When Did Black People Evolve?

In previous posts, we discussed the evolution of Whites and Asians, so today we’re taking a look at people from Sub-Saharan Africa.

Modern humans only left Africa about 100,000 to 70,000 yeas ago, and split into Asians and Caucasians around 40,000 years ago. Their modern appearances came later–white skin, light hair and light eyes, for example, only evolved in the past 20,000 and possibly within the past 10,000 years.

What about the Africans, or specifically, Sub-Saharans? (North Africans, like Tunisians and Moroccans, are in the Caucasian clade.) When did their phenotypes evolve?

The Sahara, an enormous desert about the size of the United States, is one of the world’s biggest, most ancient barriers to human travel. The genetic split between SSAs and non-SSAs, therefore, is one of the oldest and most substantial among human populations. But there are even older splits within Africa–some of the ancestors of today’s Pygmies and Bushmen may have split off from other Africans 200,000-300,000 years ago. We’re not sure, because the study of archaic African DNA is still in its infancy.

Some anthropologists refer to Bushmen as “gracile,” which means they are a little shorter than average Europeans and not stockily built

The Bushmen present an interesting case, because their skin is quite light (for Africans.) I prefer to call it golden. The nearby Damara of Namibia, by contrast, are one of the world’s darkest peoples. (The peoples of South Sudan, eg Malik Agar, may be darker, though.) The Pygmies are the world’s shortest peoples; the peoples of South Sudan, such as the Dinka and Shiluk, are among the world’s tallest.

Sub-Saharan Africa’s ethnic groups can be grouped, very broadly, into Bushmen, Pygmies, Bantus (aka Niger-Congo), Nilotics, and Afro-Asiatics. Bushmen and Pygmies are extremely small groups, while Bantus dominate the continent–about 85% of Sub Saharan Africans speak a language from the Niger-Congo family. The Afro-Asiatic groups, as their name implies, have had extensive contact with North Africa and the Middle East.

Most of America’s black population hails from West Africa–that is, the primarily Bantu region. The Bantus and similar-looking groups among the Nilotics and Afro-Asiatics (like the Hausa) are, therefore, have both Africa’s most iconic and most common phenotypes.

For the sake of this post, we are not interested in the evolution of traits common to all humans, such as bipedalism. We are only interested in those traits generally shared by most Sub-Saharans and generally not shared by people outside of Africa.

detailed map of African and Middle Eastern ethnicities in Haaks et al’s dataset

One striking trait is black hair: it is distinctively “curly” or “frizzy.” Chimps and gorrilas do not have curly hair. Neither do whites and Asians. (Whites and Asians, therefore, more closely resemble chimps in this regard.) Only Africans and a smattering of other equatorial peoples like Melanesians have frizzy hair.

Black skin is similarly distinct. Chimps, who live in the shaded forest and have fur, do not have high levels of melanin all over their bodies. While chimps naturally vary in skin tone, an unfortunate, hairless chimp is practically “white.

Humans therefore probably evolved both black skin and frizzy hair at about the same time–when we came out of the shady forests and began running around on the much sunnier savannahs. Frizzy hair seems well-adapted to cooling–by standing on end, it lets air flow between the follicles–and of course melanin is protective from the sun’s rays. (And apparently, many of the lighter-skinned Bushmen suffer from skin cancer.)

Steatopygia also comes to mind, though I don’t know if anyone has studied its origins.

According to Wikipedia, additional traits common to Sub-Saharan Africans include:

In modern craniofacial anthropometry, Negroid describes features that typify skulls of black people. These include a broad and round nasal cavity; no dam or nasal sill; Quonset hut-shaped nasal bones; notable facial projection in the jaw and mouth area (prognathism); a rectangular-shaped palate; a square or rectangular eye orbit shape;[21] a large interorbital distance; a more undulating supraorbital ridge;[22] and large, megadontic teeth.[23] …

Modern cross-analysis of osteological variables and genome-wide SNPs has identified specific genes, which control this craniofacial development. Of these genes, DCHS2, RUNX2, GLI3, PAX1 and PAX3 were found to determine nasal morphology, whereas EDAR impacts chin protrusion.[27] …

Ashley Montagu lists “neotenous structural traits in which…Negroids [generally] differ from Caucasoids… flattish nose, flat root of the nose, narrower ears, narrower joints, frontal skull eminences, later closure of premaxillarysutures, less hairy, longer eyelashes, [and] cruciform pattern of second and third molars.”[28]

The Wikipedia page on Dark Skin states:

As hominids gradually lost their fur (between 4.5 and 2 million years ago) to allow for better cooling through sweating, their naked and lightly pigmented skin was exposed to sunlight. In the tropics, natural selection favoured dark-skinned human populations as high levels of skin pigmentation protected against the harmful effects of sunlight. Indigenous populations’ skin reflectance (the amount of sunlight the skin reflects) and the actual UV radiation in a particular geographic area is highly correlated, which supports this idea. Genetic evidence also supports this notion, demonstrating that around 1.2 million years ago there was a strong evolutionary pressure which acted on the development of dark skin pigmentation in early members of the genus Homo.[25]

About 7 million years ago human and chimpanzee lineages diverged, and between 4.5 and 2 million years ago early humans moved out of rainforests to the savannas of East Africa.[23][28] They not only had to cope with more intense sunlight but had to develop a better cooling system. …

Skin colour is a polygenic trait, which means that several different genes are involved in determining a specific phenotype. …

Data collected from studies on MC1R gene has shown that there is a lack of diversity in dark-skinned African samples in the allele of the gene compared to non-African populations. This is remarkable given that the number of polymorphisms for almost all genes in the human gene pool is greater in African samples than in any other geographic region. So, while the MC1Rf gene does not significantly contribute to variation in skin colour around the world, the allele found in high levels in African populations probably protects against UV radiation and was probably important in the evolution of dark skin.[57][58]

Skin colour seems to vary mostly due to variations in a number of genes of large effect as well as several other genes of small effect (TYR, TYRP1, OCA2, SLC45A2, SLC24A5, MC1R, KITLG and SLC24A4). This does not take into account the effects of epistasis, which would probably increase the number of related genes.[59] Variations in the SLC24A5 gene account for 20–25% of the variation between dark and light skinned populations of Africa,[60] and appear to have arisen as recently as within the last 10,000 years.[61] The Ala111Thr or rs1426654 polymorphism in the coding region of the SLC24A5 gene reaches fixation in Europe, and is also common among populations in North Africa, the Horn of Africa, West Asia, Central Asia and South Asia.[62][63][64]

That’s rather interesting about MC1R. It could imply that the difference in skin tone between SSAs and non-SSAs is due to active selection in Blacks for dark skin and relaxed selection in non-Blacks, rather than active selection for light skin in non-Blacks.

The page on MC1R states:

MC1R is one of the key proteins involved in regulating mammalianskin and hair color. …It works by controlling the type of melanin being produced, and its activation causes the melanocyte to switch from generating the yellow or red phaeomelanin by default to the brown or black eumelanin in replacement. …

This is consistent with active selection being necessary to produce dark skin, and relaxed selection producing lighter tones.

Studies show the MC1R Arg163Gln allele has a high frequency in East Asia and may be part of the evolution of light skin in East Asian populations.[40] No evidence is known for positive selection of MC1R alleles in Europe[41] and there is no evidence of an association between MC1R and the evolution of light skin in European populations.[42] The lightening of skin color in Europeans and East Asians is an example of convergent evolution.

However, we should also note:

Dark-skinned people living in low sunlight environments have been recorded to be very susceptible to vitamin D deficiency due to reduced vitamin D synthesis. A dark-skinned person requires about six times as much UVB than lightly pigmented persons.

PCA graph and map of sampling locations. Modern people are indicated with gray circles.

Unfortunately, most of the work on human skin tones has been done among Europeans (and, oddly, zebra fish,) limiting our knowledge about the evolution of African skin tones, which is why this post has been sitting in my draft file for months. Luckily, though, two recent studies–Loci Associated with Skin Pigmentation Identified in African Populations and Reconstructing Prehistoric African Population Structure–have shed new light on African evolution.

In Reconstructing Prehistoric African Population Structure, Skoglund et al assembled genetic data from 16 prehistoric Africans and compared them to DNA from nearby present-day Africans. They found:

  1. The ancestors of the Bushmen (aka the San/KhoiSan) once occupied a much wider area.
  2. They contributed about 2/3s of the ancestry of ancient Malawi hunter-gatherers (around 8,100-2,500 YA)
  3. Contributed about 1/3 of the ancestry of ancient Tanzanian hunter-gatherers (around 1,400 YA)
  4. Farmers (Bantus) spread from west Africa, completely replacing hunter-gatherers in some areas
  5. Modern Malawians are almost entirely Bantu.
  6. A Tanzanian pastoralist population from 3,100 YA spread out across east Africa and into southern Africa
  7. Bushmen ancestry was not found in modern Hadza, even though they are hunter-gatherers and speak a click language like the Bushmen.
  8. The Hadza more likely derive most of their ancestry from ancient Ethiopians
  9. Modern Bantu-speakers in Kenya derive from a mix between western Africans and Nilotics around 800-400 years ago.
  10. Middle Eastern (Levant) ancestry is found across eastern Africa from an admixture event that occurred around 3,000 YA, or around the same time as the Bronze Age Collapse.
  11. A small amount of Iranian DNA arrived more recently in the Horn of Africa
  12. Ancient Bushmen were more closely related to modern eastern Africans like the Dinka (Nilotics) and Hadza than to modern west Africans (Bantus),
  13. This suggests either complex relationships between the groups or that some Bantus may have had ancestors from an unknown group of humans more ancient than the Bushmen.
  14. Modern Bushmen have been evolving darker skins
  15. Pygmies have been evolving shorter stature
Automated clustering of ancient and modern populations (moderns in gray)

I missed #12-13 on my previous post about this paper, though I did note that the more data we get on ancient African groups, the more likely I think we are to find ancient admixture events. If humans can mix with Neanderthals and Denisovans, then surely our ancestors could have mixed with Ergaster, Erectus, or whomever else was wandering around.

