Disclaimer: I am not a geneticist. For those of you who are new here, this is basically a genetics fan blog. I am trying to learn about genetics, and you know what?
Genetics is complicated.
I fully admit that here’s a lot of stuff that I don’t know yet, nor fully understand.
Luckily for me, there are a few genetics basics that are easy enough to understand that even a middle school student can master them:
“Evolution” is the theory that species change over time due to some individuals within them being better at getting food, reproducing, etc., than other individuals, and thereby passing on their superior traits to their children.
“Genes,” (or “DNA,”) are the biological code for all life, and the physical mechanism by which traits are passed down from parent to child.
“Mendel squares” work for modeling the inheritance of simple traits
More complicated trait are modeled with more complicated math
Lamarckism doesn’t work.
Lamarck was a naturalist who, in the days before genes were discovered, theorized that creatures could pass on “acquired” characteristics. For example, an animal with a relatively normal neck in an area with tall trees might stretch its neck in order to reach the tastiest leaves, and then pass on this longer-neck to its children, who would also stretch their necks and then pass on the trait to their children, until you get giraffes.
A fellow with similar ideas, Lysenko, was a Soviet Scientist who thought he could make strains of cold-tolerant wheat simply by exposing wheat kernels to the cold.
We have the luxury of thinking that Lysenko’s ideas sound silly. The Soviet peasants had to actually try to grow his wheat, and scientists who pointed out that this was nonsense got sent to the gulag.
The problem with Lamarckism is that it doesn’t work. You can’t make wheat grow in Antarctica by sticking it in your freezer for a few months and animals don’t have taller babies just because you stretch their necks.
Pop science articles talk about epigenetics as if it were Lamarckism. Through the magic of epigenetic markers, acquired traits can supposedly be passed down to one’s children and grandchildren, infinitely.
Actual epigenetics, as scientists actually study it, is a real and interesting field. But the effects of epigenetic changes are not so large and permanent as to substantially change most of the way we model genetic inheritance.
Why?
Epigenetics is, in essence, part of how you learn. Suppose you play a disturbing noise every time a mouse smells cherries. Pretty soon, the mouse would learn to associate “fear” and “cherry smell,” and according to Wikipedia, this gets encoded at the epigenetic level. Great, the mouse has learned to be afraid of cherries.
If these epigenetic traits get passed on to the mouse’s children–I am not convinced this is possible but let’s assume it is–then those children can inherit their mother’s fear of cherries.
This is pretty neat, but people take it too far when they assume that as a result, the mouse’s fear will persist over many generations, and that you have essentially just bred a new, cherry-fearing strain of mice.
You, see, you learn new things all the time. So do mice. Your epigenetics therefore keep changing throughout your life. The older you are, the more your epigenetics have changed since you were born. This is why even identical twins differ in small ways from each other. Sooner or later, the young mice will figure out that there isn’t actually any reason to be afraid of cherries, and they’ll stop being afraid.
If people were actually the multi-generational heirs of their ancestors’ trauma, pretty much everyone in the world would be affected, because we all have at least one ancestor who endured some kind of horrors in their life. The entire continent of Europe should be a PTSD basket case due to WWI, WWII, and the Depression.
Thankfully, this is not what we see.
Epigenetics has some real and very interesting effects, but it’s not Lamarckism 2.0.
Basically: Everyone outside of Africa has some Neanderthal DNA. It looks like the ancestors of the Melanesians interbred once with Neanderthals; the ancestors of Europeans interbred twice; the ancestors of Asians interbred three times.
Small amounts of Neanderthal DNA also show up in Africa, probably due to back-migration of people from Eurasia.
Denisovan DNA shows up mainly in Melanesians, but I think there is also a very small amount that shows up in south east Asia, some (or something similar) in Tibetans, and possibly a small amount in the Brazilian rainforest.
Now some kind of other archaic DNA has been detected in the Hazda, Sandawe, and Pygmies of Africa.
Since “Do Native Americans have Neanderthal DNA?” (or something similar) is the most popular search that leads people to my blog, I have begun to suspect that a clarification is in order.
Native Americans (Indians) are not Neanderthals. They are not half or quarter or otherwise significantly Neanderthal. If they were, they would have very noticeable fertility problems in mixed-race relationships.
They may have slightly higher than average Neanderthal admixture than other groups, but that is extremely speculative I don’t know of any scientists who have said so. We’re talking here about quite small amounts, like 0.5%, most of which appears to code for things like immune response and possibly some adaptations for handling long, cold winters. None of this appears to code for physical traits like skull shape, which have been under different selective pressures over the past 40,000 years.
As much as I would love to discover a group with significant Neanderthal DNA, that’s just not something we’ve found in anyone alive today.
WARNING: This post is full of speculations that I am recording for my own sake but are highly likely to be wrong!
From Haak et al.
Hey, did you know that this isn’t actually Haak et al’s full DNA graph? The actual full dataset looks like this:
Isn’t it beautiful?
You’re going to have to click for the full size–sorry I couldn’t fit it all into one screen cap. I’m also sorry that the resolution is poor, and therefore you can’t read the labels (though you should be able to figure out which is which if you just compare with the smaller graphic at the top of the screen. (Supposedly there’s a higher resolution version of this out there, but I couldn’t find it.)
Why the reliance on a greatly cropped image? Just the obvious: the big one is unwieldy, and most of the data people are interested in is at the top.
But the data at the bottom is interesting, too.
On the lefthand side of the graph, we have a measure of granularity–how much fine detail we are getting with our genetic data. The bottom row, therefore, shows us the largest genetic splits between groups–presumably, the oldest splits.
From left to right, we have selections of different ethnic groups’ DNA. Old European skeletons constitute the first group; the mostly pink with some brown section is Native North/South American; the blue and green section is African; the big wide orange section is mostly European and Middle Eastern; then we have some kind of random groups like the Inuit (gold), Onge (pink, Indian Ocean), and Australian Aborigines; the heavily green areas are India; the mixed-up area splitting the green is Eurasian steppe; the yellow area is East Asian; and the final section is Siberian.
Level One: Sub-Saharan Africa (SSA) vs. Non-Sub-Saharan Africa
The bottom row shows us, presumably, the oldest split, between the orange and the blue. All of these light blue groups, from the Ju Hoan (Bushmen/San) to the Yoruba (Nigeria,) Somalis to Hadza (Tanzania,) African Americans to Shua (Khoe speakers of Namibia/Botswana,) are from Africa–sub-Saharan Africa, I’d wager (though I’m not sure whether Ethiopia and Somalia are considered “sub-Saharan.”)
All of the other groups–including the sampled north-African groups like Saharawari (from Western Sahara,) Tunisians, Algerians, Mozabites (Algeria,) and Egyptians–show up in orange.
(Note: Light green and orange are completely arbitrary color choices used to represent the DNA in these graphs; there is nothing inherently “orange” or “green” or any other color about DNA.)
