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DNA reveals we are all genetic mutts (news.harvard.edu)
51 points by mjfl 21 days ago | hide | past | web | favorite | 60 comments



> A similar prehistory occurred in the Iberian Peninsula where a third population, also arrived from the Steppes, joined the hunter-gather and farmer groups. In this case, DNA research shows that the third population was exclusively male: While only 40 percent of the population about 6,000 years ago comes from the Steppes, 100 percent of the Y chromosomes do.

This doesn't say what the author wants it to say. If 100% of the Y chromosomes come from the intrusive population, that doesn't mean that the intrusive population was entirely male. It means that 100% of indigenous males were exterminated, so that (after the intrusion) the male population was entirely intrusive. All the males being intruders is a very different concept from all the intruders being male.


No, it doesn't mean that either (extermination of males). It just means that only Steppe Y-chromosomes survived. This could be the result of extermination, or it could be the result of stochastic drift, or selection, or any number of other scenarios that result in the loss of some set of Y chromosomes.


Realistically, extermination of males is exactly what it means. It cannot be stochastic drift; the pool of chromosomes dying out is too large. It can be selection (it is selection), but it can only be the kind of selection that involves every native male failing to have children at all, because the Y chromosome does not recombine.


First of all, given that we only have a limited sample of the Y-chromosome space, I don't think we can conclude that no native Y-chromosomes actually survived. That aside, it's easy to get selection for specific Y chromosomes without extermination, for example if you have a ruling caste whose males are favored (e.g. by primogeniture) or through preferential mating by lineage. See: the prevalence of the (presumed) Chingisid chromosome here: https://doi.org/10.1086%2F367774


> were exterminated

or expelled, or otherwise prevented from being allowed to breed.


Such as castrated.


From what I've read, that's what the Mongols did. It's also what happened for many indigenous groups in eastern North America. Except that the males were escaped African-American slaves. I'm guessing that it was standard procedure for thousands of years.


> This doesn't say what the author wants it to say.

The way I read it, the author was perfectly aware of this interpretation.


> “No population is, or ever could be, pure,”

Why this obsession with 'purity'? Isn't it obvious that, despite none being pure, some populations are more closely related?


> Isn't it obvious that, despite none being pure, some populations are more closely related?

It is obvious, and the same data shows that groups can be very pure indeed. From this very article:

> Genetics also show that India’s caste system, previously thought to have developed under colonial rule, was in place thousands of years earlier.

First, "previously thought to have developed under colonial rule" is just false. The ancient Greeks wrote about India's caste system, thousands of years ago.

Second, what the data shows is not a record of social structure. It shows that modern Indian castes have practiced endogamy -- mating within the group, with negligible inflow from other groups -- for thousands of years.

Most people would be happy to describe this state of affairs as "pure" ancestry.


> First, "previously thought to have developed under colonial rule" is just false. The ancient Greeks wrote about India's caste system, thousands of years ago.

Correct, the article is flat wrong on this. Indian sources that even predate the Greeks also speak in detail about the societal arrangement.

> Second, what the data shows is not a record of social structure. It shows that modern Indian castes have practiced endogamy -- mating within the group, with negligible inflow from other groups

Yes, but they are still sampled, albeit in varying proportions, from the same source populations, referred to in the literature as ASI and ANI, which are themselves composite groups.


> Yes, but they are still sampled, albeit in varying proportions, from the same source populations, referred to in the literature as ASI and ANI.

Sure, but that was several thousand years ago. Again, most people are perfectly happy to describe unmixed ancestry for the last 2400 years as being "pure", and the castes go back farther than that.


> Again, most people are perfectly happy to describe unmixed ancestry for the last 2400 years as being "pure", and the castes go back farther than that.

Just because "most people" are willing to draw that line at 2400 years doesn't make it a valid argument.

At most you could say that there is genetic evidence to support the hypothesis that the castes have practiced endogamy for a long time, evidenced by their characteristic genetic admixtures from their shared source populations, and that the caste hierarchy is roughly correlated with ANI admixture rate. That doesn't equate to the word "pure" at all.

People are willing to make all sorts of claims about their and others' identities to suit their personal agendas, and it's their right to do so, but they aren't doing science.

What about the many millennia that elapsed between the last major shared human population bottleneck and 2400 years ago?


This was a fascinating comment thread to follow. I've been looking for information on the endogamous groups of India, the early written history of the caste system and the genetics of these groups. Do you have any pointers?


The earliest known literary mention (not written - ancient Indians recorded and passed on their literature orally) of the caste system is the Purusha Sukta hymn from the Rigveda (late 2nd millennium BCE):

https://en.m.wikipedia.org/wiki/Purusha_Sukta

It's interpretation is varied and controversial to say the least.

But one shouldn't confuse the theoretical model presented in the liturgical texts (referred to with the term "varna", meaning "color" or "tone") with the concrete manifestation of traditional endogamous divisions in society (referred to with the term "jati", meaning "station of birth').