Distribution of ancient Bushmen and Ethiopian DNA in south and east Africa

#15 is interesting, and consistent with the claim that Bushmen suffer from a lot of skin cancer–before the Bantu expansion, they lived in far more forgiving climates than the Kalahari desert. But since Bushmen are already lighter than their neighbors, this begs the question of how light their ancestors–who had no Levantine admixture–were. Could the Bantus’ and Nilotics’ darker skins have evolved after the Bushmen/everyone else split?

Meanwhile, in Loci Associated with Skin Pigmentation Identified in African Populations, Crawford et al used genetic samples from 1,570 people from across Africa to find six genetic areas–SLC24A5, MFSD12, DDB1, TMEM138, OCA2 and HERC2–which account for almost 30% of the local variation in skin color.

Bantu (green) and Levantine/pastoralist DNA in modern peoples

SLC24A5 is a light pigment introduced to east Africa from the Levant, probably around 3,000 years ago. Today, it is common in Ethiopia and Tanzania.

Interestingly, according to the article, “At all other loci, variants associated with dark pigmentation in Africans are identical by descent in southern Asian and Australo-Melanesian populations.”

These are the world’s other darkest peoples, such as the Jarawas of the Andaman Islands or the Melanesians of Bougainville, PNG. (And, I assume, some groups from India such as the Tamils.) This implies that these groups 1. had dark skin already when they left Africa, and 2. Never lost it on their way to their current homes. (If they had gotten lighter during their journey and then darkened again upon arrival, they likely would have different skin color variants than their African cousins.)

This implies that even if the Bushmen split off (around 200,000-300,000 YA) before dark skin evolved, it had evolved by the time people left Africa and headed toward Australia (around 100,000-70,000 YA.) This gives us a minimum threshold: it most likely evolved before 70,000 YA.

(But as always, we should be careful because perhaps there are even more skin color variant that we don’t know about yet in these populations.)

MFSD12 is common among Nilotics and is related to darker skin.

And according to the abstract, which Razib Khan posted:

Further, the alleles associated with skin pigmentation at all loci but SLC24A5 are ancient, predating the origin of modern humans. The ancestral alleles at the majority of predicted causal SNPs are associated with light skin, raising the possibility that the ancestors of modern humans could have had relatively light skin color, as is observed in the San population today.

The full article is not out yet, so I still don’t know when all of these light and dark alleles emerged, but the order is absolutely intriguing. For now, it looks like this mystery will still have to wait.



Two Exciting Papers on African Genetics

I loved that movie
Nǃxau ǂToma, (aka Gcao Tekene Coma,) Bushman star of “The Gods Must be Crazy,” roughly 1944-2003

An interesting article on Clues to Africa’s Mysterious Past appeared recently in the NY Times:

It was only two years ago that researchers found the first ancient human genome in Africa: a skeleton in a cave in Ethiopia yielded DNA that turned out to be 4,500 years old.

On Thursday, an international team of scientists reported that they had recovered far older genes from bone fragments in Malawi dating back 8,100 years. The researchers also retrieved DNA from 15 other ancient people in eastern and southern Africa, and compared the genes to those of living Africans.

Let’s skip to the article, Reconstructing Prehistoric African Population Structure by Skoglund et al:

We assembled genome-wide data from 16 prehistoric Africans. We show that the anciently divergent lineage that comprises the primary ancestry of the southern African San had a wider distribution in the past, contributing approximately two-thirds of the ancestry of Malawi hunter-gatherers ∼8,100–2,500 years ago and approximately one-third of the ancestry of Tanzanian hunter-gatherers ∼1,400 years ago.

Paths of the great Bantu Migration

The San are also known as the Bushmen, a famous group of recent hunter-gatherers from southern Africa.

We document how the spread of farmers from western Africa involved complete replacement of local hunter-gatherers in some regions…

This is most likely the Great Bantu Migration, which I wrote about in Into Africa: the Great Bantu Migration.

…and we track the spread of herders by showing that the population of a ∼3,100-year-old pastoralist from Tanzania contributed ancestry to people from northeastern to southern Africa, including a ∼1,200-year-old southern African pastoralist…

Whereas the two individuals buried in ∼2,000 BP hunter-gatherer contexts in South Africa share ancestry with southern African Khoe-San populations in the PCA, 11 of the 12 ancient individuals who lived in eastern and south-central Africa between ∼8,100 and ∼400 BP form a gradient of relatedness to the eastern African Hadza on the one hand and southern African Khoe-San on the other (Figure 1A).

The Hadza are a hunter-gatherer group from Tanzania who are not obviously related to any other people. Their language has traditionally been classed alongside the languages of the KhoiSan/Bushmen people because they all contain clicks, but the languages otherwise have very little in common and Hadza appears to be a language isolate, like Basque.

The genetic cline correlates to geography, running along a north-south axis with ancient individuals from Ethiopia (∼4,500 BP), Kenya (∼400 BP), Tanzania (both ∼1,400 BP), and Malawi (∼8,100–2,500 BP), showing increasing affinity to southern Africans (both ancient individuals and present-day Khoe-San). The seven individuals from Malawi show no clear heterogeneity, indicating a long-standing and distinctive population in ancient Malawi that persisted for at least ∼5,000 years (the minimum span of our radiocarbon dates) but which no longer exists today. …

We find that ancestry closely related to the ancient southern Africans was present much farther north and east in the past than is apparent today. This ancient southern African ancestry comprises up to 91% of the ancestry of Khoe-San groups today (Table S5), and also 31% ± 3% of the ancestry of Tanzania_Zanzibar_1400BP, 60% ± 6% of the ancestry of Malawi_Fingira_6100BP, and 65% ± 3% of the ancestry of Malawi_Fingira_2500BP (Figure 2A). …

Both unsupervised clustering (Figure 1B) and formal ancestry estimation (Figure 2B) suggest that individuals from the Hadza group in Tanzania can be modeled as deriving all their ancestry from a lineage related deeply to ancient eastern Africans such as the Ethiopia_4500BP individual …

So what’s up with the Tanzanian expansion mentioned in the summary?

Western-Eurasian-related ancestry is pervasive in eastern Africa today … and the timing of this admixture has been estimated to be ∼3,000 BP on average… We found that the ∼3,100 BP individual… associated with a Savanna Pastoral Neolithic archeological tradition, could be modeled as having 38% ± 1% of her ancestry related to the nearly 10,000-year-old pre-pottery farmers of the Levant These results could be explained by migration into Africa from descendants of pre-pottery Levantine farmers or alternatively by a scenario in which both pre-pottery Levantine farmers and Tanzania_Luxmanda_3100BP descend from a common ancestral population that lived thousands of years earlier in Africa or the Near East. We fit the remaining approximately two-thirds of Tanzania_Luxmanda_3100BP as most closely related to the Ethiopia_4500BP…

…present-day Cushitic speakers such as the Somali cannot be fit simply as having Tanzania_Luxmanda_3100BP ancestry. The best fitting model for the Somali includes Tanzania_Luxmanda_3100BP ancestry, Dinka-related ancestry, and 16% ± 3% Iranian-Neolithic-related ancestry (p = 0.015). This suggests that ancestry related to the Iranian Neolithic appeared in eastern Africa after earlier gene flow related to Levant Neolithic populations, a scenario that is made more plausible by the genetic evidence of admixture of Iranian-Neolithic-related ancestry throughout the Levant by the time of the Bronze Age …and in ancient Egypt by the Iron Age …

There is then a discussion of possible models of ancient African population splits (were the Bushmen the first? How long have they been isolated?) I suspect the more ancient African DNA we uncover, the more complicated the tree will become, just as in Europe and Asia we’ve discovered Neanderthal and Denisovan admixture.

They also compared genomes to look for genetic adaptations and found evidence for selection for taste receptors and “response to radiation” in the Bushmen, which the authors note “could be due to exposure to sunlight associated with the life of the ‡Khomani and Ju|’hoan North people in the Kalahari Basin, which has become a refuge for hunter-gatherer populations in the last millenia due to encroachment by pastoralist and agriculturalist groups.”

(The Bushmen are lighter than Bantus, with a more golden or tan skin tone.)

They also found evidence of selection for short stature among the Pygmies (which isn’t really surprising to anyone, unless you thought they had acquired their heights by admixture with another very short group of people.)

Overall, this is a great paper and I encourage you to RTWT, especially the pictures/graphs.

Now, if that’s not enough African DNA for you, we also have Loci Associated with Skin Pigmentation Identified in African Populations, by Crawford et al:

Examining ethnically diverse African genomes, we identify variants in or near SLC24A5, MFSD12, DDB1, TMEM138, OCA2 and HERC2 that are significantly associated with skin pigmentation. Genetic evidence indicates that the light pigmentation variant at SLC24A5 was introduced into East Africa by gene flow from non-Africans. At all other loci, variants associated with dark pigmentation in Africans are identical by descent in southern Asian and Australo-Melanesian populations. Functional analyses indicate that MFSD12 encodes a lysosomal protein that affects melanogenesis in zebrafish and mice, and that mutations in melanocyte-specific regulatory regions near DDB1/TMEM138 correlate with expression of UV response genes under selection in Eurasians.