I would not actually have predicted this–other studies I have read predicted that the split between the Bushmen, Pygmies, and other groups in Africa went back further in Africa than the split between Africans and non-Africans, but perhaps the Sahara has been the most significant barrier in human history.
Interestingly, the split is not absolute–there are Sub-Saharan groups with non-SSA admixture, and non-SSA groups with SSA admixture. In fact, most of the SSA groups sampled appear to have some non-SSA admixture, which probably has something to do with back-migration over the centuries; predictably, this is highest in places like Somalia and Ethiopia, fairly high along the east coast of Africa (which has historically been linked via monsoon trade routes to other, non-African countries;) and in African Americans (whose admixture is much more recent.) (Likewise, the admixture found in some of the hunter-gatherer peoples of southern Africa could be relatively recent.)
The Non-SSA groups with the most SSA admixture, are north African groups like the aforementioned Algerians and Tunisians; Middle Eastern groups like the Druze, Syrians, Bedouins, Jordanians, etc.; “Mediterranean” groups like the Sicilians and Maltese; various Jewish groups that live in these areas; and a tiny bit that shows up in the people of the Andaman Islands, Australia, and PNG.
(Oh, and in various old European skeletons.)
Level Two: “Western” vs. “Eastern”
Moving on to level two, we have the next big split, between “Easterners” (mostly Asians) and “Westerners” (mostly Europeans and Middle-Easterners.)
Natives of North/South America, Inuits, Andaman Islanders, Australian Aborigines, Papuans, the Kharia (an Indian tribe that has historically spoken a non-Indo-European language,) some central or northern Asian steppe peoples like the Evens (Siberians,) and of course everyone from the Kusunda (Nepal) through China and Japan and up through, well, more Siberians like the Yakuts, all show up as mostly yellow.
Everyone from Europe, the Middle East, the Caucuses, and all of the sampled Indian populations except the Kharia have orange.
A bunch of little groups from the middle of Eurasia show up as about half-and-half.
Interestingly, some of the older European hunter-gatherer skeletons have small quantities of “Eastern” DNA; this may not represent admixture so much as common ancestry. It also shows up, predictably, in Turkey and the Caucuses; in Russia/Finns; tiny quantities in places like the Ukraine; and quite significantly in India.
Significant “Western” admixture shows up in various Natives North/South Americans (probably due to recent admixture,) the Andaman Islands, Aborigines, PNG, (this may represent something to do with a common ancestor rather than admixture, per se,) and Siberia.
Level Three: Native North/South Americans vs. “Easterners”
At this point, the “light pink” shows up in all of the sampled indigenous tribes of North and South America. A fair amount of it also shows up in the Inuit, and a small quantity in various Siberian tribes. A tiny quantity also show up in some of the older European skeletons (I suspect this is due to older skeletons being more similar to the common ancestors before the splits than trans-Atlantic contact in the stone age, but it could also be due to a small Siberian component having made its way into Europe.)
Even at this level, there is a big difference evident between the groups from Central and South America (almost pure pink) and those from northern North America, (significant chunk of orange.) Some (or all) of that may be due to recent admixture due to adoption of and intermarrying with whites, but some could also be due to the ancestors of the Chipewyans etc. having started out with more, due to sharing ancestors from a more recent migration across the Bering Strait. I’m speculating, of course.
Level Four: Intra-African splits
I don’t know my African ethnic groups like I ought to, but basically we have the Bushmen (aka San,) and I think some Khoe / Khoi peoples in green, with a fair amount of green also showing up in the Pygmies and other hunter-gatherers like the Hadza, plus little bits showing up in groups like the Sandawe and South African Bantus.
Level Five: Australian Aborigines, PNG, and Andamanese split off.
Some of this DNA is shared with folks in India; a tiny bit shows up in central Asia and even east Asia.
Level Six: Red shows up.
This reddish DNA is found in all “Siberian” peoples, people who might have moved recently through Siberia, and people who might be related to or had contact with them. It’s found throughout East Asia, eg, Japan and China, but only found in high quantities among the Inuit and various Siberian groups. At this resolution, oddly, no one–except almost the Itelmen and Koryak–is pure reddish, but at higher resolutions the Nganasan are, while the Itelmen and Koryak aren’t.
Level Seven: The “Indos” of the Indo-Europeans show up
Although no pure light green people have yet been found, their DNA shows up everywhere the Indo-Europeans (aka Yamnaya) went, with their highest concentration in India. Perhaps the light green people got their start in India, and later a group of them merged with the dark blue people to become the Yamnaya, a group of whom then migrated back into India, leaving India with a particularly high % of light green DNA even before the dark blue shows up.
Interestingly, some of this light green also show up in the Andamanese.
Level Eight: The “Europeans” of the Indo-Europeans show up
The dark blue color originates, in the left-hand side of the graph, with a several-thousand years old population of European hunter-gatherers which, as you can see in the slightly younger populations on the far left, nearly got wiped out by a nearly pure orange population of farmers that migrated into Europe from the Middle East. This dark blue population managed to survive out on the Eurasian Steppe, which wasn’t so suited to farming, where it merged with the light-green people. They became the Yamnaya aka the Indo-Europeans. They then spread back into Europe, the Middle East, India, central Asia, and Siberia. (The dark blue in modern Native American populations is probably due to recent admixture.)
Level Nine: The Hadza
The Hadza (a hunter-gatherer people of Tanzania) now show up as bright pink. No one else has a lot of bright pink, but the Pygmies (Mbutu and Biaka,) as well as a variety of other eastern-African groups located near them, like the Luo, Masai, and the Somalis have small amounts.
Level Ten: The Onge (Andamanese)
Not much happens here, but the Onge (from the Andaman Islands) turn peach and stay that way. It looks like a small amount of peach DNA may also be found across part of India (southern India, I’m assuming.)
The Chipewyans turn brown; brown is also found in small quantities in Central America, in moderate quantities in eastern North America, and in the Eskimo/Inuit.
Level Twelve: Pygmies
The Biaka and Mbuti Pygmies differentiate from their neighbors. Tiny quantities of Pygmy DNA found in probably-nearby peoples.
Level Thirteen: Inuit/Eskimo
They become distinctly differentiated from other North American or Siberian tribes (olive green.), Their olive green shade is found in small quantities in some Siberian tribes, but interestingly, appears to be totally absent from other Native American tribes.
Level Fourteen: Horn of Africa
A dusty peach tone is used for groups in the Horn of Africa like the Somalis and Ethiopians, as well as nearby groups like the Dinka. Small amounts of dusty peach are are also found along the East Africa, North Africa, and the Middle East. Smaller amounts appear to be in a variety of other groups related to the Bushmen.
Level Fifteen: The light green turns teal
All of the light green in Europe turns teal, but much of the light green in India stays light green. (Teal also shows up in India.) I have no idea why, other than my aforementioned theory that India had more light green to start with.
Level Sixteen: Amazon Rainforest tribes
The Kuritiana and Suri show up in light olive; light olive is also found in small quantities in other parts of Central and South America, and tiny bits in parts of North America, and maybe tiny amounts in the Eskimo but I don’t see any in the Chukchi, Itelmen, etc.
