Two Denisovan Admixture Events?

Recent genetic analysis suggests that humans mated with the mysterious Denisovans not once, but twice

Asian genomes carry introgressed DNA from Denisovans and Neanderthals

East Asians show evidence of introgression from two distinct Denisovan populations

South Asians and Oceanians carry introgression from one Denisovan population

I can’t read the whole paper, because it’s paywalled, but if correct, this is quite the change. Previously, only small amounts of Denisovan were detected in East Asians, while large amounts (2-6%) were detected in Oceanians (ie, Melanesians, Papuans, and Australian Aborigines.) 

According to Wikipedia:

Statistical analysis of genomic DNA sequences from different Asian populations indicates that at least two distinct populations of Denisovans existed,[50][51] and that a second introgression event from Denisovans into humans occurred. A study of Han ChineseJapanese and Dai genomes revealed that modern East Asian populations include two Denisovan DNA components: one similar to the Denisovan DNA found in Papuan genomes, and a second that is closer to the Denisovan genome from the Altai cave. These components were interpreted as representing separate introgression events involving two divergent Denisovan populations. South Asians were found to have levels of Denisovan admixture similar to that seen in East Asians, but this DNA only came from the same single Denisovan introgression seen in Papuans.[52]  …

The Denisovans, in case you’re new here, are a human species similar to the Neanderthals who lived… well, we’re not sure exactly where they lived, other than the Altai Cave, Siberia. We also don’t know what they looked like, because we have only found a few of their bones–a finger bone and some teeth–but they might have looked a bit like the Red Deer Cave People. Remarkably, though, these were in good enough condition (Siberia preserves things very well,) to allow scientists to extract sufficient DNA to determine that they are indeed a human species, but one that split from the ancestors of Homo sapiens about 600,000-750,000 years ago, and from the Neanderthals about 200,000 years later. 

Just as Homo sapiens mated with Neanderthals, so Denisovans mated with Neanderthals and Homo sapiens–the human family tree is growing increasingly complex. 

We don’t know exactly where these interbreeding events happened, since we know so little about the Denisovans (at least one of the Neanderthal interbreeding events probably happened in the Middle East, given that all non-Africans [and some Africans] have Neanderthal DNA,) but a clue lies in the DNA of the Negrito peoples. 

The Negritoes are a variety of peoples who live in south east Asia and, like the Pygmies of Africa, are rather short. Some of them, like the Aeta of the Philippines, have almost Papuan levels of Denisovan admixture, while others, like the Onge of India, have almost none. Assuming the Negritos are related to each other and not just isolated examples of island dwarfism, this suggests that the interbreeding event really did take places somewhere east of the major Indonesian islands of Sumatra and Borneo (which probably weren’t islands at the time, but connected to the mainland). The Denisovans may have been clever enough to build boats and cross the Wallace Line, surviving in the more isolated islands of Indonesia and the Philippines. 

On a related note, the article I just linked to from John Hawks, “This is where Scientists Might Find the Next Hobbits,” is truly excellent: 

In May, an international team of scientists led by Thomas Ingicco revealed new archaeological findings from Kalinga, in the northernmost part of Luzon, Philippines. Until now, scientists have mostly assumed that the Philippines were first inhabited by modern humans, only after 100,000 years ago. But the artifacts unearthed by Ingicco and coworkers were much older, more than 700,000 years old. …

Luzon was never connected to the Asian mainland, even when sea level was at its lowest during the Ice Ages. To get there, ancient hominins had to float. Who were they, and how did they get there?

Timeline of ancient Indonesian and Filipino hominin findings, from John Hawks’s article

I recommend you read the whole thing.