I’ve had an essay on the evolution of African skin tones sitting in my draft folder for ages because this research hadn’t been done. There’s plenty of research on European and Asian skin tones (skin appears to have significantly lightened around 10,000 years ago in Europeans,) but much less on Africans. Luckily for me, this paper fixes that.

Looks like SLC24A5 is related to that Levantine/Iranian back-migration into Africa documented in the first paper.

Are “Nerds” Just a Hollywood Stereotype?

Yes, MIT has a football team.

The other day on Twitter, Nick B. Steves challenged me to find data supporting or refuting his assertion that Nerds vs. Jocks is a false stereotype, invented around 1975. Of course, we HBDers have a saying–“all stereotypes are true,” even the ones about us–but let’s investigate Nick’s claim and see where it leads us.

(NOTE: If you have relevant data, I’d love to see it.)

Unfortunately, terms like “nerd,” “jock,” and “chad” are not all that well defined. Certainly if we define “jock” as “athletic but not smart” and nerd as “smart but not athletic,” then these are clearly separate categories. But what if there’s a much bigger group of people who are smart and athletic?

Or what if we are defining “nerd” and “jock” too narrowly? Wikipedia defines nerd as, “a person seen as overly intellectual, obsessive, or lacking social skills.” I recall a study–which I cannot find right now–which found that nerds had, overall, lower-than-average IQs, but that study included people who were obsessive about things like comic books, not just people who majored in STEM. Similarly, should we define “jock” only as people who are good at sports, or do passionate sports fans count?

For the sake of this post, I will define “nerd” as “people with high math/science abilities” and “jock” as “people with high athletic abilities,” leaving the matter of social skills undefined. (People who merely like video games or watch sports, therefore, do not count.)

Nick is correct on one count: according to Wikipedia, although the word “nerd” has been around since 1951, it was popularized during the 70s by the sitcom Happy Days. However, Wikipedia also notes that:

An alternate spelling,[10] as nurd or gnurd, also began to appear in the mid-1960s or early 1970s.[11] Author Philip K. Dick claimed to have coined the nurd spelling in 1973, but its first recorded use appeared in a 1965 student publication at Rensselaer Polytechnic Institute.[12][13] Oral tradition there holds that the word is derived from knurd (drunk spelled backward), which was used to describe people who studied rather than partied. The term gnurd (spelled with the “g”) was in use at the Massachusetts Institute of Technology by 1965.[14] The term nurd was also in use at the Massachusetts Institute of Technology as early as 1971 but was used in the context for the proper name of a fictional character in a satirical “news” article.[15]

suggesting that the word was already common among nerds themselves before it was picked up by TV.

But we can trace the nerd-jock dichotomy back before the terms were coined: back in 1921, Lewis Terman, a researcher at Stanford University, began a long-term study of exceptionally high-IQ children, the Genetic Studies of Genius aka the Terman Study of the Gifted:

Terman’s goal was to disprove the then-current belief that gifted children were sickly, socially inept, and not well-rounded.

This belief was especially popular in a little nation known as Germany, where it inspired people to take schoolchildren on long hikes in the woods to keep them fit and the mass-extermination of Jews, who were believed to be muddying the German genepool with their weak, sickly, high-IQ genes (and nefariously trying to marry strong, healthy German in order to replenish their own defective stock.) It didn’t help that German Jews were both high-IQ and beset by a number of illnesses (probably related to high rates of consanguinity,) but then again, the Gypsies are beset by even more debilitating illnesses, but no one blames this on all of the fresh air and exercise afforded by their highly mobile lifestyles.

(Just to be thorough, though, the Nazis also exterminated the Gypsies and Hans Asperger’s subjects, despite Asperger’s insistence that they were very clever children who could probably be of great use to the German war effort via code breaking and the like.)

The results of Terman’s study are strongly in Nick’s favor. According to Psychology Today’s  account:

His final group of “Termites” averaged a whopping IQ of 151. Following-up his group 35-years later, his gifted group at mid-life definitely seemed to conform to his expectations. They were taller, healthier, physically better developed, and socially adept (dispelling the myth at the time of high-IQ awkward nerds).

According to Wikipedia:

…the first volume of the study reported data on the children’s family,[17] educational progress,[18] special abilities,[19] interests,[20] play,[21] and personality.[22] He also examined the children’s racial and ethnic heritage.[23] Terman was a proponent of eugenics, although not as radical as many of his contemporary social Darwinists, and believed that intelligence testing could be used as a positive tool to shape society.[3]

Based on data collected in 1921–22, Terman concluded that gifted children suffered no more health problems than normal for their age, save a little more myopia than average. He also found that the children were usually social, were well-adjusted, did better in school, and were even taller than average.[24] A follow-up performed in 1923–1924 found that the children had maintained their high IQs and were still above average overall as a group.

Of course, we can go back even further than Terman–in the early 1800s, allergies like hay fever were associated with the nobility, who of course did not do much vigorous work in the fields.

My impression, based on studies I’ve seen previously, is that athleticism and IQ are positively correlated. That is, smarter people tend to be more athletic, and more athletic people tend to be smarter. There’s a very obvious reason for this: our brains are part of our bodies, people with healthier bodies therefore also have healthier brains, and healthier brains tend to work better.

At the very bottom of the IQ distribution, mentally retarded people tend to also be clumsy, flacid, or lacking good muscle tone. The same genes (or environmental conditions) that make children have terrible health/developmental problems often also affect their brain growth, and conditions that affect their brains also affect their bodies. As we progress from low to average to above-average IQ, we encounter increasingly healthy people.

In most smart people, high-IQ doesn’t seem to be a random fluke, a genetic error, nor fitness reducing: in a genetic study of children with exceptionally high IQs, researchers failed to find many genes that specifically endowed the children with genius, but found instead a fortuitous absence of deleterious genes that knock a few points off the rest of us. The same genes that have a negative effect on the nerves and proteins in your brain probably also have a deleterious effect on the nerves and proteins throughout the rest of your body.

And indeed, there are many studies which show a correlation between intelligence and strength (eg, Longitudinal and Cross-Sectional Assessments of Age Changes in Physical Strength as Related to Sex, Social Class, and Mental Ability) or intelligence and overall health/not dying (eg, Intelligence in young adulthood and cause-specific mortality in the Danish Conscription Database (pdf) and The effects of occupation-based social position on mortality in a large American cohort.)

On the other hand, the evolutionary standard for “fitness” isn’t strength or longevity, but reproduction, and on this scale the high-IQ don’t seem to do as well:

Smart teens don’t have sex (or kiss much either): (h/t Gene Expresion)

Controlling for age, physical maturity, and mother’s education, a significant curvilinear relationship between intelligence and coital status was demonstrated; adolescents at the upper and lower ends of the intelligence distribution were less likely to have sex. Higher intelligence was also associated with postponement of the initiation of the full range of partnered sexual activities. … Higher intelligence operates as a protective factor against early sexual activity during adolescence, and lower intelligence, to a point, is a risk factor.


Here we see the issue plainly: males at 120 and 130 IQ are less likely to get laid than clinically retarded men in 70s and 60s. The right side of the graph are “nerds”, the left side, “jocks.” Of course, the high-IQ females are even less likely to get laid than the high-IQ males, but males tend to judge themselves against other men, not women, when it comes to dating success. Since the low-IQ females are much less likely to get laid than the low-IQ males, this implies that most of these “popular” guys are dating girls who are smarter than themselves–a fact not lost on the nerds, who would also like to date those girls.

 In 2001, the MIT/Wellesley magazine Counterpart (Wellesley is MIT’s “sister school” and the two campuses allow cross-enrollment in each other’s courses) published a sex survey that provides a more detailed picture of nerd virginity:

I’m guessing that computer scientists invented polyamory, and neuroscientists are the chads of STEM. The results are otherwise pretty predictable.

Unfortunately, Counterpoint appears to be defunct due to lack of funding/interest and I can no longer find the original survey, but here is Jason Malloy’s summary from Gene Expression:

By the age of 19, 80% of US males and 75% of women have lost their virginity, and 87% of college students have had sex. But this number appears to be much lower at elite (i.e. more intelligent) colleges. According to the article, only 56% of Princeton undergraduates have had intercourse. At Harvard 59% of the undergraduates are non-virgins, and at MIT, only a slight majority, 51%, have had intercourse. Further, only 65% of MIT graduate students have had sex.

The student surveys at MIT and Wellesley also compared virginity by academic major. The chart for Wellesley displayed below shows that 0% of studio art majors were virgins, but 72% of biology majors were virgins, and 83% of biochem and math majors were virgins! Similarly, at MIT 20% of ‘humanities’ majors were virgins, but 73% of biology majors. (Apparently those most likely to read Darwin are also the least Darwinian!)

College Confidential has one paragraph from the study:

How Rolling Stone-ish are the few lucky souls who are doing the horizontal mambo? Well, not very. Considering all the non-virgins on campus, 41% of Wellesley and 32% of MIT students have only had one partner (figure 5). It seems that many Wellesley and MIT students are comfortingly monogamous. Only 9% of those who have gotten it on at MIT have been with more than 10 people and the number is 7% at Wellesley.

Someone needs to find the original study and PUT IT BACK ON THE INTERNET.

But this lack of early sexual success seems to translate into long-term marital happiness, once nerds find “the one.”Lex Fridman’s Divorce Rates by Profession offers a thorough list. The average divorce rate was 16.35%, with a high of 43% (Dancers) and a low of 0% (“Media and communication equipment workers.”)

