>Thus, on the eve of recorded history, all Europeans now possessed a unique look that would later define them, as if they were a cast of actors being hastily made up and rushed onto stage moments before curtain time.
The key environmental difference between NorthEast Asia and North-Mid Europe is the much stronger cloud coverage in Europe. Some have hypothesized that the small eye openings of modern-day Inuit and Tungusic groups are actually beneficial in the high-glare environments that they inhabit. Also, evidence suggests the east part of the steppe-tundra that started in Europe and went to above Mongolia was inhabited by ANE first, not by the phenotypically East Asian people that today inhabit the top part of eastern and central Siberia.
With that being said, the likely homeland of East Asians, the steppe tundra on the Pacific coast, could've been colder than the other steppe-tundra, as it is actually colder than the livable parts of Scandinavia today. East Asians also have a cold-adapted phenotype, but to a different type of environment than the ones Northern europeans adapted to.
It depends on what you want to explain. Among hunter-gatherers, population density is determined by the availability of food, which is determined, ultimately, by conditions for plant growth (since animals feed on plants or on animals that feed on plants).
Conditions for plant growth are favored primarily by 1) above-zero temperatures and 2) access to water through precipitation or subsurface sources. On both counts, North Asia was less conducive to a substantial human population than Europe.
Some have argued that blue eyes are an adaptation to the misty maritime climate of northwest Europe. But we also see a high prevalence of blue eyes farther east, in areas that have a more continental climate.
Again, we also have to explain the diversification of eye color. If blue eyes are more adaptive than other eye colors, they should have replaced all other eye colors.
I agree the cloud coverage could be a factor, but not the key one. The % of blue eyes in the Baltic and Scandinavian countries ( 80-90%) definitely suggests a strong advantage in those environments, whether that is a better fit environmentally, or different, more self-directed behavioral traits that could be associated with having blue eyes.
What's not being addressed is neoteny. Even anecdotally, when I was a child, my eyes were blue and hair blond, which changed with age to green and brown. I've heard the same from others. We're clearly dealing with persistence of these traits into adulthood.
Most humans have brown eyes and black hair even at birth. So you're arguing that the "new" European hair and eye colors first arose as a neotenous trait and then quickly spread to adults during a relatively short time period. Well, perhaps. But you're proposing a more complicated evolutionary model.
The darkening of hair color with age seems to be a testosterone effect. Consequently, boys darken more than girls as they approach puberty.
Yes, the adult female body seems to mimic certain neotenous traits: a lighter complexion, a smaller nose and chin, smoother, more pliable skin, and a higher vocal pitch. This is what Konrad Lorenz dubbed the Kindchenschema, a set of visual, tactile, and auditory cues that identify a human infant to an adult, who then feels less aggressive and more willing to provide care and nurturance.
The adult female body seems to have adopted these sensorial cues to produce a similar effect on men.
I don't know whether European hair and eye colors are part of the Kindchenschema. Again, most human populations don't have these colors. They seem to be a recent evolutionary development, probably during the last ice age.
I do think you're right that blue eyes are older than the Mesolithic. But, some disagreements:
1. You say that selective effects could have muted the HG signal in northern European EEFs. This is very hard to believe. If EEFs absorbed HG ancestry from HGs that were more similar to EEFs in traits, and if these differences between "farming compatible hunter-gatherers" and "traditionalist hunter gatherers" were so strong that they ended up muting the statistical signal of the introgression (not credible already, because the FSTs between HGs and EEFs were on the order of those between Europeans and Chinese, so any such selective filter would've been overpowered), then wouldn't we expect to see a sharp change of the genetic make-up of the leftover hunter gatherers? But we don't, they are very similar in 2000 BC to what they were in 6000 BC. And besides, you don't need this explanation to posit that N Europeans are mostly HG in descent. Scots, Irishmen, North Germans, Danes, Scandis, Balts – these can all be modelled as three-way mixtures of 45-50% GAC farmer, 45-55% Yamnaya, and 0-10% Baltic or Scandinavian HG. English, Welsh, Germans, Dutch, and north french require a little extra farmer; but not much. GAC were 25% HG themselves – so that's 11-12.5%, in addition to the basically pure HG Yamnaya – so really, up to 75% HG (Balts), without any need for alternative ways of modeling admixture.
2. The population with the highest (known) concentration of blue eyes was the WHGs. But they were not big game hunters, and are not derived from big game hunters. The Gravettians (genotyped as dark, but we can't really know their phenotype), the main big game hunting population of Europe, contributed about a third of the ancestry of the Magdalenians; the Magdalenians in turn contributed 15% AT MOST to the ancestry of the WHGs. The WHGs were derived from a group very close to the Dzudzuana cluster, but without said cluster's Basal introgression. Also, EEFs (~100% Dzudzuana), Natufians (~80% Dz. + 20% Basal or Iberomaurasian) and Iranian HGs all had rare but extant instances of blue eyes. Meanwhile, the population which actually did hunt mammoths, the ANEs, had no known blue eye mutations (I think they might've, but again, we don't know) and only one of the many mutations required for blonde hair. Their descendants, the EHGs, are genotyped as overwhelmingly brown eyed, dark-haired, and olive skinned.