What’s all of this Denisovan DNA good for, anyway? Quoting Wikipedia again:

The immune system’s HLA alleles have drawn particular attention in the attempt to identify genes that may derive from archaic human populations. Although not present in the sequenced Denisova genome, the distribution pattern and divergence of HLA-B*73 from other HLA alleles has led to the suggestion that it introgressed from Denisovans into humans in west Asia. As of 2011, half of the HLA alleles of modern Eurasians represent archaic HLA haplotypes, and have been inferred to be of Denisovan or Neanderthal origin.[54] The apparent over-representation of these alleles suggests a positive selective pressure for their retention in the human population. A higher-quality Denisovan genome published in 2012 reveals variants of genes in humans that are associated with dark skin, brown hair, and brown eyes – consistent with features found with Melanesians today.[16] A study involving 40 Han Chinese and 40 people of ethnic Tibetan background identified a region of DNA around the EPAS1 gene that assists with adaptation to low oxygen levels at high altitude found in Tibetans is also found in the Denisovan genome.[55][56] In Papuans, introgressed Neanderthal alleles have highest frequency in genes expressed in the brain, whereas Denisovan alleles have highest frequency in genes expressed in bones and other tissues.[57]

It is a great era in genetics. 

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Neanderthal DNA–hey!–what is it good for?

Quite a bit.

First, a bit of history:

neanderthalmap
map of Neanderthal DNA in humans

It appears that there were (at least) 3 main cross-breeding events with Neanderthals. The first event most likely happened when one small band of humans had left Africa and ventured into the Middle East, where Neanderthals were living. The DNA acquired from that partnership can be found in all modern non-Africans, since they are all descended from this same group. (Since there has also been back-migration from the Middle East into Africa sometime in the past 70,000 years, many African groups also have a small amount of this DNA.)

Soon after, the group that became the Melanesians, Papuans, and Aborigines split off from the rest and headed east, where they encountered–and interbred with–the mysterious Denisovans, a third human species that we know mostly from DNA. Various sources claim this happened before the second neanderthal inter-breeding event, but just looking at the amount of admixed neanderthal in Oceanans suggests this is wrong.

Meanwhile, the rest of the non-African humans, probably still living in the Middle East or Eurasian Steppe, encountered a second band of Neanderthals, resulting in a second admixture event, shared by all Asians and Europeans, but not Melanesians &c. Then the Asians and Europeans went their separate ways, and the Asians encountered yet a third group of Neanderthals, giving them the highest rates of Neanderthal ancestry.

nature-siberian-neanderthals-17.02.16-v2

During their wanderings, some of these Asians encountered Melanesians, resulting in a little Denisovan DNA in today’s south Asians (especially Tibetans, who appear to have acquired some useful adaptations to Tibet’s high altitude from ancient Denisovans.)

There were other interbreeding events, including a much older one that left homo sapiens DNA in Neanderthals, and one that produced Denny, a Neanderthal/Denisovan hybrid. There were also interbreeding events in Africa, involving as-yet unidentified hominins. (In the human family tree to the right/above, Melanesians are included within the greater Asian clade.)

Who married whom? So far, we’ve found no evidence of Neanderthal mitochondrial DNA–passed from mothers to their children–in modern humans, so the pairings most likely involved Neanderthal men and human women. But we have also found extremely little Neanderthal DNA on the Y chromosome–so it is likely that they only had female children, or any male children they had were infertile.

Anthropogenesis-DenisovaAlleleMapInterestingly, we find higher amounts of Neanderthal DNA in older skeletons, like the 40,000 year old Tianyuan Man, or this fellow from Romania with 10% Neanderthal DNA, than in modern humans. Two potential explanations for the decrease: later mixing with groups that didn’t have Neanderthal DNA resulted in dilution, or people with more Neanderthal DNA just got out-competed by people with less.

Given the dearth of DNA on the Y chromosome and the number of diseases linked to Neanderthal DNA, including Lupus, Crohn’s, cirrhosis, and Type-2 diabetes, the fact that morphological differences between Sapiens and Neanderthals are large enough that we classify them as different species, and the fact that Neanderthals had larger craniums than Sapiens but Sapiens women attempting to give birth to hybrid children still had regular old Sapiens pelvises, gradual selection against Neanderthal DNA in humans seems likely.