Level Seventeen: Bedouins
The Bedouins turn light purple; this DNA is also found through out the Middle East, Turkey, North Africa, the Mediterranean (eg Sicily), Greece, Albania, Spain, Bulgaria, Ashkenazim, and a tiny bit In India.
Level Eighteen: Some Bushmen appear to split off from some other Bushmen.
I don’t know much about these groups.
Level Nineteen: Nothing interesting appears to happen.
Please remember that all of this is me speculating. I am definitely not an educated source on these matters, but I hope you’ve had as much fun as I’ve had peering at the DNA and thinking about how people might have moved around and mixed and split to make the colors.
The settlement in Cambridgeshire, which had been buried for 3,000 years, was discovered when the tops of crude protest signs were spotted above layers of mud.
Archaeologist Helen Archer said: “The signs, which include ‘Any old iron? NO THANKS,’ and ‘IRON? IR NO,’ a primitive attempt at wordplay, show that the residents were up in arms about climate-based migration patterns.
Note: The Daily Mash is a humor/satire site, similar to The Onion.
Anyway, on to the genetics!
From Haak et al, rearranged by me
Haak et al. made this graph, but I rearranged it so that the oldest samples are on the left and the newest ones are on the right. When multiple samples were about the same age, I ordered them from west to east (that is, from left to right as you look at a standard map. Unless you are in Australia.) I’ve added the dates (shown as ranges) that were in Haak’s paper. Note the asterisk under Karsdorf–those dates are still uncertain.
The first three genomes are from super old skeletons found out in, like, Russia. I don’t know why they look so crazy–maybe because the DNA is really old and so not very good, or maybe because they actually had a bunch of different DNA in them, or maybe because they’re ancestral to a bunch of different groups. I don’t know! Luckily, it doesn’t really matter for today’s post, so I’ll investigate them later.
Approximately 28,000 years later, we have the Blue People, also known as “Western European Hunter Gatherers,” or WHG. There were people in Europe in intervening 28,000 years; they just aren’t on the table, and I don’t know if anyone has successfully sequenced their genomes yet. (More research required.)
As you might guess, the WHG people hunted and gathered. They had stone tools, and were quite widespread, ranging from Spain (the La Brana1 site,) to Sweden to Samara, Russia (and probably beyond.)
And then some new guys showed up: Farmers.
Known as the Early Eurasian Farmers (EEF,) they first appear on our graph in Starcevo, Serbia, their DNA in orange. They came from the Middle East (the birthplace of agriculture,) bringing their wheat, permanent settlements, and livestock.
Neolithic cultures of Europe–Starcevo is i the lower right-hand corner.
These farmers quickly overran the hunter-gatherers throughout western Europe (though the northern extremes held out longer, most likely due to crops that originated in the Middle East taking a while to adapt to the harsh Scandinavian climate.)
(source: Wikipedia)
The hunter gatherers disappeared (most likely slaughtered by the farmers, but perhaps merely overwhelmed numerically) but their DNA lives on in the descendants of those first farmers. Some groups may have combined willingly–others, as the spoils of war. Within the Farmers’ range, the only place the hunter-gatherers managed to live on appears to be a small island off the coast of Sweden (the second “Skoglund” sample.)
But to the east, out on the Eurasian steppes, the hunter-gatherers lived on. The steppes are known more for their rampaging hordes than their farmers, and this is exactly what they became.
The Yamnaya, as we now call them, are about half WHG and half some new population (I call them the Teal People.) As far as I know, no “pure” teal people have yet been found, but teal DNA is all over the place, from India to Spain.
Teal and blue DNA in India central Asia, and Siberia:
The Yamnaya are also known as the Proto-Indo-Europeans–the guys who spoke the language ancestral to all of today’s Indo-European languages. And like all conquering barbarian hordes, they expanded out of their homeland in present-day southern Russia (north of the Caucuses,) and conquered everything in their path.
Just eyeballing the graph, it looks like the resulting peoples are about half Yamnaya, and about half EEF. This tri-part inheritance is still seen in every European population (and some of their neighbors) today:
If we didn’t have the ancient DNA–or if we had less of it–it would be easy to think that the Blue component in modern Europeans had come directly from the ancient WHG population that lived in their particular area. Instead, much (if not most) of the modern “blue” component hails from the steppes of Russia–a remarkable comeback for the WHGs.
Oh, and the “indigenous” people of Europe? They’re all indigenous to the continent.
Some more helpful graphs, maps, and information:
From Haak et al.From Haak et al.From Haak et al.
On the Iceman, aka Otzi: found in the Alps on the Italian-Austrian border; Same age as Sweden, between 3359 and 3105 BCE. (Hailed from the vicinity of Feldthurns, Italy.)
Analysis of the mtDNA of Ötzi the Iceman, the frozen mummy from 3,300 BC found on the Austrian–Italian border, has shown that Ötzi belongs to the K1 subclade. It cannot be categorized into any of the three modern branches of that subclade (K1a, K1b or K1c). The new subclade has provisionally been named K1ö for Ötzi.[14] Multiplex assay study was able to confirm that the Iceman’s mtDNA belongs to a new European mtDNA clade with a very limited distribution amongst modern data sets.[15]” (source)
Otzi ate grain but was lactose intolerant.
His Y DNA is haplogroup G, which is now rare in Europe:
Various estimated dates and locations have been proposed for the origin of Haplogroup G. The National Geographic Society places haplogroup G origins in the Middle East 30,000 years ago and presumes that people carrying the haplogroup took part in the spread of the Neolithic.[2] Two scholarly papers have also suggested an origin in the Middle East, while differing on the date. …
Haplogroup G2a(SNP P15+) has been identified in neolithic human remains in Europe dating between 5000-3000BC. Furthermore, the majority of all the male skeletons from the European Neolithic period have so far yielded Y-DNA belonging to this haplogroup. The oldest skeletons confirmed by ancient DNA testing as carrying haplogroup G2a were five found in the Avellaner cave burial site for farmers in northeastern Spain and were dated by radiocarbon dating to about 7000 years ago.[5] At the Neolithic cemetery of Derenburg Meerenstieg II, north central Germany, with burial artifacts belonging to the Linear Pottery culture, known in German as Linearbandkeramik (LBK). This skeleton could not be dated by radiocarbon dating, but other skeletons there were dated to between 5,100 and 6,100 years old. The most detailed SNP mutation identified was S126 (L30), which defines G2a3.[6] G2a was found also in 20 out of 22 samples of ancient Y-DNA from Treilles, the type-site of a Late Neolithic group of farmers in the South of France, dated to about 5000 years ago.[7] The fourth site also from the same period is the Ötztal of the Italian Alps where the mummified remains of Ötzi the Iceman were discovered. Preliminary word is that the Iceman belongs to haplogroup G2a2b [8] (earlier called G2a4).