The ground reality is more oriented around the complexities of class, tribe, language and occupation, and even physical phenotype, which were then rationalized through the theoretical 4-fold system of caste.

There are parts of India (the southern and eastern parts) where the actual social structure doesn't map as cleanly to the 4-fold system, except among the higher castes. However endogamy and strong caste hierarchy is still just as common in these regions.

In terms of population genetics of South Asia specifically, here is a good place to start:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702070/#__sec2...


you get extra points if you can dress your scientific story as "speaking out against racism".


not sure why you were downvoted, this is exactly why they mentioned purity.



It's a rebuke of the false trope of the purity of racial ancestry which has persisted in many human societies for centuries, occasionally manifesting in the form of events like the Holocaust.

Because that trope has sadly persisted to this day in some quarters, it's falsehood needs to be continually exposed, especially by sciences such as biological anthropology, which were once used to promulgate it.


Actually, it's my impression that some Jewish groups have done a pretty good job at maintaining racial purity. In some cases, leading to ~frequent homozygousity for some nasty recessive mutations.

I don't know the specifics, but I've read that only certified Jews can officially marry in Israel. And the standards are so high that many "Jewish" immigrants don't qualify.

Now that we have DNA testing, I wonder if that will become the standard.


> Actually, it's my impression that some Jewish groups have done a pretty good job at maintaining racial purity.

Because certain very specific subgroups have done this doesn't mean that they are "pure". These in-marrying groups are always descended from mixed populations in the first place, populations that predate the identity badges we ascribe to them today.

Tay Sachs, among the genetic diseases you alluded to, is also present in non Jewish populations, but at a lower rate:

https://www.haaretz.com/jewish/non-jews-increasingly-hit-by-...

> I don't know the specifics, but I've read that only certified Jews can officially marry in Israel. > And the standards are so high that many "Jewish" immigrants don't qualify.

People can convert to Judaism, and even be born into Judaism with one Jewish parent. This is very common among populations outside of Israel.

Large subgroups in Judaism, sephardi, baghdadi, etc, are genetically quite diverse in origin, and are significantly represented among the Israeli population.


> People can convert to Judaism, and even be born into Judaism with one Jewish parent. This is very common among populations outside of Israel.

Yes, but to strict orthodox, they're not really "Jewish".

At one point, I researched rabbinical criteria for determining pedigree and classifying degree of Jewishness. Who can marry who, and how any children are classified. It's mind-boggling. If I have some time while this thread is hot, I'll post some sources.

Edit: Here are some sources. Please note that they're Jewish sources. Not anti-Jewish sources.

http://www.jewishencyclopedia.com/articles/11977-pedigree

https://www.chabad.org/library/article_cdo/aid/4045946/jewis...

https://tikvahfund.org/uncategorized/intermarriage-can-anyth...

https://www.jewishvirtuallibrary.org/marriage-in-judaism

http://www.cohen-levi.org/jewish_genes_and_genealogy/the_dna...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1288118/


> Yes, but to strict orthodox, they're not really "Jewish".

Unless you are seeking to identify as "strict orthodox", why would it matter?

The majority of Jewish groups are welcoming to people from the outside, if they achieve the required objectives in terms of religious and cultural fluency.


I don't really care, now.

But strict orthodox rules do apply in Israel. And that's not so insignificant. It's one reason why I'm in the US and not in Israel.


I don't think it's a rebuke at all. The other side of the coin is to make sure you're the steppe tribes, not the hunter-gatherers. People who care about such things don't really care about purity, they care about winners and losers.


> The other side of the coin is to make sure you're the steppe tribes, not the hunter-gatherers.

This doesn't follow from the researcher's statement at all. Just because the mechanism by which diversity happened thousands of years ago was often terrible doesn't mean we need to project that upon today, when we have much better mechanisms for genetic diversity, like immigration.

We, as a human society, have improved just a bit.


> We, as a human society, have improved just a bit.

I think it's debatable. The tribes are much bigger but really little has changed.


It's fascinating that my comment above rebuking racial purity theories is so controversial (evidenced by the oscillating down and up votes for a full day), yet there are no follow up comments supporting racial purity theory in general, just a discussion about the relative genetic isolation of one group?

It's surprising that rebuking racial purity as a concept would be so controversial today on a forum like this.


There's also this:

> Once upon a time, 4,000 to 8,000 years after humanity invented agriculture, something very strange happened to human reproduction. Across the globe, for every 17 women who were reproducing, passing on genes that are still around today—only one man did the same.

So it seems like this was a common pattern.

https://psmag.com/environment/17-to-1-reproductive-success

https://genome.cshlp.org/content/early/2015/03/13/gr.186684....


> Genetics also show that India’s caste system, previously thought to have developed under colonial rule, was in place thousands of years earlier.

This is such a shockingly ignorant statement that I wonder what Harvard is teaching these days.


Look up David Reich. The actual finding is that many Jātis show genetic evidence that interbreeding with other Jātis has been negligible over the past 2000 years. It's not necessarily a statement of the social relations between the Jātis, let alone the varnas.