However, the Neanderthals probably contributed some useful DNA that has been sorted out of the general mix and come down the ages to us. For example, the trait that allows Tibetans to live at high altitudes likely came from a Denisovan ancestor:

Researchers discovered in 2010 that Tibetans have several genes that help them use smaller amounts of oxygen efficiently, allowing them to deliver enough of it to their limbs while exercising at high altitude. Most notable is a version of a gene called EPAS1, which regulates the body’s production of hemoglobin. They were surprised, however, by how rapidly the variant of EPAS1spread—initially, they thought it spread in 3000 years through 40% of high-altitude Tibetans, which is the fastest genetic sweep ever observed in humans—and they wondered where it came from.

Modern humans have Neanderthal DNA variants for keratin (a protein found in skin, nails, hair, etc.,) and UV-light adaptations that likely helped us deal with the lower light levels found outside Africa. There’s circumstantial evidence that microcephalin D could have Neanderthal origins (it appeared about 37,000 years ago and is located primarily outside of Africa,) but no one has found microcephalin D in a Neanderthal, so this has not been proven. (And, indeed, another study has found that Neanderthal DNA tends not to be expressed in the brain.)

Yet on the other hand, Neanderthal admixture affected sapiens’ skull shapes:

Here, using MRI in a large cohort of healthy individuals of European-descent, we show that the amount of Neanderthal-originating polymorphism carried in living humans is related to cranial and brain morphology. First, as a validation of our approach, we demonstrate that a greater load of Neanderthal-derived genetic variants (higher “NeanderScore”) is associated with skull shapes resembling those of known Neanderthal cranial remains, particularly in occipital and parietal bones. Next, we demonstrate convergent NeanderScore-related findings in the brain (measured by gray- and white-matter volume, sulcal depth, and gyrification index) that localize to the visual cortex and intraparietal sulcus. This work provides insights into ancestral human neurobiology and suggests that Neanderthal-derived genetic variation is neurologically functional in the contemporary population.

(Not too surprising, given Neanderthals’ enormous craniums.)

Homo sapiens also received Neanderthal genes affecting the immune system, which were probably quite useful when encountering new pathogens outside of Africa, and genes for the “lipid catabolic process,”[19] which probably means they were eating new, fattier diets that Neanderthals were better adapted to digest.

Even Neanderthal-derived traits that today we cast as problems, like Type II Diabetes and depression, might have been beneficial to our ancestors:

“Depression risk in modern human populations is influenced by sunlight exposure, which differs between high and low latitudes, and we found enrichment of circadian clock genes near the Neanderthal alleles that contribute most to this association.”

Why would we find an association between Neanderthal DNA and circadian clock genes? Neanderthals had thousands of years more exposure to Europe’s long nights and cold winters than homo Sapiens’; it is unlikely that they developed these adaptations in order to become less well-adapted to their environment. It is more likely that Neanderthals downregulated their activity levels during the winter–to put it colloquially, they hibernated.

No problem for furry hunter-gatherers who lived in caves–much more problematic for information age workers who are expected to show up at the office at 9 am every day.

Type II diabetes affects digestion by decreasing the production of insulin, necessary for transporting converting carbs (glucose) into cells so it can be transformed into energy. However, your body can make up for a total lack of carbs via ketosis–essentially converting fats into energy.

Our hunter-gatherer ancestors–whether Neanderthal or Sapiens–didn’t eat a lot of plants during the European and Siberian winters because no a lot of plants grow during the winter. If they were lucky enough to eat at all, they ate meat and fat, like the modern Inuit and Eskimo.

And if your diet is meat and fat, then you don’t need insulin–you need ketosis and maybe some superior lipid digestion. (Incidentally, the data on ketogenic diets and type II diabetes looks pretty good.)

In sum, Neanderthal and Denisovan DNA, while not always useful, seems to have helped Homo sapiens adapt to colder winters, high altitudes, new pathogens, new foods, and maybe changed how we think and perceive the world.

 

 

Which Groups Have the most Neanderthal and Denisovan DNA?  

 

beautifulneanderthalDenisovan
Neanderthal and Denisovan contributions to different populations by chromosome (source)

Here are the numbers I’ve found so far for Neanderthal and Denisovan DNA in different populations:

 et al, in The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans, 2016, report:

Native Americans: 1.37%
Central Asia: 1.4%
East Asia: 1.39%
Oceana (Melanesians): 1.54%
South Asia: 1.19%
Europeans: 1.06%

(I have seen it claimed that the high Neanderthal percents for Oceanan populations (that is, Melanesians and their relatives,) could be a result of Denisovan DNA being incompletely distinguished from Neanderthal.)