3. There is no evidence that any European population underwent mtDNA bottlenecks beyond what was present in the rest of the world. Haplogroup U shows high internal diversity. There is no evidence that fewer females managed to pass on their genes among Europeans; no evidence that I know of for your theory of low polygyny rates or low male death rates. if there is any genetic or diachronic evidence that there were actually unusual sex ratios among these HG communities, I'd be happy to read it; but it doesn't seem so from looking at the Inuit, the Eskimoes, or the Patagonians (none of whom, I'd add, have been credibly recorded as having blue eyes or blonde hair, although, to be fair, there are some reports of "Copper Inuits" and Blonde Patagonians)
4. Your evidence on novelty effects etc is substantial and convincing. However, I've read elsewhere that blue eyes are actually much more common among men than among women, and that women are more likely to be brown-eyed than men. Also, the appeal of light eyes is far from universal – most cultures outside of Europe consider them a little creepy, and some outright as bad luck.
5. Continuing from point (2), you are correct to say that the people that populate the Baltic and the Scandinavian peninsula – the SHGs and BHGs, who are various mixes of EHG and WHG, with the latter generally higher – are the first population we can securely say had substantial rates of blonde hair + blue eyes. But again – they were not big game hunters, and inherited only ~20% of their ancestry from big game hunters. They were fisher-foragers. Then, the next big expansion of the blue-blond-light skin trifecta was the GAC farmer-pastoralists; they had ~25% ancestry from WHGs and none from mammoth hunting EHGs. The "blonde-ification" Of the IEs after they took over the GAC was probably driven by polygyny – "(not so) gentle men prefer ..."
So, was it sexual selection? Yes, almost certainly, I agree with you on this; but I don't think it was different male-female dynamics specifically. Rather, blue eyes probably emerged among the very earliest west eurasians; thus the G allele in the buran kaya III sample. They then became somewhat more common among the common ancestor of WHGs and Dzudzuana; then became frequent in Europe due to bidirectional sexual AND natural selection affecting both sexes, perhaps a result of a freer, less tradition-bound mating system, with fewer arranged marriages and such. When this happened is anyone's guess; if the Gravettians had these features, they had them through somewhat different genetic paths. So the modern allele package probably became concentrated among the unsampled Epigravettian ancestors of WHGs, maybe in the Italian peninsula c. 23kya.
Blonde hair might've arisen among the ANE, or that might've been among the pre-Dzudzuana population too (I think the latter, since ANFs and Pre-Pottery Neolithic B groups from Israel display it). These were all accelerated through system-wide melanogenesis down-regulation after the Neolithic in cloudy, rainy Northern Europe, and then again reinforced through warrior aristocracies that bred for beauty rather than money.
1. The change in natural selection didn't begin before the hunter-gatherers became farmers. It began when they adopted farming. Those who remained hunter-gathers would have remained unchanged genetically.
The term "farming-compatible hunter-gatherers" seems nonsensical, at least to me. Initially, hunter-gatherers adapted to farming by pushing the envelope of their phenotype.
"not credible already, because the FSTs between HGs and EEFs were on the order of those between Europeans and Chinese"
You're creating a strawman. Demographic replacement of hunter-gatherers by farmers did occur, but it has been over-estimated because of an assumption that all genetic change across the hunter-gatherer/farmer time boundary must be replacement of one population by another. Some of it was. But not all.
"Then wouldn't we expect to see a sharp change of the genetic make-up of the leftover hunter gatherers? " No, we wouldn't. The remaining hunter-gatherers would retain their original genetic profile.
All of the figures you cite are based on the same assumption. It is assumed that only demographic replacement was happening. It is assumed that no genetic changes were caused by a new regime of natural selection. That assumption is not credible.
2. "The population with the highest (known) concentration of blue eyes was the WHGs. " We don't know. In northern and northeast Europe after the last ice age (i.e., after 12,000 years ago), the prevalence was in the range of one half to almost two thirds. This is also the same region where we see the earliest prevalence of non-black hair colors.
"But they were not big game hunters, and are not derived from big game hunters." You're talking about DNA samples that date to well after the ice age. If you go back far enough, the WHGs of post-glacial times were derived from people who were big game hunters during glacial times.
Blue eyes were already prevalent in northern Europe shortly after the end of the ice age. If we want to know how they originated we have to look at earlier samples. All of the samples you cite are from later periods.
3. "There is no evidence that any European population underwent mtDNA bottlenecks beyond what was present in the rest of the world"
I can cites three studies on this point (see below). Proportionately more men have contributed to the gene pool at temperate and Arctic latitudes, as shown by the higher ratio of Y to X chromosome variability among Europeans, Asians, and Amerindians in comparison to long-established tropical populations.