I’m not sure exactly what all of these jobs are nor exactly which ones should count as STEM (veterinarian? anthropologists?) nor do I know how many people are employed in each field, but I count 49 STEM professions that have lower than average divorce rates (including computer scientists, economists, mathematical science, statisticians, engineers, biologists, chemists, aerospace engineers, astronomers and physicists, physicians, and nuclear engineers,) and only 23 with higher than average divorce rates (including electricians, water treatment plant operators, radio and telecommunication installers, broadcast engineers, and similar professions.) The purer sciences obviously had lower rates than the more practical applied tech fields.

The big outliers were mathematicians (19.15%), psychologists (19.26%), and sociologists (23.53%), though I’m not sure they count (if so, there were only 22 professions with higher than average divorce rates.)

I’m not sure which professions count as “jock” or “chad,” but athletes had lower than average rates of divorce (14.05%) as did firefighters, soldiers, and farmers. Financial examiners, hunters, and dancers, (presumably an athletic female occupation) however, had very high rates of divorce.

Medical Daily has an article on Who is Most Likely to Cheat? The Top 9 Jobs Unfaithful People Have (according to survey):

According to the survey recently taken by the “infidelity dating website,” Victoria Milan, individuals working in the finance field, such as brokers, bankers, and analysts, are more likely to cheat than those in any other profession. However, following those in finance comes those in the aviation field, healthcare, business, and sports.

With the exception of healthcare and maybe aviation, these are pretty typical Chad occupations, not STEM.

The Mirror has a similar list of jobs where people are most and least likely to be married. Most likely: Dentist, Chief Executive, Sales Engineer, Physician, Podiatrist, Optometrist, Farm product buyer, Precision grinder, Religious worker, Tool and die maker.

Least likely: Paper-hanger, Drilling machine operator, Knitter textile operator, Forge operator, Mail handler, Science technician, Practical nurse, Social welfare clerk, Winding machine operative, Postal clerk.

I struggled to find data on male fertility by profession/education/IQ, but there’s plenty on female fertility, eg the deceptively titled High-Fliers have more Babies:

…American women without any form of high-school diploma have a fertility rate of 2.24 children. Among women with a high-school diploma the fertility rate falls to 2.09 and for women with some form of college education it drops to 1.78.

However, among women with college degrees, the economists found the fertility rate rises to 1.88 and among women with advanced degrees to 1.96. In 1980 women who had studied for 16 years or more had a fertility rate of just 1.2.

As the economists prosaically explain: “The relationship between fertility and women’s education in the US has recently become U-shaped.”

Here is another article about the difference in fertility rates between high and low-IQ women.

But female fertility and male fertility may not be the same–I recall data elsewhere indicating that high-IQ men have more children than low IQ men, which implies those men are having their children with low-IQ women. (For example, while Bill and Hillary seem about matched on IQ, and have only one child, Melania Trump does not seem as intelligent as Trump, who has five children.)

Amusingly, I did find data on fertility rate by father’s profession for 1920, in the Birth Statistics for the Birth Registration Area of the US:

Of the 1,508,874 children born in 1920 in the birth registration area of the United states, occupations of fathers are stated for … 96.9%… The average number of children ever born to the present wives of these occupied fathers is 3.3 and the average number of children living 2.9.

The average number of children ever born ranges from 4.6 for foremen, overseers, and inspectors engaged in the extraction of minerals to 1.8 for soldiers, sailors, and marines. Both of these extreme averages are easily explained, for soldier, sailors and marines are usually young, while such foremen, overseers, and inspectors are usually in middle life. For many occupations, however, the ages of the fathers are presumably about the same and differences shown indicate real differences in the size of families. For example, the low figure for dentists, (2), architects, (2.1), and artists, sculptors, and teachers of art (2.2) are in striking contrast with the figure for mine operatives (4.3), quarry operatives (4.1) bootblacks, and brick and stone masons (each 3.9). …

As a rule the occupations credited with the highest number of children born are also credited with the highest number of children living, the highest number of children living appearing for foremen, overseers, and inspectors engaged in the extraction of minerals (3.9) and for steam and street railroad foremen and overseer (3.8), while if we exclude groups plainly affected by the age of fathers, the highest number of children living appear for mine and quarry operatives (each 3.6).

Obviously the job market was very different in 1920–no one was majoring in computer science. Perhaps some of those folks who became mine and quarry operatives back then would become engineers today–or perhaps not. Here are the average numbers of surviving children for the most obviously STEM professions (remember average for 1920 was 2.9):

Electricians 2.1, Electrotypers 2.2, telegraph operator 2.2, actors 1.9, chemists 1.8, Inventors 1.8, photographers and physicians 2.1, technical engineers 1.9, veterinarians 2.2.

I don’t know what paper hangers do, but the Mirror said they were among the least likely to be married, and in 1920, they had an average of 3.1 children–above average.

What about athletes? How smart are they?

Athletes Show Huge Gaps on SAT Scores” is not a promising title for the “nerds are athletic” crew.

The Journal-Constitution studied 54 public universities, “including the members of the six major Bowl Championship Series conferences and other schools whose teams finished the 2007-08 season ranked among the football or men’s basketball top 25.”…

  • Football players average 220 points lower on the SAT than their classmates. Men’s basketball was 227 points lower.
  • University of Florida won the prize for biggest gap between football players and the student body, with players scoring 346 points lower than their peers.
  • Georgia Tech had the nation’s best average SAT score for football players, 1028 of a possible 1600, and best average high school GPA, 3.39 of a possible 4.0. But because its student body is apparently very smart, Tech’s football players still scored 315 SAT points lower than their classmates.
  • UCLA, which has won more NCAA championships in all sports than any other school, had the biggest gap between the average SAT scores of athletes in all sports and its overall student body, at 247 points.

From the original article, which no longer seems to be up on the Journal-Constitution website:

All 53 schools for which football SAT scores were available had at least an 88-point gap between team members’ average score and the average for the student body. …

Football players performed 115 points worse on the SAT than male athletes in other sports.

The differences between athletes’ and non-athletes’ SAT scores were less than half as big for women (73 points) as for men (170).

Many schools routinely used a special admissions process to admit athletes who did not meet the normal entrance requirements. … At Georgia, for instance, 73.5 percent of athletes were special admits compared with 6.6 percent of the student body as a whole.

On the other hand, as Discover Magazine discusses in “The Brain: Why Athletes are Geniuses,” athletic tasks–like catching a fly ball or slapping a hockey puck–require exceptionally fast and accurate brain signals to trigger the correct muscle movements.

Ryan Stegal studied the GPAs of highschool student athletes vs. non-athletes and found that the athletes had higher average GPAs than the non-athletes, but he also notes that the athletes were required to meet certain minimum GPA requirements in order to play.

But within athletics, it looks like the smarter athletes perform better than dumber ones, which is why the NFL uses the Wonderlic Intelligence Test:

NFL draft picks have taken the Wonderlic test for years because team owners need to know if their million dollar player has the cognitive skills to be a star on the field.

What does the NFL know about hiring that most companies don’t? They know that regardless of the position, proof of intelligence plays a profound role in the success of every individual on the team. It’s not enough to have physical ability. The coaches understand that players have to be smart and think quickly to succeed on the field, and the closer they are to the ball the smarter they need to be. That’s why, every potential draft pick takes the Wonderlic Personnel Test at the combine to prove he does–or doesn’t—have the brains to win the game. …

The first use of the WPT in the NFL was by Tom Landry of the Dallas Cowboys in the early 70s, who took a scientific approach to finding players. He believed players who could use their minds where it counted had a strategic advantage over the other teams. He was right, and the test has been used at the combine ever since.

For the NFL, years of testing shows that the higher a player scores on the Wonderlic, the more likely he is to be in the starting lineup—for any position. “There is no other reasonable explanation for the difference in test scores between starting players and those that sit on the bench,” Callans says. “Intelligence plays a role in how well they play the game.”

Let’s look at Exercising Intelligence: How Research Shows a Link Between Physical Activity and Smarts:

A large study conducted at the Sahlgrenska Academy and Sahlgrenska University Hospital in Gothenburg, Sweden, reveals that young adults who regularly exercise have higher IQ scores and are more likely to go on to university.

The study was published in the Proceedings of the National Academy of Sciences (PNAS), and involved more than 1.2 million Swedish men. The men were performing military service and were born between the years 1950 and 1976. Both their physical and IQ test scores were reviewed by the research team. …

The researchers also looked at data for twins and determined that primarily environmental factors are responsible for the association between IQ and fitness, and not genetic makeup. “We have also shown that those youngsters who improve their physical fitness between the ages of 15 and 18 increase their cognitive performance.”…

I have seen similar studies before, some involving mice and some, IIRC, the elderly. It appears that exercise is probably good for you.

I have a few more studies I’d like to mention quickly before moving on to discussion.

Here’s Grip Strength and Physical Demand of Previous Occupation in a Well-Functioning Cohort of Chinese Older Adults (h/t prius_1995) found that participants who had previously worked in construction had greater grip strength than former office workers.

Age and Gender-Specific Normative Data of Grip and Pinch Strength in a Healthy Adult Swiss Population (h/t prius_1995).


If the nerds are in the sedentary cohort, then they be just as athletic if not more athletic than all of the other cohorts except the heavy work.

However, in Revised normative values for grip strength with the Jamar dynamometer, the authors found no effect of profession on grip strength.

And Isometric muscle strength and anthropometric characteristics of a Chinese sample (h/t prius_1995).

And Pumpkin Person has an interesting post about brain size vs. body size.


Discussion: Are nerds real?

Overall, it looks like smarter people are more athletic, more athletic people are smarter, smarter athletes are better athletes, and exercise may make you smarter. For most people, the nerd/jock dichotomy is wrong.