Prufer et al, [pdf] 2017, report somewhat higher values:

East Asians: 2.3–2.6%
Europeans: 1.8–2.4%

While Lohse and Frantz estimate an even higher rate of between 3.4–7.3% for Europeans and East Asians. (They found 5.9% in their Chinese sample and 5.3% in their European.)

The Mixe and Karitiana people of Brazil have 0.2% Denisovan (source); other estimates for the amount of Denisovan DNA in Native populations are much lower–ie, 0.05%.

I found an older paper by Prufer et al with estimates for three Hispanic populations, but doesn’t clarify if they have Native American ancestry:

Population Individuals Neandertal ancestry (%)
Autosomes X
Europeans CEU–Euros from Utah 85 1.17±0.08 0.21±0.17
FIN–Finnish 93 1.20±0.07 0.19±0.14
GBR–British 89 1.15±0.08 0.20±0.15
IBS–Spain 14 1.07±0.06 0.23±0.18
TSI–Tuscan 98 1.11±0.07 0.25±0.20

East Asians CHB–Han Chinese Beijing 97 1.40±0.08 0.30±0.21
CHS–Han Chinese South 100 1.37±0.08 0.27±0.21
JPT–Japan, Tokyo 89 1.38±0.10 0.26±0.21

Americans CLM: Colombians from Medellin 60 1.14±0.12 0.22±0.16
MXL: Mexicans from LA 66 1.22±0.09 0.21±0.15
PUR: Puerto Ricans 55 1.05±0.12 0.20±0.15

Africans LWK: Luhya in Webuye, Kenya 97 0.08±0.02 0.04±0.07
ASW: African Americans South West US 61 0.34±0.22 0.07±0.11

Since the paper is older, all of its estimates are lower than current estimates, because we now have more Neanderthal DNA to compare against. However, you can still see the general trend.

The difference between “autosomes” and “X” highlighted here is that (IIRC) autosomes includes all chromosomes except the XY pair, and X is the X from that pair. They’re breaking them up this way because the X chromosome tends to have very little Neanderthal on it (and the Y even less), probably because Neanderthal DNA on these particular chromosomes was selected against.

Neanderthal DNA appears to have been selected for in areas that control hair and skin–people who had just left Africa were adapted to the African environment, and Neanderthal hair and skin traits helped them survive in colder, darker winters. We also see a lot of Neanderthal DNA influencing inflammation/immune response–these may have helped people fend off new diseases. But we see almost no Neanderthal (or Denisovan) DNA in areas of the genome that code for sperm, eggs, testes, ovaries, etc. These parts of people were probably already finely tuned to work together, didn’t need to change with the environment, and changing anything probably just made them less efficient–so Neanderthal (and Denisovan) DNA on the X and Y chromosomes has been purged from the Homo Sapiens gene pool.

North African Populations Carry Signature of Admixture with Neanderthals reports its data relative to the European average (which I believe is the CEU pop, 1.17%, so I’ll do the math for you to figure how much Neanderthal they have.)

Algeria 44.57% = 0.52% Neanderthal
Tunisia 100.16% = 1.172 N
Tunisia 138.13% = 1.6% N (This is an interesting population that has been highly endogamous and thus better reflects historical populations in the area.)
Egypt 58.45% = 0.68% N
Libya 56.36% = 0.66% N
Morroco North 69.17% = 0.81% N
Morocco South 17.90% = 0.21% N
Saharawi 50.90% = 0.6% N
Canary Island* 101.44% = 1.187% N
China Beijing 193.43% = 2.26 % N
China 195.41% = 2.29% N
Texas Indu Gupti 84.37% =0.987% N
Andalusia*118.66% = 1.39% N
Tuscan 94.90% = 1.11% N
Basque BASC 129.48% = 1.51% N
Galicia* GAL 115.86% = 1.36% N
Yoruba YRI  0.00% = 0% N
Luyha LWK  −14.89% = N

The authors note that they are not sure how the Luyha received a negative score–perhaps the presence of admixed DNA from yet another species is interfering with the results.