Dupanloup, I., L. Pereira, G. Bertorelle, F. Calafell, M.J. Prata,, A. Amorim, and G. Barbujani. (2003). A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity. Journal of Molecular Evolution 57(1): 85-97. https://doi.org/10.1007/s00239-003-2458-x
Scozzari, R., F. Cruciani, P. Malaspina, P. Santolamazza, B.M. Ciminelli, A. Torroni, et al. (1997). Differential structuring of human populations for homologous X and Y microsatellite loci. American Journal of Human Genetics 61(3): 719-733.
Torroni, A., O. Semino, R. Scozzari, G. Sirugo, G. Spedini, N. Abbas, et al. (1990). Y-chromosome DNA polymorphisms in human populations: Differences between Caucasoids and Africans detected by 49a and 49f probes. Annals of Human Genetics 54(4): 287-296. https://doi.org/10.1111/j.1469-1809.1990.tb00384.x
The sex ratio is highly skewed among present-day Arctic hunter-gatherers, including the Inuit (please see my publications for references).
You ask why we don't see a diversity of hair and eye colors among the Inuit. This is part of the broader question as to why we don't see this evolution in Arctic Asia and Arctic North America. The reason is that these regions were much colder and drier than Europe during the last ice age (because they were further removed from the moderating influence of the Gulf Stream). They thus supported much smaller human populations which frequently died out, especially during the glacial maximum. The effects of sexual selection were thus repeatedly reset to zero.
There is, in fact, evidence of blonde hair evolving independently among some Inuit groups, as you note.
4. "I've read elsewhere that blue eyes are actually much more common among men than among women, and that women are more likely to be brown-eyed than men. "
Not much more. In our Czech study, blue eyes had a prevalence of 33.4% among men and 28% among women. It looks like a certain proportion of blue eyes are expressed as green or hazel eyes among women.
5. "But again – they were not big game hunters, and inherited only ~20% of their ancestry from big game hunters. They were fisher-foragers."
I'm aware they were fisher-foragers -- at the time they left behind their DNA (i.e., the Mesolithic). These DNA samples go back almost to 10,000 years ago, which is not long after the end of the ice age. We don't have earlier samples because the ice age was not conducive to the preservation of hunter-gatherer sites.
My reasoning is simply that the high prevalence of blues shortly after the ice age indicates that blue eyes probably evolved during the ice age.
During the last ice age, there was some fishing along the Atlantic coastline of France. Further north, fishing was impossible because of the icecap over Scandinavia. Gathering was a very marginal source of food because the land was mostly steppe-tundra. For most of Europe, caloric intake came largely from big game, mostly reindeer but also other herbivores.
I have no idea where you found that figure of 20%, since we have limited DNA from Paleolithic hunter groups.
Again, I'm interested in explaining how these new hair and eye colors evolved. If these new colors were already present and highly prevalent shortly after the last ice age, we must look at the conditions that prevailed earlier, rather than later.
You hypothesis seems plausible, but I'm not fully convinced. Then again, I've not heard any hypothesis about the evolution of European hair and eye colors that is fully satisfying to me. I can't help but feel there is something everyone is missing.
Here are a few of my musings based on your article:
1. Attempts to track traits over time using aDNA are fascinating and potentially very informative, but I do worry about sampling biases skewing results. Are some timepoints and locations represented by a variety of skeletons from the same cemeteries, with possibly related individuals? How evenly are different geographic areas represented over time?
2. Based on your hypothesis about arctic conditions causing sexual selection on women, wouldn't you expect the same thing among the Inuit? Why do you think they don't show such eye and hair color diversity? Is the male death rate much lower due to the relative lack of megafauna? Or something else?
3. One possibility I wonder about is pleiotropy. There can be unexpected correlations, like blue-eyed white cats usually being deaf. In humans, apparently having red hair really changes one's sensitivity to pain, to the point of having different anesthesia recommendations for redheads. Could a trait like that be the target of selection, and the hair or eye color is dragged along as a by-product?
4. Are there any informative patterns about pigmentation colors in other species? Lots of huskies have blue eyes, and they are also from the arctic; is there some advantage of this in cold climates (though again, why not the Inuit, I wonder)? Perhaps though you could argue that in huskies it is also evolved due to human preferences, if it was artificially selected.
1. Some of the DNA samples come from the same site (like the Motala site in Sweden). Two individuals were judged to be a single individual because their DNA profiles were identical. I'm aware the aDNA technology has advanced to the point of determining family relationships, but this wasn't done in the studies I consulted. We're still looking at relatively small samples: 39 individuals from Germany (14,000 to 5,200 years ago), 7 individuals from Scandinavia (9,500 to 6,000 years ago) and 9 individuals from the East Baltic (9,500 and 5,360 years ago).