Haplogroup G2a2b is a rare group today in Europe. (source)
… In October 2013, it was reported that 19 modern Tyrolean men were related to Ötzi. Scientists from the Institute of Legal Medicine at Innsbruck Medical University had analysed the DNA of over 3,700 Tyrolean male blood donors and found 19 who shared a particular genetic mutation with the 5,300-year-old man, which led them to identify the link.[46]
The Great Hungarian Plain was a crossroads of cultural transformations that have shaped European prehistory. Here we analyse a 5,000-year transect of human genomes, sampled from petrous bones giving consistently excellent endogenous DNA yields, from 13 Hungarian Neolithic, Copper, Bronze and Iron Age burials including two to high (~22 × ) and seven to ~1 × coverage, to investigate the impact of these on Europe’s genetic landscape. These data suggest genomic shifts with the advent of the Neolithic, Bronze and Iron Ages, with interleaved periods of genome stability. The earliest Neolithic context genome shows a European hunter-gatherer genetic signature and a restricted ancestral population size, suggesting direct contact between cultures after the arrival of the first farmers into Europe. The latest, Iron Age, sample reveals an eastern genomic influence concordant with introduced Steppe burial rites. We observe transition towards lighter pigmentation and surprisingly, no Neolithic presence of lactase persistence.
To investigate European population history around the time of the agricultural transition, we sequenced complete genomes from a ~7,500 year old early farmer from the Linearbandkeramik (LBK) culture from Stuttgart in Germany and an ~8,000 year old hunter-gatherer from the Loschbour rock shelter in Luxembourg. We also generated data from seven ~8,000 year old hunter-gatherers from Motala in Sweden. We compared these genomes and published ancient DNA to new data from 2,196 samples from 185 diverse populations to show that at least three ancestral groups contributed to present-day Europeans. The first are Ancient North Eurasians (ANE), who are more closely related to Upper Paleolithic Siberians than to any present-day population. The second are West European Hunter-Gatherers (WHG), related to the Loschbour individual, who contributed to all Europeans but not to Near Easterners. The third are Early European Farmers (EEF), related to the Stuttgart individual, who were mainly of Near Eastern origin but also harbored WHG-related ancestry. We model the deep relationships of these populations and show that about ~44% of the ancestry of EEF derived from a basal Eurasian lineage that split prior to the separation of other non-Africans.(bold mine.)
Analysis of ancient DNA can reveal historical events that are difficult to discern through study of present-day individuals. To investigate European population history around the time of the agricultural transition, we sequenced complete genomes from a ~7,500 year old early farmer from the Linearbandkeramik (LBK) culture from Stuttgart in Germany and an ~8,000 year old hunter-gatherer from the Loschbour rock shelter in Luxembourg. We also generated data from seven ~8,000 year old hunter-gatherers from Motala in Sweden. We compared these genomes and published ancient DNA to new data from 2,196 samples from 185 diverse populations to show that at least three ancestral groups contributed to present-day Europeans. The first are Ancient North Eurasians (ANE), who are more closely related to Upper Paleolithic Siberians than to any present-day population. The second are West European Hunter-Gatherers (WHG), related to the Loschbour individual, who contributed to all Europeans but not to Near Easterners. The third are Early European Farmers (EEF), related to the Stuttgart individual, who were mainly of Near Eastern origin but also harbored WHG-related ancestry. We model the deep relationships of these populations and show that about ~44% of the ancestry of EEF derived from a basal Eurasian lineage that split prior to the separation of other non-Africans.
To test for human population substructure and to investigate human population history we have analysed Y-chromosome diversity using seven microsatellites (Y-STRs) and ten binary markers (Y-SNPs) in samples from eight regionally distributed populations from Poland (n = 913) and 11 from Germany (n = 1,215). Based on data from both Y-chromosome marker systems, which we found to be highly correlated (r = 0.96), and using spatial analysis of the molecular variance (SAMOVA), we revealed statistically significant support for two groups of populations: (1) all Polish populations and (2) all German populations. … The same population differentiation was detected using Monmonier’s algorithm, with a resulting genetic border between Poland and Germany that closely resembles the course of the political border between both countries. The observed genetic differentiation was mainly, but not exclusively, due to the frequency distribution of two Y-SNP haplogroups and their associated Y-STR haplotypes: R1a1*, most frequent in Poland, and R1*(xR1a1), most frequent in Germany. We suggest here that the pronounced population differentiation between the two geographically neighbouring countries, Poland and Germany, is the consequence of very recent events in human population history, namely the forced human resettlement of many millions of Germans and Poles during and, especially, shortly after World War II. …
British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. … Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. … we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. … Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain.
This is really tentative! And I am not a geneticist, so at this point, I’m just crossing my fingers and hoping I didn’t read any graphs backwards.
Notes:
This map shows Neanderthal DNA admixture in modern human groups (solid color) and Denisovan DNA (polka dots.) The Denisovan estimates are less exact than the Neanderthal estimates. (Also, the guys with Denisovan DNA also have Neanderthal DNA; I just don’t know how much.)
The biggest problem I ran up against was a total lack of numbers. Seriously, everyone likes quoting that “1-4% of non-African DNA is Neanderthal” stat, but no one likes breaking it down by individual country or group.
Some of the sources contradict each other–first we have papers claiming that Europeans have more Neanderthal DNA than Asians, then papers claiming that Asians have more. I went with the Asians have more estimates, since they were more recent. Also, we now think that many African groups also have some Neanderthal DNA, due to more recent back-migration of Eurasians into Africa.
Most of this map is still completely blank, even though I’m sure the data is out there somewhere. I would really appreciate if any of my readers can point me toward a good old list of Neanderthal (or Denisovan) DNA %s by country or group.
Alternatively, if you’ve had your DNA analyzed and know your Neanderthal and/or Denisovan %s, feel free to share in the comments.
Humans–Homo Sapiens or Anatomically Modern Humans–have been around for about 200,000 years. We have only recently–for the past few thousand years or so–begun making a serious effort at recording human history and figuring out what happened before our own times.
Most of what we know about major migrations and changes among human populations come from three major sources: written records, archaeology, and genetics.
Written records are (usually) the easiest to work with. We know when the Spaniards discovered Cuba because we have written records of the event, for example. Unfortunately, written records go back only a few thousand years–covering a teeny portion of human history–and can be highly unreliable. After all, we thought the entire world was only 6 thousand years old for a while because a book that seemed to say so.
Archaeology lets us peer much further back than written records, but with much less detail. We don’t know a lot, for example, about the folks who made Aurignacian tools–what they called themselves, what sort of rituals they had, what they hoped or dreamed of. Without those details, it’s hard to care much about one culture or another. After a while, pots blend into pots, stone tools into stone tools.
Can you tell which one is Aurignacian, and which is Gravettian?
(Oh, I threw in a Mousterian tool, as well. Those were made by Neanderthals, not H. sapiens.)
I can’t, either.