According to Wikipedia:

Denisovan DNA is most commonly found in Melanesians, Papulans, Aboriginal Australians and Aboriginal Filipinos, who all have similar amounts around 4-6%, indicating that they probably were all one group when their ancestors met the Denisovans. However, the similar-looking but historically quite isolated Onge people have no Denisovan–so they split off before the event.

In Papuans, Neanderthal DNA tends to be expressed in brain tissue, Denisovan in bones and other tissues.

Asians have a small amount of Denisovan DNA; Tibetans have a particular gene that lets them absorb oxygen effectively at high altitudes that they got from the Denisovans.

The Mende People of Sierra Leon may derive 13% of their DNA from an as-yet unknown hominin species (ancient DNA and bones do not preserve well in parts of Africa, so finding remains and identifying the species may be difficult.)

The Yoruba derive 8 or 9% of their DNA from the same hominin.

Masai have a small fraction of Neanderthal–since they are 30% non-African, probably about 0.35% of their genome–but you can read the paper yourself. 

Biaka Pygmies and Bushmen (San): 2% from an unknown archaic.

With more testing, better and more comprehensive numbers are sure to turn up.

Greatest Hits: Native Americans and Neanderthal DNA.

Native-American-populations
Source: Ancient Beringians: A Discovery Changing Early Native American History

Over the years, a few of my posts have been surprisingly popular–Turkey: Not very Turkic, Why do Native Americans Have so much Neanderthal DNA?, Do Black Babies have Blue Eyes? and Can Ice packs help stop a seizure (in humans)?

It’s been a while since these posts aired, so I thought it was time to revisit the material and see if anything new has turned up.

Today, lets revisit Native Americans and Neanderthal DNA:

I’m sorry, but I no longer think Native Americans (aka American Indians) have higher than usual levels of Neanderthal DNA. Sorry. Their Neanderthal DNA levels are similar to (but slightly lower than) those of other members of the Greater Asian Clade. They also have a small amount of Denisovan DNA–at least some of them.

Why the confusion? Some Neanderthal-derived alleles are indeed more common in Native Americans than in other peoples. For example, the Neanderthal derived allele SLC16A11 occurs in 10% of sampled Chinese, 0% of Europeans, and 50% of sampled Native Americans. (Today, this gene makes people susceptible to Type 2 diabetes, but it must have been very useful to past people to be found in such a large percent of the population.)

neanderthalmap

And there was one anomalously high Neanderthal DNA measure in Natives living near the Great Slave Lake, Canada. (Look, I didn’t name the lake.)

But this doesn’t mean all Native Americans possess all Neanderthal alleles in greater quantities.

So how much Neanderthal do Native Americans have? Of course, we can’t quite be sure, especially since only a few Neanderthals have even had their DNA analyzed, and with each new Neanderthal sequenced, we have more DNA available to compare against human genomes. But here are some estimates:

beautifulneanderthalDenisovan
Neanderthal and Denisovan contributions to different populations by chromosome (source)

 et al, in The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans, report:

Native Americans: 1.37%
Central Asia: 1.4%
East Asia: 1.39%
Oceana (Melanesians): 1.54%
South Asia: 1.19%
Europeans: 1.06%

I have seen it claimed that the high Neanderthal percents for Oceanan populations (that is, Melanesians and their relatives,) could be a result of Denisovan DNA being incompletely distinguished from Neanderthal.

Prufer et al, [pdf] 2017, report somewhat higher values:

East Asians: 2.3–2.6%
Europeans: 1.8–2.4%

While Lohse and Frantz estimate an even higher rate of between 3.4–7.3% for Europeans and East Asians. (They found 5.9% in their Chinese sample and 5.3% in their European.)

The Mixe and Karitiana people of Brazil have 0.2% Denisovan (source); other estimates for the amount of Denisovan DNA in Native populations are much lower–ie, 0.05%.