2. This is part of the broader question: "Why did this sexual selection not happen in Arctic Asia and Arctic North America?" The reason is that these regions were much colder and drier than Europe during the last ice age (because they were further removed from the moderating influence of the Gulf Stream). They thus supported much smaller human populations which frequently died out, especially during the glacial maximum. The effects of sexual selection were thus repeatedly reset to zero. In addition, if the population is smaller, you have to wait longer for suitable alleles to appear through mutation.
Blonde hair has been observed in Inuit from Victoria Island. This may have been the beginning of an independent evolution of blonde hair.
3. The "new" hair and eye colors are somewhat sex-linked, i.e., they are more likely to develop if the fetus is exposed to a higher level of estrogen. Red-hair, in particular, seems to be facilitated by estrogen. Consequently, redheads are more likely to develop diseases or syndromes that are estrogen-dependent.
At one point, Greg Cochran was toying with the idea that you propose. In other words, he felt that the hair and eye color polymorphism reflects a behavioral/physiological polymorphism. If you carefully read his book "The 10,000 year explosion," you'll see allusions to that theory.
4. "Human populations and breeds of domestic animals are composed of individuals with a multiplicity of eye (= iris) colorations. Some wild birds and mammals may have intraspecific eye color variability, but this variation seems to be due to the developmental stage of the individual, its breeding status, and/or sexual dimorphism. In other words, eye colour tends to be a species-specific trait in wild animals, and the exceptions are species in which individuals of the same age group or gender all develop the same eye colour. Domestic animals, by definition, include bird and mammal species artificially selected by humans in the last few thousand years. Humans themselves may have acquired a diverse palette of eye colors, likewise in recent evolutionary time, in the Mesolithic or in the Upper Paleolithic.
We posit two previously unrecognized hypotheses regarding eye color variation: 1) eye coloration in wild animals of every species tends to be a fixed trait. 2) Humans and domestic animal populations, on the contrary, have eyes of multiple colors. Sexual selection has been invoked for eye color variation in humans, but this selection mode does not easily apply in domestic animals, where matings are controlled by the human breeder."
Negro, J.J., Carmen Blázquez, M. & Galván, I. Intraspecific eye color variability in birds and mammals: a recent evolutionary event exclusive to humans and domestic animals. Front Zool 14, 53 (2017). https://doi.org/10.1186/s12983-017-0243-8
If I read correctly, there is only one allele for eye color in most of the world but more than a hundred in Europe. Quite apart from the opportunities for sexual selection that this large number of alleles made possible, this suggests (to me at any rate) that there must have been an upstream mutation of some kind unrelated to sexual selection that caused this multiplicity in the first place. Or is there a better explanation?
Mutations require no explanation. They happen all the time in proportion to the size of a population. If there is no selection for them, they will hang around at a low frequency and disappear through stochastic events. There may also be selection to remove atypical "funny-looking" individuals.
I have previously read that blue eyes were favored because they are a recessive trait, and therefore made fathers more certain that their wife's children were also their own. Are you unfamiliar with that idea, or do you find it too implausible to mention?
Yes, I am familiar with that paper. I see two problems with it:
1. Contrary to widespread belief, eye color does not follow a simple two-allele model of inheritance where brown eyes are dominant and blue eyes recessive. A single copy of the blue-eye allele usually produces an intermediate hue, like green or hazel, and even two copies do not always produce blue eyes (Branicki et al. 2009; Eiberg et al. 2008; Martinez-Cadenas et al. 2013). Yes, a blue-eyed man and a blue-eyed woman can have children who are not blue-eyed.
2. The participants were Italian, and there are cultural reasons why some Italian men with blue-eyes tend to prefer blue-eyed women (at least as their stated preference). Such Italian men tend to be from northern Italy and thus associate dark eyes with southern Italians or North African immigrants. Prejudice against both groups does exist and is sufficiently common to explain the findings of this study.
References
Branicki, W., U. Brudnik, and A. Wojas-Pelc. (2009). Interactions between HERC2, OCA2 and MC1R may influence human pigmentation phenotype. Annals of Human Genetics 73(2): 160-170. https://doi.org/10.1111/j.1469-1809.2009.00504.x
Eiberg, H., J. Troelsen, M. Nielsen, A. Mikkelsen, J. Mengel-From, K.W. Kjaer, and L. Hansen. (2008). Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. Human Genetics 123(2): 177-187. http://doi.org/10.1007/s00439-007-0460-x
Martinez-Cadenas, C., M. Pena-Chilet, M. Ibarrola-Villava, and G. Ribas. (2013). Gender is a major factor explaining discrepancies in eye colour prediction based on HERC2/OCA2 genotype and the IrisPlex model. Forensic Science International: Genetics 7(4): 453-460.
>Thus, on the eve of recorded history, all Europeans now possessed a unique look that would later define them, as if they were a cast of actors being hastily made up and rushed onto stage moments before curtain time.