However, there is very little overlap at the very highest end of the athletic and intelligence curves–most college (and thus professional) athletes are less intelligent than the average college student, and most college students are less athletic than the average college (and professional) athlete.

Additionally, while people with STEM degrees make excellent spouses (except for mathematicians, apparently,) their reproductive success is below average: they have sex later than their peers and, as far as the data I’ve been able to find shows, have fewer children.

Stephen Hawking

Even if there is a large overlap between smart people and athletes, they are still separate categories selecting for different things: a cripple can still be a genius, but can’t play football; a dumb person can play sports, but not do well at math. Stephen Hawking can barely move, but he’s still one of the smartest people in the world. So the set of all smart people will always include more “stereotypical nerds” than the set of all athletes, and the set of all athletes will always include more “stereotypical jocks” than the set of all smart people.

In my experience, nerds aren’t socially awkward (aside from their shyness around women.) The myth that they are stems from the fact that they have different interests and communicate in a different way than non-nerds. Let nerds talk to other nerds, and they are perfectly normal, communicative, socially functional people. Put them in a room full of non-nerds, and suddenly the nerds are “awkward.”

Unfortunately, the vast majority of people are not nerds, so many nerds have to spend the majority of their time in the company of lots of people who are very different than themselves. By contrast, very few people of normal IQ and interests ever have to spend time surrounded by the very small population of nerds. If you did put them in a room full of nerds, however, you’d find that suddenly they don’t fit in. The perception that nerds are socially awkward is therefore just normie bias.

Why did the nerd/jock dichotomy become so popular in the 70s? Probably in part because science and technology were really taking off as fields normal people could aspire to major in, man had just landed on the moon and the Intel 4004 was released in 1971.  Very few people went to college or were employed in sciences back in 1920; by 1970, colleges were everywhere and science was booming.

And at the same time, colleges and highschools were ramping up their athletics programs. I’d wager that the average school in the 1800s had neither PE nor athletics of any sort. To find those, you’d probably have to attend private academies like Andover or Exeter. By the 70s, though, schools were taking their athletics programs–even athletic recruitment–seriously.

How strong you felt the dichotomy probably depends on the nature of your school. I have attended schools where all of the students were fairly smart and there was no anti-nerd sentiment, and I have attended schools where my classmates were fiercely anti-nerd and made sure I knew it.

But the dichotomy predates the terminology. Take Superman, first 1938. His disguise is a pair of glasses, because no one can believe that the bookish, mild-mannered, Clark Kent is actually the super-strong Superman. Batman is based on the character of El Zorro, created in 1919. Zorro is an effete, weak, foppish nobleman by day and a dashing, sword-fighting hero of the poor by night. Of course these characters are both smart and athletic, but their disguises only work because others do not expect them to be. As fantasies, the characters are powerful because they provide a vehicle for our own desires: for our everyday normal failings to be just a cover for how secretly amazing we are.

But for the most part, most smart people are perfectly fit, healthy, and coordinated–even the ones who like math.


Parsis, Travellers, and Human Niches

Irish Travellers, 1954


Why are there many kinds of plants and animals? Why doesn’t the best out-compete, eat, and destroy the others, rising to be the sole dominant species on Earth?

In ecology, a niche is an organism’s specific place within the environment. Some animals eat plants; some eat dung. Some live in the sea; others in trees. Different plants flower and grow in different seasons; some are pollinated by bees and some by flies. Every species has its specific niche.

The Competitive Exclusion Principle (aka Gause’s Law) states that ‘no two species can occupy the same niche’ (or positively, ‘two species coexisting must have different niches.’) For example, if squirrels and chipmunks both want to nest in the treetops and eat nuts, (and there are limited treetops and nuts,) then over time, whichever species is better at finding nuts and controlling the treetops will dominate the niche and the other, less successful species will have to find a new niche.

If squirrels are dominating the treetops and nuts, this leaves plenty of room for rabbits to eat grass and owls to eat squirrels.

II. So I was reading recently about the Parsis and the Travellers. The Parsis, as we discussed on Monday, are Zoroastrians, originally from Persia (modern-day Iran,) who settled in India about a thousand yeas ago. They’re often referred to as the “Jews of India” because they played a similar role in Indian society to that historically played by Jews in Europe.*

*Yes I know there are actual Jews in India.

The Travellers are an Irish group that’s functionally similar to Gypsies, but in fact genetically Irish:

In 2011 an analysis of DNA from 40 Travellers was undertaken at the Royal College of Surgeons in Dublin and the University of Edinburgh. The study provided evidence that Irish Travellers are a distinct Irish ethnic minority, who separated from the settled Irish community at least 1000 years ago; the claim was made that they are as distinct from the settled community as Icelanders are from Norwegians.[36]

It appears that Ireland did not have enough Gypsies of Indian extraction and so had to invent its own.

And though I originally thought that only in jest, why not? Gypsies occupy a particular niche, and if there are Gypsies around, I doubt anyone else is going to out-compete them for that niche. But if there aren’t any, then surely someone else could.

According to Wikipedia, the Travellers traditionally were tinkers, mended tinware (like pots) and acquiring dead/old horses for slaughter.

The Gypsies appear to have been originally itinerant musicians/entertainers, but have also worked as tinkers, smiths, peddlers, miners, and horse traders (today, car salesmen.)

These are not glorious jobs, but they are jobs, and peripatetic people have done them.

Jews (and Parsis, presumably) also filled a social niche, using their network of family/religious ties to other Jews throughout the diaspora as the basis of a high-trust business/trading network at a time when trade was difficult and routes were dangerous.

On the subject of “Madeburg rights” or law in Eastern Europe, Wikipedia notes:

In medieval Poland, Jews were invited along with German merchants to settle in cities as part of the royal city development policy.

Jews and Germans were sometimes competitors in those cities. Jews lived under privileges that they carefully negotiated with the king or emperor. They were not subject to city jurisdiction. These privileges guaranteed that they could maintain communal autonomy, live according to their laws, and be subjected directly to the royal jurisdiction in matters concerning Jews and Christians. One of the provisions granted to Jews was that a Jew could not be made Gewährsmann, that is, he could not be compelled to tell from whom he acquired any object which had been sold or pledged to him and which was found in his possession. Other provisions frequently mentioned were a permission to sell meat to Christians, or employ Christian servants.

External merchants coming into the city were not allowed to trade on their own, but instead forced to sell the goods they had brought into the city to local traders, if any wished to buy them.

Note that this situation is immensely better if you already know the guy you’re selling to inside the city and he’s not inclined to cheat you because you both come from the same small, tight-knit group.


Under Bolesław III (1102–1139), the Jews, encouraged by the tolerant regime of this ruler, settled throughout Poland, including over the border in Lithuanian territory as far as Kiev.[32] Bolesław III recognized the utility of Jews in the development of the commercial interests of his country. … Mieszko III employed Jews in his mint as engravers and technical supervisors, and the coins minted during that period even bear Hebraic markings.[30] … Jews enjoyed undisturbed peace and prosperity in the many principalities into which the country was then divided; they formed the middle class in a country where the general population consisted of landlords (developing into szlachta, the unique Polish nobility) and peasants, and they were instrumental in promoting the commercial interests of the land.

If you need merchants and goldsmiths, someone will become merchants and goldsmiths. If it’s useful for those merchants and goldsmiths to all be part of one small, close-knit group, then a small, close-knit group is likely to step into that niche and out-compete anyone else trying to occupy it.

The similarity of the Parsis to the Jews probably has less to do with them both being monotheists (after all, Christians, Muslims, and Sikhs are also monotheists,) and more to do with them both being small but widely-flung diasporic communities united by a common religion that allows them to use their group as a source of trustworthy business partners.

Over hundreds or thousands of years, humans might not just move into social niches, but actually become adapted to them–Jew and Parsis are both reported to be very smart, for example.

III. I can think of several other cases of ethnic groups moving into a particular niche. In the US, the gambling and bootleg alcohol trade were long dominated by ethnic Sicilians, while the crack and heroin trades have been dominated by black and Hispanic gangs.

Note that, while these activities are (often) illegal, they are still things that people want to do and the mafia/gangs are basically providing a goods/services to their customers. As they see it, they’re just businessmen. They’re out to make money, not commit random violence.

That said, these guys do commit lots of violence, including murder, blackmail and extortion. Even violent crime can be its own niche, if it pays well enough.

(Ironically, police crackdown on ethnic Sicilian control in NYC coincided with a massive increase in crime–did the mafia, by controlling a particular territory, keep out competing bands of criminals?)

On a more pleasant note, society is now rich enough that many people can make a living as professional sports stars, marry other professional sports stars, and have children who go on to also be professional sports stars. It’s not quite at the level of “a caste of professional athletes genetically optimized for particular sports,” but if this kept up for a few hundred years, it could be.

Similarly, over in Nepal, “Sherpa” isn’t just a job, it’s an ethnic group. Sherpas, due to their high elevation adaptation, have an advantage over the rest of us when it comes to scaling Mt. Everest, and I hear the global mountain-climbing industry pays them well for their services. A Sherpa who can successfully scale Mt. Everest many times, make lots of money, and raise lots of children in an otherwise impoverished nation is thus a successful Sherpa–and contributing to the group’s further genetic and cultural specialization in the “climbing Mt. Everest” niche.

India, of course, is the ultimate case of ethnic groups specializing into specific jobs–it’d be interesting to see what adaptations different groups have acquired over the years.

I also wonder if the caste system is an effective way to minimize competition between groups in a multi-ethnic society, or if it leads to more resentment and instability in the long run.

Zoroastrian (Parsi) DNA

Farvahar. Persepolis, Iran.