I found an older paper by Prufer et al with estimates for three Hispanic populations, but doesn’t clarify if they have Native American ancestry:

CLM–Colombians from Medellin: 1.14%
MXL–Mexicans in LA: 1.22%
PUR–Puerto Rico: 1.05%

Since this is an older paper, all of its estimates may be on the low side.

The absolute values of these numbers is probably less important than the overall ratios, since the numbers themselves are still changing as more Neanderthal DNA is uncovered. The ratios in different papers point to Native Americans having, overall, about the same amount of Neanderthal DNA as their relatives in East Asia.

Melanesians, though. There’s an interesting story lying in their DNA.

Denny: the Neanderthal-Denisovan Hybrid

Carte_Neandertaliens
Neanderthal Sites (source: Wikipedia)

Homo Sapiens–that is, us, modern humans, are about 200-300,000 years old. Our ancestor, Homo heidelbergensis, lived in Africa around 700,000-300,000 years ago.

Around 700,000 years ago, another group of humans split off from the main group. By 400,000 years ago, their descendants, Homo neanderthalensis–Neanderthals–had arrived in Europe, and another band of their descendants, the enigmatic Denisovans, arrived in Asia.

While we have found quite a few Neanderthal remains and archaeological sites with tools, hearths, and other artifacts, we’ve uncovered very few Denisovan remains–a couple of teeth, a finger bone, and part of an arm in Denisova Cave, Russia. (Perhaps a few other remains I am unaware of.)

Yet from these paltry remains scientists have extracted enough DNA to ascertain that no only were Denisovans a distinct species, but also that Melanesians, Papuans, and Aborigines derive about 3-6% of their DNA from a Denisovan ancestors. (All non-African populations also have a small amount of Neanderthal DNA, derived from a Neanderthal ancestors.)

If Neanderthals and Homo sapiens interbred, and Denisovans and Homo sapiens interbred, did Neanderthals and Denisovans ever mate?

nature-siberian-neanderthals-17.02.16-v2
The slightly more complicated family tree, not including Denny

Yes.

The girl, affectionately nicknamed Denny, lived and died about 90,000 years ago in Siberia. The remains of an arm, found in Denisova Cave, reveal that her mother was a Neanderthal, her father a Denisovan.

We don’t yet know what Denisovans looked like, because we don’t have any complete skeletons of them, much less good skulls to examine, so we don’t know what a Neanderthal-Denisovan hybrid like Denny looked like.

But the fact that we can extract so much information from a single bone–or fragment of bone–preserved in a Siberian cave for 90,000 years–is amazing.

We are still far from truly understanding what sorts of people our evolutionary cousins were, but we are gaining new insights all the time.

Do Chilblains Affect Blacks More than Whites?

toes afflicted with chilblains
toes afflicted with chilblains

While tromping through a blizzard, seeking insight into circum-polar peoples, I discovered a condition called chilblains. The relevant Wikipedia page is rather short:

Chilblains … is a medical condition that occurs when a predisposed individual is exposed to cold and humidity, causing tissue damage. It is often confused with frostbite and trench foot. Damage to capillary beds in the skin causes redness, itching, inflammation, and sometimes blisters. Chilblains can be reduced by keeping the feet and hands warm in cold weather, and avoiding extreme temperature changes. Chilblains can be idiopathic (spontaneous and unrelated to another disease), but may also be a manifestation of another serious medical condition that needs to be investigated.

The part they don’t mention is that it can really hurt.

The first HBD-related question I became interested in–after visiting a black friend’s house and observing that she was comfortable without the AC on, even though it was summer–is whether people from different latitudes prefer different temperatures. It seems pretty obvious: surely people from Yakutsk prefer different temperatures than people from Pakistan. It also seems easy to test: just put people in a room and give them complete control over the thermostat. And yet, I’d never heard anyone discuss the idea.