This is so tuff
The key environmental difference between NorthEast Asia and North-Mid Europe is the much stronger cloud coverage in Europe. Some have hypothesized that the small eye openings of modern-day Inuit and Tungusic groups are actually beneficial in the high-glare environments that they inhabit. Also, evidence suggests the east part of the steppe-tundra that started in Europe and went to above Mongolia was inhabited by ANE first, not by the phenotypically East Asian people that today inhabit the top part of eastern and central Siberia.
With that being said, the likely homeland of East Asians, the steppe tundra on the Pacific coast, could've been colder than the other steppe-tundra, as it is actually colder than the livable parts of Scandinavia today. East Asians also have a cold-adapted phenotype, but to a different type of environment than the ones Northern europeans adapted to.
It depends on what you want to explain. Among hunter-gatherers, population density is determined by the availability of food, which is determined, ultimately, by conditions for plant growth (since animals feed on plants or on animals that feed on plants).
Conditions for plant growth are favored primarily by 1) above-zero temperatures and 2) access to water through precipitation or subsurface sources. On both counts, North Asia was less conducive to a substantial human population than Europe.
Some have argued that blue eyes are an adaptation to the misty maritime climate of northwest Europe. But we also see a high prevalence of blue eyes farther east, in areas that have a more continental climate.
Again, we also have to explain the diversification of eye color. If blue eyes are more adaptive than other eye colors, they should have replaced all other eye colors.
I agree the cloud coverage could be a factor, but not the key one. The % of blue eyes in the Baltic and Scandinavian countries ( 80-90%) definitely suggests a strong advantage in those environments, whether that is a better fit environmentally, or different, more self-directed behavioral traits that could be associated with having blue eyes.
The sons of women.
Clearly the other person (linked above - (Piffer, 2025) ) doesn't want to risk it!
"The earliest individual in our dataset carrying the rs12913832 G-allele comes from Buran-Kaya III, a cave site in Crimea (present-day Ukraine)."
https://www.molfar.institute/en/our-influence/projects/lists/foreign-propagandists/
What's not being addressed is neoteny. Even anecdotally, when I was a child, my eyes were blue and hair blond, which changed with age to green and brown. I've heard the same from others. We're clearly dealing with persistence of these traits into adulthood.
Most humans have brown eyes and black hair even at birth. So you're arguing that the "new" European hair and eye colors first arose as a neotenous trait and then quickly spread to adults during a relatively short time period. Well, perhaps. But you're proposing a more complicated evolutionary model.
The darkening of hair color with age seems to be a testosterone effect. Consequently, boys darken more than girls as they approach puberty.
Then perhaps many traits we consider feminine are in fact neoteny and sexes differ in how neotenous they are.
Yes, the adult female body seems to mimic certain neotenous traits: a lighter complexion, a smaller nose and chin, smoother, more pliable skin, and a higher vocal pitch. This is what Konrad Lorenz dubbed the Kindchenschema, a set of visual, tactile, and auditory cues that identify a human infant to an adult, who then feels less aggressive and more willing to provide care and nurturance.
The adult female body seems to have adopted these sensorial cues to produce a similar effect on men.
I don't know whether European hair and eye colors are part of the Kindchenschema. Again, most human populations don't have these colors. They seem to be a recent evolutionary development, probably during the last ice age.
I do think you're right that blue eyes are older than the Mesolithic. But, some disagreements:
1. You say that selective effects could have muted the HG signal in northern European EEFs. This is very hard to believe. If EEFs absorbed HG ancestry from HGs that were more similar to EEFs in traits, and if these differences between "farming compatible hunter-gatherers" and "traditionalist hunter gatherers" were so strong that they ended up muting the statistical signal of the introgression (not credible already, because the FSTs between HGs and EEFs were on the order of those between Europeans and Chinese, so any such selective filter would've been overpowered), then wouldn't we expect to see a sharp change of the genetic make-up of the leftover hunter gatherers? But we don't, they are very similar in 2000 BC to what they were in 6000 BC. And besides, you don't need this explanation to posit that N Europeans are mostly HG in descent. Scots, Irishmen, North Germans, Danes, Scandis, Balts – these can all be modelled as three-way mixtures of 45-50% GAC farmer, 45-55% Yamnaya, and 0-10% Baltic or Scandinavian HG. English, Welsh, Germans, Dutch, and north french require a little extra farmer; but not much. GAC were 25% HG themselves – so that's 11-12.5%, in addition to the basically pure HG Yamnaya – so really, up to 75% HG (Balts), without any need for alternative ways of modeling admixture.
2. The population with the highest (known) concentration of blue eyes was the WHGs. But they were not big game hunters, and are not derived from big game hunters. The Gravettians (genotyped as dark, but we can't really know their phenotype), the main big game hunting population of Europe, contributed about a third of the ancestry of the Magdalenians; the Magdalenians in turn contributed 15% AT MOST to the ancestry of the WHGs. The WHGs were derived from a group very close to the Dzudzuana cluster, but without said cluster's Basal introgression. Also, EEFs (~100% Dzudzuana), Natufians (~80% Dz. + 20% Basal or Iberomaurasian) and Iranian HGs all had rare but extant instances of blue eyes. Meanwhile, the population which actually did hunt mammoths, the ANEs, had no known blue eye mutations (I think they might've, but again, we don't know) and only one of the many mutations required for blonde hair. Their descendants, the EHGs, are genotyped as overwhelmingly brown eyed, dark-haired, and olive skinned.