It is difficult to tell whether a change in artifacts between one layer and the next reflects a change in people or a change in technology. The proliferation of steel artifacts in the archaeological record in Mexico circa 1500 reflects an influx of new people, but the proliferation of television sets in the future-archaeological record of my area merely reflects a technological development. Finding a lot of mass graves in an area is, of course, a tip-off that invasion and replacement happened, but invasions aren’t always accompanied by easily identified mass-internments.
This is where genetics comes in. If we can find some skeletons and sequence their DNA, and then find some later or earlier skeletons in the same area and sequence their DNA, then we can get a pretty good idea of whether or not the later people are descended from the earlier people. This probably doesn’t always work (if the people in question are under some kind of selective pressure–which we all are–then their descendants might look genetically different from their ancestors simply due to evolution rather than replacement,) but it is a pretty darn good tool.
As I discussed back in “Oops, Looks Like it was People, not Pots,” archaeologists have fiercely debated over the decades whether the replacement of Narva Pots with Corded Ware Pots circa 3750 ago represented a population replacement or just a change in pot-making preferences:
Luckily for us, genetics has now figured out that the Corded Ware people are actually the Yamnaya, aka the Proto-Indo-Europeans, and that they expanded out of the Eurasian Steppe about 4,000 years ago, replacing much of the native population as they went.
So it’s starting to look like there were quite a few conquering events of this sort.
From, A recent bottleneck of Y chromosome diversity coincides with a global change in culturefrom A Handful of Bronze Age Men Could have fathered two-thirds of Europeans
In general, if you see a lot of mtDNA and only a little Y-DNA, that means there were a lot of women around and only a few men. And that generally means those men just killed all of the other men and raped their wives and children.
Which appears to have happened on a massive scale throughout much of the world around 10,000-4,000 years ago.
Just off the top of my head, recent large-scale migrations and at least partial replacements include the arrival of Indians in Australia around 4,230 years ago; replacement of the Thule people by the Inuit (aka Dorset aka Eskimo) around 1,000 ago; successive waves of steppe peoples like the Turks and Mongols invading their neighbors; the Great Bantu Migration that began about 3,500 years ago; the spread of Polynesians through areas formerly controlled by Melanesians starting around 3,000 BC; displacement of the Ainu by the Japanese over the past couple thousand years; etc.
Replacement of the Thule by the Dorset, from The genetic prehistory of the New World ArcticPaths of the great Bantu MigrationMap is in French. Negative numbers are years BC; positive numbers are years CE.
And of course, we know of many more recent migrations, like the one kicked off by Columbus.
So it looks like people have moved around a lot over the past 10,000 years.
Terms like “bronze age” are a little problematic because people adopted different technologies at different times. So the “bronze age” began around 5,300 years ago in the Middle East, 4,000 years ago in Ireland, and skipped the Inuit entirely (they basically went straight from stone and bone tools to guns.)
Agriculture emerged in the Middle East circa 11,500 years ago; followed by the wheel, 8,500 years ago; carts, 6,500 years ago; and domesticated horses about 6,000 years ago. These technologies made the world ripe for warfare–riders on horseback or in chariots were great at conquering, and agricultural settlements, with their large population centers and piles of food, were great for conquering.
Our conventional views of prehistory are tainted, I suspect, by a mis-perception of time. This is probably basically a quirk of perception–since we remember yesterday better than the day before yesterday, and that day better than last week, and last week better than last year, we tend to think of more recent time periods as longer than they really are, and older time periods as relatively shorter. Children are most prone to this; ask a child to make a numberline showing events like “Last week, my last birthday, the year I was born, and the year mommy was born,” and you’ll tend to get a very distorted number line. Grown ups are much better at this task (we can count the time-distance between these events,) but we’re not perfect.
We show this same tendency when thinking about human history. Our written documents barely go back past 3,000 years, and as far as most people are concerned, this is the beginning of “history”. Nevermind that humans have been around for 200,000 years–that’s 197,000 years of human history that we tend to condense down to: humans evolved, left Africa, and invented agriculture–then came us. We tend to mentally assign approximately equal chunks of time to each phase, which leads to things like people thinking that the Basques–who speak a language isolate–are an ancient, archaic people who hail directly from the first humans, or Neanderthals, or somesuch. Neanderthals disappeared around 40,000 years, and the Indo-European language expansion probably cut the Basques off from their fellow-language speakers about 3,000 years ago. Of course, the Basques could have been cut off since the Neanderthal age, but that’s a jump of 37,000 years (or more) on very little evidence. Likewise, we tend to assume that people just spread out from their original African homeland, got to where they were going, sat down, and never moved again. With the exception of Columbus and his European co-ethnics, everyone is sort of assumed to have gotten where they are now about 100,000-40,000 years ago. (Or the equivalent time period for people who think humanity is much younger or older than it is.)
But the emerging picture is one of conquering–lots of conquering, at least in the time periods we’ve been able to get details on. But go back more than 10,000 years or so, and the records start petering out. We’ve got no writing, far fewer artifacts, and even the DNA breaks down. The technology we’ve developed for extracting and sequencing ancient DNA is amazing, but I suspect we’ll have a devil of a time trying to find any well-preserved 40,000 year old DNA in the rainforest.
So what did the human story look like between 200,000 and 10,000 years ago? Have humans been conquering and re-conquering each other from the beginning? Is it ethnic group after ethnic group, all the way down? Or did lower population density in the pre-agricultural era make it easier to spread out and avoid one’s neighbors than to bother fighting with them? Certainly armies would have spread much less slowly before the domestication of the horse and invention of the chariot. (Not to mention that they require quite a bit of food, which is a tough sort of thing to get in large, easily-transportable form if you’re a hunter-gatherer.)
Certainly prehistoric peoples slaughtered (or slaughter) each other with great frequency–we can tell that:
It doesn’t take a lot of technology to go put a spear into your neighbor’s chest. Even bands of chimps go smash other bands of chimps to bits with rocks.
The authors propose that a genetic component found in Horn of Africa populations back-migrated to Africa from Eurasia ~23 thousand years ago. … For a time, there was a taboo against imagining back-migration into Africa; in a sense this was reasonable on parsimony grounds: Africans have most autosomal genetic diversity and the basal clades of mtDNA and Y-chromosomes; a model with Out-of-Africa is simpler than one with both Out-of and Into-Africa. However, we now know that pretty much all Africans have Eurasian ancestry, ranging from at least traces in theYoruba and Pygmies (to account for the Neandertal admixture) to intermediate values in East Africans, to quite a lot in North Africans.
Eurasian admixture in Africa seems to be general, variable, and to have occurred at different time scales. It’s still the best hypothesis that modern humans originated in Africa initially and migrated into Eurasia. However, it is no longer clear that Africa was always the pump and never the destination of human migrations.
Whether this was “conquering” or just wandering remains to be discovered.
As for me, my money’s on horses and agriculture making warfare and dispersal faster and more efficient, not fundamentally changing our human proclivities toward our neighbors.