Anyway, the perfunctory Wikipedia page on chilblains mentioned nothing about racial or ethnic predisposition to the condition–even though surely the Eskimo (Inuit) who have genetic admixture from both ice-age Neanderthals and Denisovans:

“Using this method, they found two regions with a strong signal of selection: (i) one region contains the cluster of FADS genes, involved in the metabolism of unsaturated fatty acids; (ii) the other region contains WARS2 and TBX15, located on chromosome 1.” …

“TBX15 plays a role in the differentiation of brown and brite adipocytes. Brown and brite adipocytes produce heat via lipid oxidation when stimulated by cold temperatures, making TBX15 a strong candidate gene for adaptation to life in the Arctic.” …

“The Inuit DNA sequence in this region matches very well with the Denisovan genome, and it is highly differentiated from other present-day human sequences, though we can’t discard the possibility that the variant was introduced from another archaic group whose genomes we haven’t sampled yet,” Dr. Racimo said.

The scientists found that the variant is present at low-to-intermediate frequencies throughout Eurasia, and at especially high frequencies in the Inuits and Native American populations, but almost absent in Africa.

Sub-Saharan Africans have their own archaic admixture, but they have very little to no ice-age hominin–which is probably good for them, except for those who’ve moved further north.

Imagine my surprised upon searching and discovering very little research on whether chilblains disproportionately affects people of different races or ethnicities. If you were a dermatologist–or a genetically prone person–wouldn’t you want to know?

So here’s what I did find:

The National Athletic Trainers Association Position Statement on Cold Injuries notes:

Black individuals have been shown to be 2 to 4 times more likely than individuals from other racial groups to sustain cold injuries. These differences may be due to cold weather experience, but are likely due to anthropometric and body composition differences, including less-pronounced CIVD, increased sympathetic response to cold exposure, and thinner, longer digits.3,6

I think CIVD=Cold-Induced Vasodilation

The Military Surgeon: Journal of the Association of Military Surgeons of the United States, Volumes 36-37, states:

c2ijujzucaayfvv

c2ijvyvveaaehdz c2ijw49vqaajuou

The text continues with descriptions of amputating rotting feet.

A PDF from the UK, titled “Cold Injury,” notes:

c2ilp17uaaaonao

Notice that the incidence of chilblains is actually less in extremely cold places than moderately cold places–attributed here to people in these places being well-equipped for the cold.

c2ilp4evqaet4lu

Finally I found a PDF of a study performed, I believe, by the US Military, Epidemiology of US Army Cold Weather Injuries, 1980-1999:

picture-2

While I would really prefer to have more ethnic groups included in the study, two will have to suffice. It looks like trench foot may be an equal-opportunity offender, but chilblains, frostbite, and other cold-related injuries attack black men (at least in the army) at about 4x the rate of white men, and black women 2x as often as white women (but women in the army may not endure the same conditions as men in the army.)

On a related note, while researching this post, I came across this historic reference to infectious scurvy and diabetes, in the Journal of Tropical Medicine and Hygiene, Volumes 4-5 (published in 1902):

c2iou5uviae83si

Note: this is why it is important to discard bad theories after they’ve been disproven. Otherwise, you kill your scurvy victims by quarantining them instead of giving them oranges.

Updated Tentative map of Neanderthal DNA

Picture 1

Based on my previous tentative map of archaic DNA, plus recent findings, eg Cousins of Neanderthals left DNA in Africa, Scientists Report. As usual, let me emphasize that this is VERY TENTATIVE.

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.

Tentative map of Neanderthal (and Denisovan) DNA in humans

I couldn’t find one, so I made one:
neandermap

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.

When I have more data, I’ll update the map.

Sources read:

Dienekes: Neandertal admixture in modern humans

John Hawks: Neandertal ancestry iced, Neandertal introgression 1,000 genomes style

The Atlantic: The Other Neanderthal

1000 Genomes: about

Wang et al, Apparent Variation in Neanderthal Admixture among African Populations is Consistent with Gene Flow from Non-African Populations

 

 

 

 

 

 

Please, please let me know if you find some better lists of the %s of Neanderthal and Denisovan DNA in different populations.

So Why do Native Americans have so much Neanderthal DNA?

Warning: highly speculative post ahead.

As I mentioned the other day:

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).
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)
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.)

Anthropogenesis-DenisovaAlleleMap

So, Native Americans appear to have a ton of Neanderthal DNA. (Relatively speaking.)