3. There is no evidence that any European population underwent mtDNA bottlenecks beyond what was present in the rest of the world. Haplogroup U shows high internal diversity. There is no evidence that fewer females managed to pass on their genes among Europeans; no evidence that I know of for your theory of low polygyny rates or low male death rates. if there is any genetic or diachronic evidence that there were actually unusual sex ratios among these HG communities, I'd be happy to read it; but it doesn't seem so from looking at the Inuit, the Eskimoes, or the Patagonians (none of whom, I'd add, have been credibly recorded as having blue eyes or blonde hair, although, to be fair, there are some reports of "Copper Inuits" and Blonde Patagonians)
4. Your evidence on novelty effects etc is substantial and convincing. However, I've read elsewhere that blue eyes are actually much more common among men than among women, and that women are more likely to be brown-eyed than men. Also, the appeal of light eyes is far from universal – most cultures outside of Europe consider them a little creepy, and some outright as bad luck.
5. Continuing from point (2), you are correct to say that the people that populate the Baltic and the Scandinavian peninsula – the SHGs and BHGs, who are various mixes of EHG and WHG, with the latter generally higher – are the first population we can securely say had substantial rates of blonde hair + blue eyes. But again – they were not big game hunters, and inherited only ~20% of their ancestry from big game hunters. They were fisher-foragers. Then, the next big expansion of the blue-blond-light skin trifecta was the GAC farmer-pastoralists; they had ~25% ancestry from WHGs and none from mammoth hunting EHGs. The "blonde-ification" Of the IEs after they took over the GAC was probably driven by polygyny – "(not so) gentle men prefer ..."
So, was it sexual selection? Yes, almost certainly, I agree with you on this; but I don't think it was different male-female dynamics specifically. Rather, blue eyes probably emerged among the very earliest west eurasians; thus the G allele in the buran kaya III sample. They then became somewhat more common among the common ancestor of WHGs and Dzudzuana; then became frequent in Europe due to bidirectional sexual AND natural selection affecting both sexes, perhaps a result of a freer, less tradition-bound mating system, with fewer arranged marriages and such. When this happened is anyone's guess; if the Gravettians had these features, they had them through somewhat different genetic paths. So the modern allele package probably became concentrated among the unsampled Epigravettian ancestors of WHGs, maybe in the Italian peninsula c. 23kya.
Blonde hair might've arisen among the ANE, or that might've been among the pre-Dzudzuana population too (I think the latter, since ANFs and Pre-Pottery Neolithic B groups from Israel display it). These were all accelerated through system-wide melanogenesis down-regulation after the Neolithic in cloudy, rainy Northern Europe, and then again reinforced through warrior aristocracies that bred for beauty rather than money.
1. The change in natural selection didn't begin before the hunter-gatherers became farmers. It began when they adopted farming. Those who remained hunter-gathers would have remained unchanged genetically.
The term "farming-compatible hunter-gatherers" seems nonsensical, at least to me. Initially, hunter-gatherers adapted to farming by pushing the envelope of their phenotype.
"not credible already, because the FSTs between HGs and EEFs were on the order of those between Europeans and Chinese"
You're creating a strawman. Demographic replacement of hunter-gatherers by farmers did occur, but it has been over-estimated because of an assumption that all genetic change across the hunter-gatherer/farmer time boundary must be replacement of one population by another. Some of it was. But not all.
"Then wouldn't we expect to see a sharp change of the genetic make-up of the leftover hunter gatherers? " No, we wouldn't. The remaining hunter-gatherers would retain their original genetic profile.
All of the figures you cite are based on the same assumption. It is assumed that only demographic replacement was happening. It is assumed that no genetic changes were caused by a new regime of natural selection. That assumption is not credible.
2. "The population with the highest (known) concentration of blue eyes was the WHGs. " We don't know. In northern and northeast Europe after the last ice age (i.e., after 12,000 years ago), the prevalence was in the range of one half to almost two thirds. This is also the same region where we see the earliest prevalence of non-black hair colors.
"But they were not big game hunters, and are not derived from big game hunters." You're talking about DNA samples that date to well after the ice age. If you go back far enough, the WHGs of post-glacial times were derived from people who were big game hunters during glacial times.
Blue eyes were already prevalent in northern Europe shortly after the end of the ice age. If we want to know how they originated we have to look at earlier samples. All of the samples you cite are from later periods.