Unfortunately, Googling “Why are people Rh-?” leads you down one of those feveredrabbit holesfull of crazy. See, “Rh” was originally named after the rhesus monkey because some early blood work discoveries were done with monkey blood instead of human blood, probably for obvious reasons related to monkeys being more common lab subjects than humans. Rh+/Rh- blood in humans doesn’t actually have anything to do with rhesus monkeys. But some people have interpreted the Rh+/Rh- distinction as meaning that some people have monkey blood and are therefore descended from monkeys, while other people don’t have monkey blood and therefore aren’t descended from monkeys. They think Rh- folks are descended from reptiles or gods or angels or ancient human breeding experiments or something else.
I’ve got news for you. You’re all descended from apes. Yes, even you.
Can someone explain what, exactly, motivates these fever dreams of alien god blood? “Crazy” seems an inadequate answer, because most of these people can type in complete sentences and even form coherent paragraphs, in contrast to, say, schizophrenics, who as far as I know have difficulty with such tasks. Is it just a side effect of being too dumb to tell the difference between “things scientists believe are reasonably plausible” and “a guy claiming that Rh- people are space aliens with extra vertebrae?” Or maybe a critical percent of them are just 15?
Anyway, back on topic, since it seems basically like Rh- people shouldn’t exist, why do they? There are three basic possibilities:
Random chance.
Founder effect in some populations
Some beneficial effect to being Rh- or heterozygous
If random chance were the solution, we’d expect to find Rh- people distributed in roughly equal quantities throughout the world, or much of it. This is not what we find. Rather, according to Wikipedia, Rh- is most common among the Basque people (21-36% of Basques are Rh-); fairly common among other Europeans (16%); rare among African Americans, who have some European admixture, (7%); occurs occasionally in Siberians (% not given); shows up in about 1% of Native Americans; and is almost totally unknown in Africans and “Asians.” (Remember that this only counts people who are homozygous for the negative allele; due to heterozygosity, approximately 10% of Native Americans have the the negative allele. By contrast, only 1% of “Asians” have the allele.)
If you’ve read a lot of my posts, that list should match a pattern you already know; you can see part of it at the top of the screen, but Haak’s data includes more of the relevant Siberian and Native American groups:
From Haak et al.
Click to get a good look. Unfortunately, different people use different colors on their charts, so “blue” or “yellow” don’t necessarily mean the same things on different charts. Luckily for us, the “dark blue” seems to represent the same thing in both charts.
Dark blue is an ancient, ancestral, shall we say indigenous DNA group that’s found in ancient European skeletons from places like Sweden and Hungary, and is found in large chunks in all modern European populations (Gypsies probably excepted.) Dark blue is also found, in smaller amounts, in some north African populations, west Asian (including the Caucasus and northern Middle East but not really the bulk of the Middle East,) India, and Siberia (the relevant groups here are the Chuvash, Mansi, Even, Selkup, Aleut, Tlingit, Yukagir, Tubalar, Altaian, Dolgan, and Yakut). It’s found in tiny bits in Native American DNA, either because Native Americans brought it with them when they crossed the Bering Strait, or because of recent European admixture. (Or both.)
Interestingly, the Basque have very little of the “teal” (light green in the graph at the top of the blog,) simply because teal was brought in with the Indo-European invasion and Basque aren’t Indo-European. Teal is also very common in India (Indo-European and all that,) but Rh- isn’t common in India.
The “orange” DNA (light blue at the top of the blog) is found throughout the Middle East, where Rh- isn’t, and isn’t found much in Siberia, where Rh- is.
In other words, the Dark Blue people left DNA in approximately the right amounts in all of the relevant people, and the other color-groups in the chart didn’t.
In Africa and Asia, it seems likely to me that the Rh- people actually are the result of random chance. But among the folks with Blue People admixture, I suspect that we are looking at a Founder Effect–that is, when the original band of hunter gatherers who became the Blue People split off from the other tribes, they just happened, by random chance, to have a higher than average percentage of people with Rh- alleles than the rest of the human population.
This happens all the time; if you were to just pick ten random people off the street and test their DNA, you’d likely find that your random population has some genes that are far more common or rarer than in humanity as a whole.
But this does not explain the persistence of Rh-, much less its rather high frequency among the Basque.
First, I want to stop and make a PSA about the Basque:
The Basque are not super people who descended directly from the gods, aliens, Neanderthals, the first primeval man, or whatever. They’re just some guys who, like the Sardinians, didn’t get conquered by the Indo-Europeans, and so never picked up an Indo-European language and held onto a slightly different culture, though they’ve had a ton of cultural contact with the Spanish and French over the years and probably all speak Spanish and/or French these days.
Humans–by which I mean “anatomically modern humans” as they are called–have been around for approximately 200,000 years. About 100,000-70,000 years ago, humans left Africa and spread out across the rest of the world. (We picked up our Neanderthal admixture around this time, so pretty much all non-Africans have Neanderthal DNA, and even the Africans probably have some Neanderthal DNA because it looks like some non-Africans later went back to Africa and intermarried with the people there, because humans have moved around a lot over the past 100,000 years.)
Indo-European, as a language family, didn’t get going until about 8,000 to 6,000 years ago. It didn’t reach France until about 3,000 years ago, and got to Spain even later.
In other words, the Basques are not the sole living descendents of the first peoples from 200,000 years ago, or Neanderthals from 40,000 years ago. They are among the few unconquered descendents of people who lived about 3,000 years ago. You know, about the time the Greeks and Romans were getting going, or maybe the Assyrian Empire. Not prehistory.
Back to our story.
Unfortunately, there isn’t a lot of research on why Rh- exists, but some folks have been pursuing the Toxoplasma Gondii angle. Basically, the idea is that if Sickle Cell Anemia exists because heterozygous sickle cell carriers are protected against malaria, even if folks who are homozygous for SSA die off.
Toxoplasma turns out to be one of the most common parasitic infections, infecting 30-50% of humans. I have yet to find what I consider a reliable-looking map of rates of T. gondii infection world-wide, but it infects about 22% of Americans over 12, and infection rates reach 95% in some places. (And 84% in France, probably due to bad hygiene and raw meat consumption.)
Even though T. gondii likes pretty much any warm-blooded host, they can only reproduce in cats/felids. So I wouldn’t expect any T. gondii in areas with no cats, like Australia before the Europeans got there.
The conclusions are kind of mixed, and I put this in the “needs more research” category due to some small Ns, but nevertheless, here’s what they found:
Among uninfected people in an ethnically homogenous population, Rh- males had faster reaction times than Rh+ males. However, when infected, the Rh-s become slower than the Rh+s (who showed very little change). But if we break the Rh+ group into homozygous Rh++ and heterozygous Rh+-s, we see something remarkable: the Rh++s have worse reaction times following infection, but the Rh+-s’ reactions times actually decreased!
The only problem with this theory is that T. gondii has probably historically been most closely associated with parts of the world with more cats, and Africa, the Middle East, and India historically had more cats than Europe, and certainly more than Siberia. If the idea is that being heterozygous is supposed to be protective against T. gondii, we’d expect to see more heterozygotes in areas with high rates of T. gondii, just as Sickle Cell Anemia is common in areas with malaria. We wouldn’t expect it in places like Siberia, where there are very few cats.