Zoroastrianism is one of the world’s oldest surviving religions and possibly its first monotheistic one. It emerged in now-Iran about 3,000 years ago, but following the Arab (Islamic) conquest of Persia, many Zoroastrians migrated to India, where they became known as the Parsi (from the word for “Persian.”) To be clear, where this post refers to “Parsis” it means the specific Zoroastrian community in India, and where it refers to “Iranian Zoroastrians” it means the Zoroastrians currently living in Iran.

Although Zoroastrianism was once the official state religion of Persia, today only about 190,000 believers remain (according to Wikipedia,) and their numbers are declining.

If you’re thinking that a diasporic community of monotheists sounds familiar, you’re in good company. According to Wikipedia:

Portuguese physician Garcia de Orta observed in 1563 that “there are merchants … in the kingdom of Cambaia … known as Esparcis. We Portuguese call them Jews, but they are not so. They are Gentios.”

Another parallel: Ashkenazi Jews and Parsis are both reported to be very smart. Famous Parsis include Queen Guitarist Freddy Mercury, nuclear physicist Homi J. Bhabha, and our Harvard-employed friend, Homi K. Bhabha.

Lopez et al have recently carried out a very interesting study of Zoroastrian DNA, The Genetic Legacy of Zoroastrianism in Iran and India: Insights into Population Structure, Gene Flow, and Selection:

Historical records indicate that migrants from Persia brought Zoroastrianism to India, but there is debate over the timing of these migrations. Here we present genome-wide autosomal, Y chromosome, and mitochondrial DNA data from Iranian and Indian Zoroastrians and neighboring modern-day Indian and Iranian populations and conduct a comprehensive genome-wide genetic analysis in these groups. … we find that Zoroastrians in Iran and India have increased genetic homogeneity relative to other sampled groups in their respective countries, consistent with their current practices of endogamy. Despite this, we infer that Indian Zoroastrians (Parsis) intermixed with local groups sometime after their arrival in India, dating this mixture to 690–1390 CE and providing strong evidence that Iranian Zoroastrian ancestry was maintained primarily through the male line.

Note that all diasporic–that is, migrant–groups appear to be heavily male. Women tend to stay put while men move and take new wives in their new homelands.

By making use of the rich information in DNA from ancient human remains, we also highlight admixture in the ancestors of Iranian Zoroastrians dated to 570 BCE–746 CE, older than admixture seen in any other sampled Iranian group, consistent with a long-standing isolation of Zoroastrians from outside groups. …

Admixture with whom? (Let’s just read the paper and see if it answers the question):

Furthermore, a recent study using genome-wide autosomal DNA found that haplotype patterns in Iranian Zoroastrians matched more than other modern Iranian groups to a high-coverage early Neolithic farmer genome from Iran

A study of four restriction fragment length polymorphisms (RFLPs) suggested a closer genetic affinity of Parsis to Southern Europeans than to non-Parsis from Bombay. Furthermore, NRY haplotype analysis and patterns of variation at the HLA locus in the Parsis of Pakistan support a predominately Iranian origin. …

In (1) and (2), we detected admixture in the Parsis dated to 27 (range: 17–38) and 32 (19–44) generations ago, respectively, in each case between one predominantly Indian-like source and one predominantly Iranian-like source. This large contribution from an Iranian-like source (∼64%–76%) is not seen in any of our other 7 Indian clusters, though we detect admixture in each of these 7 groups from wide-ranging sources related to modern day individuals from Bangladesh, Cambodia, Europe, Pakistan, or of Jewish heritage (Figures 2 and S7, Tables S5–S7). For Iranian Zoroastrians, we detect admixture only under analysis (2), occurring 66 (42–89) generations ago between a source best genetically explained as a mixture of modern-day Croatian and Cypriot samples, and a second source matching to the Neolithic Iranian farmer WC1. … The two Iranian Zoroastrians that had been excluded as outliers exhibited admixture patterns more similar to the Lebanese, Turkish Jews, or Iranian Bandari individuals than to Zoroastrians (Table S8).

Parsi Wedding, 1905

If I assume a generation is about 25 years long, 27 generations was about 675 years ago; 32 was about 800 years ago. (Though given the wide range on these dates, perhaps we should estimate between 425 and 1,100 years ago.) This sounds consistent with Parsis taking local wives after they arrived in India between the 8th and 10th century CE (after the Arab conquest of Perisa.) Also consistently, this admixture isn’t found in Iranian Zoroastrians.

The Iranians’ admixture occurred about 1,050 and 2,225 years ago, which is an awfully broad time range. Could Croatian or Cypriot migrants have arrived due to the Greek/Roma/ Byzantine Empires? Were they incorporated into the Persian Empire as a result of its territorial conquests or the Arab conquest? Or were they just long-distance merchants who happened to wander into the area?

The Fire Temple of Baku

The authors found that Parsi priests had “the lowest gene diversity values of all population samples studied for both Y and mtDNA,” though they didn’t have enough Iranian Zoroastrian priest samples to compare them to Parsi priests. (I bet this is similar to what you’d find if you sampled Orthodox rabbis.)

Finally, in the genetic selection and diseases section, the authors write:

In the case of the Iranian Zoroastrians, … some of the most significant SNPs… are located upstream of gene SLC39A10 … with an important role in humoral immunity61 or in CALB2 … which plays a major role in the cerebellar physiology.62

With regard to the positive selection tests on Parsis versus India Hindu/Gujarati groups, the most significant SNPs were embedded in WWOX … associated with neurological disorders like early epilepsy … and in a region in chromosome 20 … (see Table S11 for a complete list). …

Genetic isolation and endogamous practices can be associated with higher frequencies of disease prevalence. For example, there are reports claiming a high recurrence of diseases such as diabetes among the Iranian Zoroastrians, and Parkinson, colon cancer, or the deficiency of G6PD, an enzyme that triggers the sudden reduction of red blood cells, among the Parsis.

However, the authors warn that these results are weak (these are rare conditions in an already small population) and cannot not be depended upon.

Navigation and the Wealth of Nations

Global Determinants of Navigational Ability, by Coutrot et al:

Using a mobile-based virtual reality navigation task, we measured spatial navigation ability in more than 2.5 million people globally. Using a clustering approach, we find that navigation ability is not smoothly distributed globally but clustered into five distinct yet geographically related groups of countries. Furthermore, the economic wealth of a nation (Gross Domestic Product per capita) was predictive of the average navigation ability of its inhabitants and gender inequality (Gender Gap Index) was predictive of the size of performance difference between males and females. Thus, cognitive abilities, at least for spatial navigation, are clustered according to economic wealth and gender inequalities globally.

This is an incredible study. They got 2.5 million people from all over the world to participate.

If you’ve been following any of the myriad debates about intelligence, IQ, and education, you’re probably familiar with the concept of “multiple intelligences” and the fact that there’s rather little evidence that people actually have “different intelligences” that operate separately from each other. In general, it looks like people who have brains that are good at working out how to do one kind of task tend to be good at working out other sorts of tasks.

I’ve long held navigational ability as a possible exception to this: perhaps people in, say, Polynesian societies depended historically far more on navigational abilities than the rest of us, even though math and literacy were nearly absent.

Unfortunately, it doesn’t look like the authors got enough samples from Polynesia to include it in the study, but they did get data from Indonesia and the Philippines, which I’ll return to in a moment.

Frankly, I don’t see what the authors mean by “five distinct yet geographically related groups of countries.” South Korea is ranked between the UK and Belgium; Russia is next to Malaysia; Indonesia is next to Portugal and Hungary.

GDP per capita appears to be a stronger predictor than geography:

Some people will say these results merely reflect experience playing video games–people in wealthier countries have probably spent more time and money on computers and games. But assuming that the people who are participating in the study in the first place are people who have access to smartphones, computers, video games, etc., the results are not good for the multiple-intelligences hypothesis.

In the GDP per Capita vs. Conditional Modes (ie how well a nation scored overall, with low scores better than high scores) graph, countries above the trend line are under-performing relative to their GDPs, and countries below the line are over-performing relative to their GDPs.

South Africa, for example, significantly over-performs relative to its GDP, probably due to sampling bias: white South Africans with smartphones and computers were probably more likely to participate in the study than the nation’s 90% black population, but the GDP reflects the entire population. Finland and New Zealand are also under-performing economically, perhaps because Finland is really cold and NZ is isolated.

On the other side of the line, the UAE, Saudi Arabia, and Greece over-perform relative to GDP. Two of these are oil states that would be much poorer if not for geographic chance, and as far as I can tell, the whole Greek economy is being propped up by German loans. (There is also evidence that Greek IQ is falling, though this may be a near universal problem in developed nations.)

Three other nations stand out in the “scoring better than GDP predicts” category: Ukraine, (which suffered under Communism–Communism seems to do bad things to countries,) Indonesia and the Philippines. While we could be looking at selection bias similar to South Africa, these are island nations in which navigational ability surely had some historical effect on people’s ability to survive.

Indonesia and the Philippines still didn’t do as well as first-world nations like Norway and Canada, but they outperformed other nations with similar GDPs like Egypt, India, and Macedonia. This is the best evidence I know of for independent selection for navigational ability in some populations.

The study’s other interesting findings were that women performed consistently worse than men, both across countries and age groups (except for the post-90 cohort, but that might just be an error in the data.) Navigational ability declines steeply for everyone post-23 years old until about 75 years; the authors suggest the subsequent increase in abilities post-70s might be sampling error due to old people who are good at video games being disproportionately likely to seek out video game related challenges.