3. "There is no evidence that any European population underwent mtDNA bottlenecks beyond what was present in the rest of the world"
I can cites three studies on this point (see below). Proportionately more men have contributed to the gene pool at temperate and Arctic latitudes, as shown by the higher ratio of Y to X chromosome variability among Europeans, Asians, and Amerindians in comparison to long-established tropical populations.
Dupanloup, I., L. Pereira, G. Bertorelle, F. Calafell, M.J. Prata,, A. Amorim, and G. Barbujani. (2003). A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity. Journal of Molecular Evolution 57(1): 85-97. https://doi.org/10.1007/s00239-003-2458-x
Scozzari, R., F. Cruciani, P. Malaspina, P. Santolamazza, B.M. Ciminelli, A. Torroni, et al. (1997). Differential structuring of human populations for homologous X and Y microsatellite loci. American Journal of Human Genetics 61(3): 719-733.
https://doi.org/10.1086/515500
Torroni, A., O. Semino, R. Scozzari, G. Sirugo, G. Spedini, N. Abbas, et al. (1990). Y-chromosome DNA polymorphisms in human populations: Differences between Caucasoids and Africans detected by 49a and 49f probes. Annals of Human Genetics 54(4): 287-296. https://doi.org/10.1111/j.1469-1809.1990.tb00384.x
The sex ratio is highly skewed among present-day Arctic hunter-gatherers, including the Inuit (please see my publications for references).
You ask why we don't see a diversity of hair and eye colors among the Inuit. This is part of the broader question as to why we don't see this evolution in Arctic Asia and Arctic North America. The reason is that these regions were much colder and drier than Europe during the last ice age (because they were further removed from the moderating influence of the Gulf Stream). They thus supported much smaller human populations which frequently died out, especially during the glacial maximum. The effects of sexual selection were thus repeatedly reset to zero.
There is, in fact, evidence of blonde hair evolving independently among some Inuit groups, as you note.
4. "I've read elsewhere that blue eyes are actually much more common among men than among women, and that women are more likely to be brown-eyed than men. "
Not much more. In our Czech study, blue eyes had a prevalence of 33.4% among men and 28% among women. It looks like a certain proportion of blue eyes are expressed as green or hazel eyes among women.
5. "But again – they were not big game hunters, and inherited only ~20% of their ancestry from big game hunters. They were fisher-foragers."
I'm aware they were fisher-foragers -- at the time they left behind their DNA (i.e., the Mesolithic). These DNA samples go back almost to 10,000 years ago, which is not long after the end of the ice age. We don't have earlier samples because the ice age was not conducive to the preservation of hunter-gatherer sites.
My reasoning is simply that the high prevalence of blues shortly after the ice age indicates that blue eyes probably evolved during the ice age.
During the last ice age, there was some fishing along the Atlantic coastline of France. Further north, fishing was impossible because of the icecap over Scandinavia. Gathering was a very marginal source of food because the land was mostly steppe-tundra. For most of Europe, caloric intake came largely from big game, mostly reindeer but also other herbivores.
I have no idea where you found that figure of 20%, since we have limited DNA from Paleolithic hunter groups.
Again, I'm interested in explaining how these new hair and eye colors evolved. If these new colors were already present and highly prevalent shortly after the last ice age, we must look at the conditions that prevailed earlier, rather than later.
You hypothesis seems plausible, but I'm not fully convinced. Then again, I've not heard any hypothesis about the evolution of European hair and eye colors that is fully satisfying to me. I can't help but feel there is something everyone is missing.
Here are a few of my musings based on your article:
1. Attempts to track traits over time using aDNA are fascinating and potentially very informative, but I do worry about sampling biases skewing results. Are some timepoints and locations represented by a variety of skeletons from the same cemeteries, with possibly related individuals? How evenly are different geographic areas represented over time?
2. Based on your hypothesis about arctic conditions causing sexual selection on women, wouldn't you expect the same thing among the Inuit? Why do you think they don't show such eye and hair color diversity? Is the male death rate much lower due to the relative lack of megafauna? Or something else?
3. One possibility I wonder about is pleiotropy. There can be unexpected correlations, like blue-eyed white cats usually being deaf. In humans, apparently having red hair really changes one's sensitivity to pain, to the point of having different anesthesia recommendations for redheads. Could a trait like that be the target of selection, and the hair or eye color is dragged along as a by-product?
4. Are there any informative patterns about pigmentation colors in other species? Lots of huskies have blue eyes, and they are also from the arctic; is there some advantage of this in cold climates (though again, why not the Inuit, I wonder)? Perhaps though you could argue that in huskies it is also evolved due to human preferences, if it was artificially selected.
1. Some of the DNA samples come from the same site (like the Motala site in Sweden). Two individuals were judged to be a single individual because their DNA profiles were identical. I'm aware the aDNA technology has advanced to the point of determining family relationships, but this wasn't done in the studies I consulted. We're still looking at relatively small samples: 39 individuals from Germany (14,000 to 5,200 years ago), 7 individuals from Scandinavia (9,500 to 6,000 years ago) and 9 individuals from the East Baltic (9,500 and 5,360 years ago).