But perhaps the answer is more straightforward: Rh++ is protective against T. Gondii, but at the cost of lower reaction times. Rh– confers faster reaction times, but sucks against T. Gondii. Rh-s could therefore have an advantage over Rh++s and proliferate in areas with few cats, like Siberia.
But T gondii has had time to adapt to the older variant (Rh++;) Rh+- confuses it, thus offering protection against slower reaction times mostly by accident rather than positive selection for Rh+- people in areas with high levels of T. gondii.
Of course, this is all speculation; maybe folks in the Basque region have actually just had a lot of housecats and so contacted T. gondii more than other people, or maybe we’re just seeing an “Elderly Hispanic Woman Effect” due to the data being split into a lot of categories.
Things being as they are, I’d suggest studying the Basque and seeing if Basques with Rh- alleles have any traits that Basques with Rh+s don’t.
I really wish there were some more research on this subject! I guess we just don’t know yet.
ETA: I just realized something that, in retrospect, seems really obvious. If the French have an 85% T. Gondii infection rate, then the Basques–whose territory is partly in France and partly in Spain–may also have a very high infection rate. The French must have a ton of cats. Infection rates probably have more to do with the density of domesticated cats than of wild cats; the prevalence of Rh- and Rh+- alleles may have nothing to do with ancient cave people, but be a more recently selected adaptation. I don’t know when cats became common in Europe, but I’m guessing that plague-infested Medieval cities invited a fair number of cats. Hey, better T. Gondii than Yersina Pestis. If the Basques have somewhere near an 85% T. gondii infection rate, and have had it for a while–say, since the Middle Ages–their current high rates of Rh- blood may in fact be due to Rh+- folks being protected against the effects of infection.
I don’t know why I didn’t see that earlier.
Now I want to know whether people with T. Gondii are more likely to go on strike or start revolutions.
People often make the mistake of over-generalizing other people. We speak of “Indians,” “Native Americans,” or better yet, “Indigenous Peoples,” as though one couldn’t tell the difference between a Maori and an Eskimo; as though only two undifferentiated blocks of humanity existed, everywhere on the globe: noble first people who moved into the area thousands upon thousands of years ago, sat down, and never moved again, and evil invaders who showed up yesterday.
In reality, Group A has conquered and replaced Group B and been conquered and replaced in turn by Group C since time immemorial. Sometimes the conquered group gets incorporated into the new group, and years down the line we can still find their DNA in their descendants. At other times, all that’s left is an abrupt transition in the archeological record between one set of artifacts and skull types and another.
Even “Indigenous” peoples have been migrating, conquering and slaughtering each other since time immemorial. The only difference between them and Europeans is that the Europeans did it more recently and while white.
When we take a good look at the Indians’ DNA, we find evidence of multiple invasion waves, some of them genocidal. The Sururi, Pima, and Chippewyans are clearly distinct, as are the Eskimo and Aleuts:
DNA of the Eskimos and related peoplesDNA of the Aleuts and related peoples
Please note that Haak’s chart and the chart I have at the top of the blog use different colors to represent the same things; genetic admixture of course does not have any inherent color, so the choice of colors is entirely up to the person making the graph.)
The Karitiana are one of those mixed horticulturalist/hunter-gatherer tribes from deep in the Amazon Rainforest who have extremely little contact with the outside world and are suspected of having Denisovan DNA and thus being potentially descended from an ancient wave of Melanesians who either got to the Americas first, or else very mysteriously made it to the rainforest without leaving significant genetic traces elsewhere. I’m going with they got here first, because that explanation makes more sense.
The Pima People of southern Arizona had extensive trade and irrigation networks, and are believed to be descended from the Hohokam people, who lived in the same area and also built and maintained irrigation networks and cities, and are probably generally related to the Puebloan Peoples, who also built cities in the South West. An observer wrote about the Puebloans:
When these regions were first discovered it appears that the inhabitants lived in comfortable houses and cultivated the soil, as they have continued to do up to the present time. Indeed, they are now considered the best horticulturists in the country, furnishing most of the fruits and a large portion of the vegetable supplies that are to be found in the markets. They were until very lately the only people in New Mexico who cultivated the grape. They also maintain at the present time considerable herds of cattle, horses, etc. They are, in short, a remarkably sober and industrious race, conspicuous for morality and honesty, and very little given to quarrelling or dissipation … Josiah Gregg, Commerce of the Prairies: or, The journal of a Santa Fé trader, 1831–1839
Linguistically, the Pima speak an Uto-Aztecan language, connecting them with the Soshoni to the north, Hopi to the east, and the Aztecs to the south (and even further south, since the family is also spoken in Equador):
Map of Uto-Aztecan language distribution
The Aztecs, as you probably already know, had a large empire with cities, roads, trade, taxes, etc.
In other words, the Pima were far more technologically advanced than the Karitiana, which suggests that the arrow of conquering here goes from Pima-related people to Karitiana-related people, rather than the other way around.
Now, obviously, the Pima did not travel down to Bolivia, kill a bunch of Karitiana people living in Bolivia, rape their women, and then head back to Arizona. More likely, the ancestors of the Karitiana once lived throughout much of South and Central America, and perhaps even further afield. The ancestors of the Pima then invaded, killing a bunch of the locals and incorporating a few of their women into their tribes. The Karitiana managed to survive in the rainforest due to the rainforest being very difficult to conquer, and the Pima failed to mix with other groups due to being the only guys interested in living in the middle of the Arizona desert.
Those guys in the southern branch of the family are the Navajos and Apache. These languages are speculated to be linked to Siberian languages like the Yeniseian.
The Algonquin people (of whom the Ojibwe are part,) come from the North East US and Canada:
Map of Algonquian Language Family distribution
There also exist a couple of languages on the California coast which appear to be related to the Algonquin Family, possibly a case of Survival on the Fringes as a new wave of invaders migrated from the Bering Strait.
The Algonquins appear to have been semi-nomadic semi-horticulturalists. They grew corn and squash and beans, and also moved around hunting game and gathering wild plants as necessary.
Where we see red admixture in Haak’s graph, that means Siberian people. Where we see dark blue + orange + teal, that’s typical European. Most likely this means that the Algonquins in Haak’s data have some recent European ancestors due to a lot of inter-marriage happening over the past few hundred years in their part of the world. (The Chipewyans live in a much more isolated part of the continent.) However, some of that DNA might also have come with them when they migrated to North America years and yeas ago, due to their ancient Siberian ancestors having merged with an off-shoot of the same groups that modern Europeans are descended from. This is a likely explanation for the Aleuts and Tlingit peoples, whose dark blue and teal patches definitely look similar to those of other Siberian peoples. (Although, interestingly, they lack the red. Maybe the red was a later addition, or just didn’t make it over there in as large quantities.)
The Eskimo I have spoken of before; they appear to have wiped out everyone else in their immediate area. They live around the coastal rim of Alaska and northern Canada.