The authors note that people who drive more (eg, the US and Canada) might do better on navigational tasks than people who use public transportation more (eg, Europeans) but also that Finno-Scandians are among the world’s best navigators despite heavy use of public transport in those countries. The authors write:

We speculate that this specificity may be linked to Nordic countries sharing a culture of participating in a sport related to navigation: orienteering. Invented as an official sport in the late 19th century in Sweden, the first orienteering competition open to the public was held in Norway in 1897. Since then, it has been more popular in Nordic countries than anywhere else in the world, and is taught in many schools [26]. We found that ‘orienteering world championship’ country results significantly correlated with countries’ CM (Pearson’s correlation ρ = .55, p = .01), even after correcting for GDP per capita (see Extended Data Fig. 15). Future targeted research will be required to evaluate the impact of cultural activities on navigation skill.

I suggest a different causal relationship: people make hobbies out of things they’re already good at and enjoy doing, rather than things they’re bad at.



Please note that the study doesn’t look at a big chunk of countries, like most of Africa. Being at the bottom in navigational abilities in this study by no means indicates that a country is at the bottom globally–given the trends already present in the data, it is likely that the poorer countries that weren’t included in the study would do even worse.

Sam Worcester, Cherokee Missionary: Relative or Physiognomy?

Samuel Worcester, 1798-1859

While researching the Trail of Tears and removal of the Five Civilized Tribes from the southeast to Oklahoma, I was brought up short by this photo of Samuel Worcester, of Worcester v. Georgia fame. Sam, born in 1798, was a 7th generation minister and missionary to the Cherokee Indians. When they moved to Oklahoma, he went with them.

And he looks just like my little brother.

My brother who wanted to move to Oklahoma and train to be a missionary. (There’s a relevant school in OK, but it’s expensive.)

If this weren’t a grainy photo from the 1800s, this Sam Worcester could be my long-lost sibling.

I have kin in Oklahoma, though I’m not sure how closely related they are.

But 1798 was a LONG time ago. Depending on exactly when you were born and how quickly your ancestors had their children, you had somewhere around 256 to 512 very-great-grandparents in the late 1700s. A mere 1/256th resemblance is not going to show up like this without constant inter-marriage with other people who also look like your relatives. Of course, Sam and his descendents were in the time and place to do that.

I occasionally see old-stock Americans in the news who are (based on last names) likely 5th or 6th cousins of some branch of the family (including the ones I am related to by law rather than blood) and the resemblances can be uncanny.

(Speaking of family, my brother isn’t the only minister or wanna-be minister in my immediate biological [not adopted] family.)

In Sam Worcester’s case, could the coincidence be physiognomy? Is this just what missionaries look like? Is it time to start believing in reincarnation? Or have I stumbled upon a long-lost relative?

What about you? Have you ever encountered a grainy old photograph that looks just like a loved one?

A little more about Sam:

Worcester was born in Peacham, Vermont on January 19, 1798, to the Rev. Leonard Worcester, a minister. He was the seventh generation of pastors in his family, dating back to ancestors who lived in England. … The young Worcester attended common schools and studied printing with his father.[2] In 1819, he graduated with honors from the University of Vermont.[1]

Samuel Worcester became a Congregational minister and decided to become a missionary. After graduating from Andover Theological Seminary in 1823, he expected to be sent to India, Palestine or the Sandwich Islands. Instead, the American Board of Commissioners for Foreign Missions (ABCFM) sent him to the American Southeast to minister to American Indians.[3]

Worcester married Ann Orr of Bedford, New Hampshire, whom he had met at Andover.[1][2] They moved to Brainerd Mission, where he was assigned as a missionary to the Cherokees in August 1825. The goals ABCFM set for them were, “…make the whole tribe English in their language, civilized in their habits and Christian in their religion.” … Worcester worked with Elias Boudinot to establish the Cherokee Phoenix newspaper, the first among Native American nations.[3]

Ultimately Samuel and Ann had seven children: Ann Eliza, Sarah, Jerusha, Hannah, Leonard, John Orr and Mary Eleanor.[2] Ann Eliza grew up to become a missionary and with her husband, William Schenck Robertson, founded Nuyaka Mission in the Indian Territory.[4]

The westward push of European-American settlers from coastal areas continued to encroach on the Cherokee … With the help of Worcester and his sponsor, the American Board, they made a plan to fight the encroachment by using the courts. They wanted to take a case to the US Supreme Court to define the relationship between the federal and state governments, and establish the sovereignty of the Cherokee nation. No other civil authority would support Cherokee sovereignty to their land and self-government in their territory. Hiring William Wirt, a former U.S. Attorney General, the Cherokee tried to argue their position before the US Supreme Court in Georgia v. Tassel (the court granted a writ of error for a Cherokee convicted in a Georgia court for a murder occurring in Cherokee territory, though the state refused to accept the writ) and Cherokee Nation v. Georgia (1831) (the court dismissed this on technical grounds for lack of jurisdiction).[7] In writing the majority opinion, Chief Justice Marshall described the Cherokee Nation as a “domestic dependent nation” with no rights binding on a state.[1]

Worcester and eleven other missionaries had met at New Echota and published a resolution in protest of an 1830 Georgia law prohibiting all white men from living on Native American land without a state license.[1] While the state law was an effort to restrict white settlement on Cherokee territory, Worcester reasoned that obeying the law would, in effect, be surrendering the sovereignty of the Cherokee Nation to manage their own territory. Once the law had taken effect, Governor George Rockingham Gilmer ordered the militia to arrest Worcester and the others who signed the document and refused to get a license.[7]

After two series of trials, all eleven men were convicted and sentenced to four years of hard labor… Worcester and Elizur Butler declined their pardons, so the Cherokee could take the case to the Supreme Court. … In its late 1832 decision, the Court ruled that the Cherokee Nation was independent and only the federal government had the authority to deal with Indian nations. It vacated the convictions of Worcester and Butler. …

[However] He realized that the larger battle had been lost, because the state and settlers refused to abide by the decision of the Supreme Court. Within three years, the US used its military to force the Cherokee Nation out of the Southeast and on the “Trail of Tears” to lands west of the Mississippi River. …

After being released, Worcester and his wife determined to move their family to Indian Territory to prepare for the coming of the Cherokee under removal. …

His work included setting up the first printing press in that part of the country, translating the Bible and several hymns into Cherokee, and running the mission. In 1839, his wife Ann died; she had been serving as assistant missionary. He remained in Park Hill, where he remarried Erminia Nash in 1842.[1][2]

Worcester worked tirelessly to help resolve the differences between the Georgia Cherokee and the “Old Settlers”, some of whom had relocated there in the late 1820s. On April 20, 1859, he died in Park Hill, Indian Territory.

Aside from being imprisoned, Worcester lost his house when the state of Georgia just up and gave it to someone else in the 1832 Land Lottery and most of his property when a steamer sank on the way to Oklahoma.

I’ve long wondered how (if) the Calvinism of the North ended up in the South. Perhaps Vermont missionaries were part of the process.

Do Black Babies have Blue Eyes?

Short answer: No.

Some of my baby books make claims like, “Babies are born with blue or grey eyes, most of which gradually darken during their first year.” Some go so far as to claim that all babies are born with blue eyes.

This got me curious: what about Black / African American babies? Are they also born with blue/grey eyes which darken with time? Or were my books over-generalizing from a sample population composed primarily of whites?

The idea isn’t totally crazy. After all, I’ve observed plenty of Caucasian children’s eyes go from blue to brown. Pretty much all infants are born with less melanin than their parents, just because fetuses don’t need protection from sunlight.

After much wondering, I remembered that this is the Internet Age and that people post pictures of their babies online and I can just look up pictures of African Newborns and look at their eyes. Here’s a photo of a sweet Uganadan baby with brown eyes; if you scroll down, this article has a photo of a baby boy with black eyes; here’s an African American baby with brown eyes. (I’m just linking because I try not to steal people’s baby photos.)

To be fair, not all of these photos are necessarily of newborns, but could be somewhat older babies, but this is a process that is supposed to happen over the course of several months to a year, not days.

And while some of these infants do have a greyish or bluish tint to their eyes, the overall color is still brown, not blue.

I suppose I should look up photos of Asian babies while we’re at it.


And… they have brown eyes.

There you go, folks. Asian and African babies have brown eyes, not blue.

Let’s Talk Genetics (Polish and German)

source: Big Think: Genetic map of Europe

Continuing with our discussion of German/Polish history/languages/genetics, let’s look at what some actual geneticists have to say.

(If you’re joining us for the first time, the previous two posts summarize to: due to being next door to each other and having been invaded/settled over the millennia by groups which didn’t really care about modern political borders, Polish and German DNA are quite similar. More recent events, however, like Germany invading Poland and trying to kill all of the Poles and ethnic Germans subsequently fleeing/being expelled from Poland at the end of the war have created conditions necessary for genetic differentiation in the two populations.)

So I’ve been looking up whatever papers I can find on the subject.

