ejhg201718 

Woodley of Menie, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: Comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280
https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/holocene-selection-for-variants-associated-with-general-cognitive-ability-comparing-ancient-and-modern-genomes/BF2A35F0D4F565757875287E59A1F534

Woodley of Menie, M.A., J. Delhez, M. Peñaherrera-Aguirre, and E.O.W. Kirkegaard. (2019). Cognitive archeogenetics of ancient and modern Greeks. London Conference on Intelligence 
https://www.youtube.com/watch?v=UES_tpDxz9A