The Aleuts likely represent some kind of merger between the Eskimo and other Siberian peoples.
My summary interpretation:
Wave One: The Green People. Traces of their DNA appear to be in the Ojibwe, Eskimos, and Chileans, so they may have covered most of North and South America at one time.
Wave Two: The Pink People. They wiped out the vast majority of the Green people throughout North America, but as migration thinned their numbers, they ended up intermarrying instead of killing some of the Greens down in Central and South America.
The Green People only survived in any significant numbers deep in the rainforest, where the Pink People couldn’t reach. These Greens became the Karitiana.
Wave Three: The Brown people. These guys wiped out all of the Pink people in northwest Canada and Alaska, but as migration to the east thinned their numbers, they had to inter-marry with the local Pinks. This mixed group became the Algonquins, while the unmixed Browns became the Chipewyans.
Few Browns managed to push their way south, either because they just haven’t had enough time, or because they aren’t suited to the hotter climate. Either way, most of the Pink People went unconquered to the south, allowing the Pima and their neighbors to flourish.
Wave Four: The Eskimo, who wiped out most of the other people in their area.
Worldwide distribution of B006, (from Yotova et al. “An X-Linked Haplotype of Neandertal Origin Is Present Among All Non-African Populations,” Mol. Biol. Evol. 28 (7), 2011).SNP PCA from Skoglund & Jakobsson’s “Archaic Human Ancestry in East Asia” (2011)
(Please note that Africans do not have chimpanzee admixture, despite the labeling on the graph–no human group has chimp admixture, because chimps and humans have different #s of chromosomes, so even if you could get a successful cross, the resulting child would be infertile, like a mule. I assume the point of the chimp node is just to represent that which has neither Neanderthal nor Denisovan admixture, though of course there is the possibility of some other form of archaic hominin admixture in Africans.)
So, Native Americans appear to have a ton of Neanderthal DNA. (Relatively speaking.)
Possibilities:
It’s all measurement error/convergent evolution/something else other than archaic admixture.
As much as I hate to say it, I still consider this very likely. There is just a ton of stuff that we don’t about the Americas–like how and when people first got here. I’m sticking here with what I think are the most scientifically-supported theories, but a lot of this is still quite disputed. In particular, all of this genetic admixture business is still kind of speculative, and when people start talking about finding admixture in the admixture, either life is totally awesome, or we’re trying too hard.
2. Survival at the Fringes theory
A lot of people seem to look at this data and respond with something like, “But Neanderthals are from Europe, not America!” But this is not a big issue; the Indians are descended from people who passed through Neanderthal-inhabited regions (the Middle East), just like everyone else with Neanderthal DNA. The migration to the Americas took place long after they acquired Neanderthal admixture.
But this doesn’t explain why they have so much of it.
My “concentration on the edge” theory states that when one population is displaced by another population, you end up with a “fringe” of the original population’s traits. Sometimes this fringe results in isolated groups, as the invading population completely surrounds or cuts off a remnant population from their former range.
The Ainu, for example, resemble certain other Oceanin groups, but not their neighbors, the Japanese. I’m speculating here, so don’t take my word for it.
But I have a much better case with the distribution of red hair:
(So far I have found nothing explaining that dot over in Russia.)
Red hair is highly associated with the so-called Celtic fringe. It looks like it’s highly concentrated in Wales, Scotland, and parts of Ireland, but since I know a little history, and I know these aren’t areas of concentration, but just the areas that managed to escape being displaced by Anglo-Saxon invaders, just by virtue of being further away from the south-east coast of Britain.
One can imagine that the isolated dot in the middle of Russia might, at one time, have been connected with the other red-haired regions before other peoples invaded the lands between them and cut them off.
Compare to the map of blond hair:
Blond hair looks like it has been spreading steadily outward from a central source.
So what does this have to do with Neanderthal admixture in Native Americans?
It means that I think the Native Americans may have closer to original levels of Neanderthal admixture, while people in Europe and Asia have lower admixture because they mixed with later waves of people who came from Africa and had no Neanderthal admixture.
3. The Bering Strait selected for Neanderthal admixture
4. Western diseases selected for Western immune responses
One of the interesting things about the Neanderthal DNA hanging around in people is that it appears to code for certain immune responses. West Hunter recently had a great post (TLRs, PAMPs, and Alley Oop) detailing how they work, but for our purposes, “provide immunity” is sufficient. Austin Whittall suggests that back when smallpox, influenza, measles, and all of the other Western diseases tore through the Native Americans, killing about 90% of them, the guys who had more Neanderthal DNA were more likely to survive because they were more likely to be immune to the same stuff as Europeans. By contrast, those Indians with less Neanderthal DNA may have had less immunity to the European diseases, and so been more likely to die, leaving behind a population of high-Neanderthal DNA people.
A couple of papers in Science and Nature recently proposed that Melanesian-related people somehow made it to the rain forest long after the other Indians got to the area. West Hunter helpfully summarizes them.
West Hunter suggests that the Melanesian-related people with their high-Denisovan DNA got to the Americas first, and were then replaced throughout the continents by later invaders, the ancestors of current Indians. The one place the Melanesian-related people managed to survive was in the depths of the rainforest, a very difficult place to conquer. Even today, there are “uncontacted tribes” living in the Amazon rainforest; if anywhere were a good spot for a group of humans to avoid getting conquered, the depths of the rainforest is a good one.
7. The low-Neanderthal and low-Denisovan area along the Baja gulf in Mexico.
So what’s up with that? As far as I know, the only people who don’t have any Neanderthal or Denisovan are Africans. (And even there, there’s a little, just due to back-migration from the rest of the world.)
Are these people descended from a totally different group that came directly from Africa?
There’s a tiny ethnic group in the area, called the Seri:
Dona Ramona of the Seri Indians of Sonora, Mexico
According to the Wikipedia, the Seri speak a language isolate–that is, their language, like Basque, doesn’t appear to be related to any other language on Earth–and they are not culturally connected with any of their neighbors. They’ve also held out significantly against Spanish and Mexican assimilation. In other words, they might very well be a totally isolated population that is not related at all to any of their neighbors.
The two different “real” maps how different things because they come from different scientists who came up with different data, but the overall picture is similar–if you look closely, both maps show a hotspot in Israel, for example. The second map looks less detailed, (hence their miss of several Middle Eastern hotspots,) but has a wider global range, which is obviously useful for our purposes. They also help show the importance of not putting too much stock in any single study about the distribution of a particular gene or allele or whathaveyou; different scientists come up with different numbers.
At any rate, while this could be just a totally random coincidence, if it isn’t, it’s awfully interesting, isn’t it? I know the Egyptians circumnavigated Africa; the Carthaginians and Phoenicians were also noted sea-farers. Or perhaps some other group I know nothing about from the region, before folks started keeping good records. Who knows?
8. Other people’s theories: Neanderthals, Denisovans, and H erectus made it to America before we did, and H Sapiens intermixed with them after they arrived; humans evolved in American, and then migrated to the rest of the world from there.