In Contemporary paternal genetic landscape of Polish and German populations: from early medieval Slavic expansion to post-World War II resettlements, Rebala et al write:

The male genetic landscape of the European continent has been shown to be clinal and influenced primarily by geography rather than by language.1 One of the most outstanding phenomena in the Y-chromosomal diversity in Europe concerns the population of Poland, which reveals geographic homogeneity of Y-chromosomal lineages in spite of a relatively large geographic area seized by the Polish state.2 Moreover, a sharp genetic border has been identified between paternal lineages of neighbouring Poland and Germany, which strictly follows a political border between the two countries.3 Massive human resettlements during and shortly after the World War II (WWII), involving millions of Poles and Germans, have been proposed as an explanation for the observed phenomena.2, 3 Thus, it was possible that the local Polish populations formed after the early Slavic migrations displayed genetic heterogeneity before the war owing to genetic drift and/or gene flow with neighbouring populations. It has been also suggested that the revealed homogeneity of Polish paternal lineages existed already before the war owing to a common genetic substrate inherited from the ancestral Slavic population after the Slavs’ early medieval expansion in Europe.2 …

We used high-resolution typing of Y-chromosomal binary and microsatellite markers first to test for male genetic structure in the Polish population before massive human resettlements in the mid-20th century, and second to verify if the observed present-day genetic differentiation between the Polish and German paternal lineages is a direct consequence of the WWII or it has rather resulted from a genetic barrier between peoples with distinct linguistic backgrounds. The study further focuses on providing an answer to the origin of the expansion of the Slavic language in early medieval Europe. For the purpose of our investigation, we have sampled three pre-WWII Polish regional populations, three modern German populations (including the Slavic-speaking Sorbs) and a modern population of Slovakia. …

AMOVA in the studied populations revealed statistically significant support for two linguistically defined groups of populations in both haplogroup and haplotype distributions (Table 2). It also detected statistically significant genetic differentiation for both haplogroups and haplotypes in three Polish pre-WWII regional populations (Table 2). The AMOVA revealed small but statistically significant genetic differentiation between the Polish pre-war and modern populations (Table 2). When both groups of populations were tested for genetic structure separately, only the modern Polish regional samples showed genetic homogeneity (Table 2). Regional differentiation of 10-STR haplotypes in the pre-WWII populations was retained even if the most linguistically distinct Kashubian speakers were excluded from the analysis (RST=0.00899, P=0.01505; data not shown). Comparison of Y chromosomes associated with etymologically Slavic and German surnames (with frequencies provided in Table 1) did not reveal genetic differentiation within any of the three Polish regional populations for all three (FST, ΦST and RST) genetic distances. Moreover, the German surname-related Y chromosomes were comparably distant from Bavaria and Mecklenburg as the ones associated with the Slavic surnames (Supplementary Figure S2). MDS of pairwise genetic distances showed a clear-cut differentiation between German and Slavic samples (Figure 2). In addition, the MDS analysis revealed the pre-WWII populations from northern, central and southern Poland to be moderately scattered in the plot, on the contrary to modern Polish regional samples, which formed a very tight, homogeneous cluster (Figure 3).

Nicolaus Copernicus, Polish astronomer famous for developing heliocentric model of the solar system

This all seems very reasonable. Modern Poland is probably more homogenous than pre-war Poland in part because modern Poles have cars and trains and can marry people from other parts of Poland much more easily than pre-war Poles could, and possibly because the war itself reduced Polish genetic diversity and displaced much of the population.

Genetic discontinuity along the Polish-German border also makes sense, as national, cultural, and linguistic boundaries all make intermarriage more difficult.

The Discussion portion of this paper is very interesting; I shall quote briefly:

Kayser et al3 revealed significant genetic differentiation between paternal lineages of neighbouring Poland and Germany, which follows a present-day political border and was attributed to massive population movements during and shortly after the WWII. … it remained unknown whether Y-chromosomal diversity in ethnically/linguistically defined Slavic and German populations, which used to be exposed to intensive interethnic contacts and cohabit ethnically mixed territories, was clinal or discontinuous already before the war. In contrast to the regions of Kaszuby and Kociewie, which were politically subordinated to German states for more than three centuries and before the massive human resettlements in the mid-20th century occupied a narrow strip of land between German-speaking territories, the Kurpie region practically never experienced longer periods of German political influence and direct neighbourhood with the German populations. Lusatia was conquered by Germans in the 10th century and since then was a part of German states for most of its history; the modern Lusatians (Sorbs) inhabit a Slavic-speaking island in southeastern Germany. In spite of the fact that these four regions differed significantly in exposure to gene flow with the German population, our results revealed their similar genetic differentiation from Bavaria and Mecklenburg. Moreover, admixture estimates showed hardly detectable German paternal ancestry in Slavs neighbouring German populations for centuries, that is, the Sorbs and Kashubes. However, it should be noted that our regional population samples comprised only individuals of Polish and Sorbian ethnicity and did not involve a pre-WWII German minority of Kaszuby and Kociewie, which owing to forced resettlements in the mid-20th century ceased to exist, and also did not involve Germans constituting since the 19th century a majority ethnic group of Lusatia. Thus, our results concern ethnically/linguistically rather than geographically defined populations and clearly contrast the broad-scale pattern of Y-chromosomal diversity in Europe, which was shown to be strongly driven by geographic proximity rather than by language.1 …

Two main factors are believed to be responsible for the Slavic language extinction in vast territories to the east of the Elbe and Saale rivers: colonisation of the region by the German-speaking settlers, known in historical sources as Ostsiedlung, and assimilation of the local Slavic populations, but contribution of both factors to the formation of a modern eastern German population used to remain highly speculative.8 Previous studies on Y-chromosomal diversity in Germany by Roewer et al17 and Kayser et al3 revealed east–west regional differentiation within the country with eastern German populations clustering between western German and Slavic populations but clearly separated from the latter, which suggested only minor Slavic paternal contribution to the modern eastern Germans. Our ancestry estimates for the Mecklenburg region (Supplementary Table S3) and for the pooled eastern German populations, assessed as being well below 50%, definitely confirm the German colonisation with replacement of autochthonous populations as the main reason for extinction of local Slavic vernaculars. The presented results suggest that early medieval Slavic westward migrations and late medieval and subsequent German eastward migrations, which outnumbered and largely replaced previous populations, as well as very limited male genetic admixture to the neighbouring Slavs (Supplementary Table S4), were likely responsible for the pre-WWII genetic differentiation between Slavic- and German-speaking populations. Woźniak et al18 compared several Slavic populations and did not detect such a sharp genetic boundary in case of Czech and Slovak males with genetically intermediate position between other Slavic and German populations, which was explained by early medieval interactions between Slavic and Germanic tribes on the southern side of the Carpathians. Anyway, paternal lineages from our Slovak population sample were genetically much closer to their Slavic than German counterparts. …

Note that they are discussing paternal ancestry. This does not rule out the possibility of significant Slavic maternal ancestry. Finally:

Our coalescence-based divergence time estimates for the two isolated western Slavic populations almost perfectly match historical and archaeological data on the Slavs’ expansion in Europe in the 5th–6th centuries.4 Several hundred years of demographic expansion before the divergence, as detected by the BATWING, support hypothesis that the early medieval Slavic expansion in Europe was a demographic event rather than solely a linguistic spread of the Slavic language.

Marian Rejewski, Polish mathematician and cryptologist who reconstructed the Nazi German military Enigma cipher machine sight-unseen in 1932

I left out a lot of interesting material, so I recommend reading the complete discussion if you want to know more about Polish/German genetics.

But what about the maternal contribution? Luckily for us, Malyarchuk et al have written Mitochondrial DNA analysis in Poles and Russians:

Mitochondrial DNA (mtDNA) sequence variation was examined in Poles (from the Pomerania-Kujawy region; n = 436) and Russians (from three different regions of the European part of Russia; n = 201)… The classification of mitochondrial haplotypes revealed the presence of all major European haplogroups, which were characterized by similar patterns of distribution in Poles and Russians. An analysis of the distribution of the control region haplotypes did not reveal any specific combinations of unique mtDNA haplotypes and their subclusters that clearly distinguish both Poles and Russians from the neighbouring European populations. The only exception is a novel subcluster U4a within subhaplogroup U4, defined by a diagnostic mutation at nucleotide position 310 in HVS II. This subcluster was found in common predominantly between Poles and Russians (at a frequency of 2.3% and 2.0%, respectively) and may therefore have a central-eastern European origin. …

The analysis of mtDNA haplotype distribution has shown that both Slavonic populations share them mainly with Germans and Finns. The following numbers of the rare shared haplotypes and subclusters were found between populations analyzed: 10% between Poles and Germans, 7.4% between Poles and Russians, and 4.5% between Russians and Germans. A novel subcluster U4-310, defined by mutation at nucleotide position 310 in HVS II, was found predominantly in common between Poles and Russians (at frequency of 2%). Given the relatively high frequency and diversity of this marker among Poles and its low frequency in the neighbouring German and Finnish populations, we suggest a central European origin of U4-310, following by subsequent dispersal of this mtDNA subgroup in eastern European populations during the Slavonic migrations in early Middle Ages.

In other words, for the most part, Poles, Russians, Germans, and even Finns(!) (who do not speak an Indo-European language and are usually genetic outliers in Europe,) all share their maternal DNA.

Migrants, immigrants, and invaders tend disproportionately to be male (just look at any army) while women tend to stay behind. Invading armies might wipe each other out, but the women of a region are typically spared, seen as booty similar to cattle to be distributed among the invaders rather than killed. Female populations therefore tend to be sticky, in a genetic sense, persisting long after all of the men in an area were killed and replaced. The dominant Y-chromosome haplogroup in the area (R1a) hails from the Indo-European invasion (except in Finland, obviously,) but the mtDNA likely predates that expansion.

These data allow us to suggest that Europeans, despite their linguistic differences, originated in the common genetic substratum which predates the formation of the most modern European populations. It seems that considerable genetic similarity between European populations, which has been revealed by mtDNA variation studies, was further accelerated by a process of gene redistribution between populations due to the multiple migrations occurring in Europe during the past milenia…

It is interesting, though, that recent German invasions of Poland left very little in the way of a genetic contribution. I’d wager that WWII was quite a genetic disaster for everyone involved.

If you want more information, Khazaria has a nice list of studies plus short summaries on Polish DNA.