2. This is part of the broader question: "Why did this sexual selection not happen in Arctic Asia and Arctic North America?" The reason is that these regions were much colder and drier than Europe during the last ice age (because they were further removed from the moderating influence of the Gulf Stream). They thus supported much smaller human populations which frequently died out, especially during the glacial maximum. The effects of sexual selection were thus repeatedly reset to zero. In addition, if the population is smaller, you have to wait longer for suitable alleles to appear through mutation.
Blonde hair has been observed in Inuit from Victoria Island. This may have been the beginning of an independent evolution of blonde hair.
https://evoandproud.blogspot.com/2009/01/blond-inuit.html
3. The "new" hair and eye colors are somewhat sex-linked, i.e., they are more likely to develop if the fetus is exposed to a higher level of estrogen. Red-hair, in particular, seems to be facilitated by estrogen. Consequently, redheads are more likely to develop diseases or syndromes that are estrogen-dependent.
At one point, Greg Cochran was toying with the idea that you propose. In other words, he felt that the hair and eye color polymorphism reflects a behavioral/physiological polymorphism. If you carefully read his book "The 10,000 year explosion," you'll see allusions to that theory.
4. "Human populations and breeds of domestic animals are composed of individuals with a multiplicity of eye (= iris) colorations. Some wild birds and mammals may have intraspecific eye color variability, but this variation seems to be due to the developmental stage of the individual, its breeding status, and/or sexual dimorphism. In other words, eye colour tends to be a species-specific trait in wild animals, and the exceptions are species in which individuals of the same age group or gender all develop the same eye colour. Domestic animals, by definition, include bird and mammal species artificially selected by humans in the last few thousand years. Humans themselves may have acquired a diverse palette of eye colors, likewise in recent evolutionary time, in the Mesolithic or in the Upper Paleolithic.
We posit two previously unrecognized hypotheses regarding eye color variation: 1) eye coloration in wild animals of every species tends to be a fixed trait. 2) Humans and domestic animal populations, on the contrary, have eyes of multiple colors. Sexual selection has been invoked for eye color variation in humans, but this selection mode does not easily apply in domestic animals, where matings are controlled by the human breeder."
Negro, J.J., Carmen Blázquez, M. & Galván, I. Intraspecific eye color variability in birds and mammals: a recent evolutionary event exclusive to humans and domestic animals. Front Zool 14, 53 (2017). https://doi.org/10.1186/s12983-017-0243-8
If I read correctly, there is only one allele for eye color in most of the world but more than a hundred in Europe. Quite apart from the opportunities for sexual selection that this large number of alleles made possible, this suggests (to me at any rate) that there must have been an upstream mutation of some kind unrelated to sexual selection that caused this multiplicity in the first place. Or is there a better explanation?
Mutations require no explanation. They happen all the time in proportion to the size of a population. If there is no selection for them, they will hang around at a low frequency and disappear through stochastic events. There may also be selection to remove atypical "funny-looking" individuals.
I have previously read that blue eyes were favored because they are a recessive trait, and therefore made fathers more certain that their wife's children were also their own. Are you unfamiliar with that idea, or do you find it too implausible to mention?
Yes, I am familiar with that paper. I see two problems with it:
1. Contrary to widespread belief, eye color does not follow a simple two-allele model of inheritance where brown eyes are dominant and blue eyes recessive. A single copy of the blue-eye allele usually produces an intermediate hue, like green or hazel, and even two copies do not always produce blue eyes (Branicki et al. 2009; Eiberg et al. 2008; Martinez-Cadenas et al. 2013). Yes, a blue-eyed man and a blue-eyed woman can have children who are not blue-eyed.
2. The participants were Italian, and there are cultural reasons why some Italian men with blue-eyes tend to prefer blue-eyed women (at least as their stated preference). Such Italian men tend to be from northern Italy and thus associate dark eyes with southern Italians or North African immigrants. Prejudice against both groups does exist and is sufficiently common to explain the findings of this study.
References
Branicki, W., U. Brudnik, and A. Wojas-Pelc. (2009). Interactions between HERC2, OCA2 and MC1R may influence human pigmentation phenotype. Annals of Human Genetics 73(2): 160-170. https://doi.org/10.1111/j.1469-1809.2009.00504.x
Eiberg, H., J. Troelsen, M. Nielsen, A. Mikkelsen, J. Mengel-From, K.W. Kjaer, and L. Hansen. (2008). Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. Human Genetics 123(2): 177-187. http://doi.org/10.1007/s00439-007-0460-x
Martinez-Cadenas, C., M. Pena-Chilet, M. Ibarrola-Villava, and G. Ribas. (2013). Gender is a major factor explaining discrepancies in eye colour prediction based on HERC2/OCA2 genotype and the IrisPlex model. Forensic Science International: Genetics 7(4): 453-460.
https://doi.org/10.1016/j.fsigen.2013.03.007