Possibilities:

  1. 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: Frequency-of-red-hair-in-Europe

(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:

europe-hair0223--light-h

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

Alternatively, the harsh conditions of life in the Bering Strait–where some scientists think the ancestors of today’s Indians hung out (or “paused”) for thousands of years before the ice sheets opened up to let them through–may have selected for winter adaptations that came from ice-age Neanderthals. I have speculated previously that Type-2 Diabetes may actually be a winter adaptation picked up from Neanderthal DNA; now scientists think this DNA may be responsible for high rates of Type-2 Diabetes in Native Americans.

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.

5. One thing we can say for sure: if the data’s correct, the peopling of the Americas was more complex than previously thought.

There are four areas of particular interest:

A. The highly Neanderthal area in the Pacific Northwest

B. The highly Denisovan area in Brazil

C. The low-Neanderthal area on the South American coast

D. The low-Neanderthal and low-Denisovan area along the Baja gulf in Mexico.

I’ve got nothing on A and C; supply your own theories.

6. Speculations on the origins of high-Denisovan people in Brazil:

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
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.

Some more information on the Seris.

Then I found this interesting map:

map showing global distribution of the HLA-B*73:01 allele
maps showing global distribution of the HLA-B*73:01 allele

I found these maps over on Austin Whittall’s post on Denisovans and America.

Looks like the same spot, doesn’t it?

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.

Neanderthals!

So I still haven’t tracked down anything I consider a good source on the percent of Neanderthal DNA in people from particular regions of Europe, and I should note that at this point, I consider pretty much *everything* in the field of Neanderthal DNA in modern homo Sapiens quite speculative and not nearly has solid as people make it ought to be. But it’s still really interesting stuff, so here goes. I’ll start with a little background information in case you haven’t been following along:

1. Modern people tend to have a little bit of archaic DNA from non-human hominins. Pretty much everyone outside of Africa (including African Americans and even some Africans) has Neanderthal DNA; folks down in Papua New Guinea also have Denisovan DNA (I can’t remember if people outside of PNG have Denisovan.) People in Africa, I hear, have their own admixture from whoever else was living down in Africa. Oh, and people in Tibet have admixture from the hominins who used to live in Tibet before them.

2. Interestingly, the Neanderthal DNA does not appear to be concentrated where you’d think it would be. Sure, Neanderthals themselves hung out primarily in Europe and the Middle East, but American Indians seem to have the most Neanderthal DNA, followed by East Asians. (I consider these findings especially speculative.)

I have noticed in studying maps of different waves of human migrations that where one wave follows another, the first wave ends up way out in the fringes. Take, for example, the parts of Europe where people speak Celtic languages. Celtic languages were once widespread in Europe, covering France, Spain, Britain, Ireland, Switzerland, and a few other places, like possibly a town in Turkey. Today, Celtic languages are spoken in isolated pockets on the outer costs of Ireland, Scotland, and Wales. There are a few other isolated spots on the mainland coast where the languages persisted until fairly recently. Germanic peoples invaded all of these countries, taking them over and imposing their languages, until the Celtic languages are only left at the fringes, in places protected by their isolation.

So, likewise, perhaps Europe itself, being closer to Africa, had more invasions and so ended up with less Neanderthal DNA than the Americas, which were really bloody hard to invade.

There are a lot of other ways one group could get more Neanderthal DNA than another.

3. So how Neanderthal are you? On average, I believe non-African people have about 2.5% Neanderthal DNA.

For perspective, you have 32 great-great-great grandparents, who were probably born around 150 years ago, and 64 great-great-great-great grandparents, whom we’ll just neatly say were born around 170 years ago.

1/32 = 3.1%, so you’d expect to receive about 3.1% of your DNA from each of your 3xGreat Grandparents. 1/64 = 1.6%, so you get about 1.6% from each of your 4X Great Grandparents. So that’s where the average person’s Neanderthal contribution is–it’s like having one Neanderthal ancestor from the mid 1800s.

A lot of people claim to be ethnically Irish based on less.

4. I suspect Europe’s Neanderthal hotspot is Sardinia.

Speculations later.