Genetics also show that India’s caste system, previously thought to have developed under colonial rule, was in place thousands of years earlier.

“Colonial rule” means British rule presumably. I always assumed the caste system long pre-dated it, considering how entrenched it seems to be.


The British exploited it, and under them aspects of it became more rigid, but it long predates them.


The data shows there was less than one inter-caste marriage per caste pair per generation for the last few thousand years. What was left to become "more rigid" than that under the British?


For one thing, there is often a subcaste structure within each local caste itself. The subcastes of a caste who received British patronage, i.e. jobs in the colonial administration, would preferably marry only among themselves.

Of course, this was about preservation of wealth and power, and not so different from similar marriage practices among wealthy classes in England (as depicted in Downton Abbey)

The British didn't invent the sub-castes, but they effectively exploited them.



>What makes Dr. Watson’s and Mr. Wade’s statements so insidious is that they start with the accurate observation that many academics are implausibly denying the possibility of average genetic differences among human populations, and then end with a claim — backed by no evidence — that they know what those differences are and that they correspond to racist stereotypes.

Perhaps there is no hard evidence because nobody is willing to risk their lively-hood over researching such claims. Just look at what they did to Dr. Watson. Heck, a few paragraphs above Reich was talking about African-Americans being genetically predisposed to prostate cancer as if it was a highly controversial topic.


Well, the problem is we probably can't find anyone to sponsor to study to determine if once and for all, whites are prone to psychosis and mass murder via guns.


Now that is quite the switch of topic. The only known research of race differences in psychopathy is of Richard Lynn's 2002 studies on the topic. In this, Lynn does point to whites being more prone to psychosis than on average. I do know of some controversy of Richard Lynn's work, and here is a response paper to such: https://web.archive.org/web/20130108233748/http://riskreduct...

Regarding school shootings in particular, my personal guess is that such sour actions on the average are merely a symptom of a hole in America's conscious, in that these semi-affluent white boys have lost meaning in life, and do not care if the actions they commit are grave. Of particular note is you do not see boys of abject poverty commit these actions, as they are more focused on not starving (and thus have something obviously meaningful to their life to prioritize).


Psychopathy, i.e. antisocial personality disorder, and psychosis, the state of experiencing delusions and/or hallucinations, are two very different things.


Oh yes, my apologies. Although in my defense I would connect psychopathy with school shootings rather than psychosis. And by a brief search it seems that in America whites on average are diagnosed with psychosis much less often than blacks and hispanics: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4274585/


"treat each human being as an individual and to empower all people, regardless of what hand they are dealt from the deck of life"

Well that's certainly better than the third one.


> The Steppe migration resulted in a 90 percent replacement of the population.

>While only 40 percent of the population about 6,000 years ago comes from the Steppes, 100 percent of the Y chromosomes do.

From reading this article it seems another way that this could be phrased, is that we are all the descendants of perpetrators of genocide.


Don't forget the rape!

100% of your Ys coming from one place is the opposite of "mutt", too. But the only way you can get to do race science is by coming to the conclusion "There's no such thing as race" first, and making the details sound boring enough that nobody asks.


Apparently you're unfamiliar with the sorry state of the gene content of the Y chromosome.


The concept of race has always sounded like total bullshit to me. Do you have a definition that makes any sense?


Sequence the world and run them through a clustering algorithm, picking how many clusters you get:

2 clusters: African and non-African

5 clusters: African, European, Asian, PNG/Australian Aboriginal, Native Americans

All the way to:

1 billion clusters: Individual families

When most people think of race they are talking about the number of groups that make clusters of major continents, where there wasn't much gene flow until 1492.

Google PCA ancestry (PC term for race) eg gnomAD:

https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcSZ-l...

Self reported race matches genetically determined race at rates in the high 90s.

A way to think about it without clustering etc:

People separated (usually by geography) long enough that they bred mostly amongst themselves, and developed characteristics different than other groups.

Yes, you can walk from Amsterdam to Beijing and see a gradient of people the whole way - but that doesn't mean you can't tell the difference between a Chinese person and a Dutchman.


Easy: the definition is what most people mean when they use the term. Paraphrased: phenotypic characteristics that correlate with ancestry.


How about 'ethnic group' then instead? The evidence of difference is right before our eyes. Just watch athletics!


Yeah, the title ought to be something like "DNA reveals many of us are descendants of genocide and rape".

Edit: So I clearly have some Mongol heritage. And so does my wife, who's Ukrainian. One of her grandmothers could have easily passed as a native in Mongolia.


I wonder how many of these genetic migrations were peaceful.


probably very few, if the old testament or the huge proportion of ancient skeletons that died violent deaths serve as any guide. which is why I think this story by Reich is very tone deaf. It's hard to see how a 90% population replacement promotes feelings of unity and hand-holding.

One imagines a superposition of a video feed of the invasion of the steppe-people on horseback, stampeding the native defenses, cutting the male children's throats and raping the women, with a video a David Reich being like "we're all a little mixed".


Tone deaf indeed. It seems common for people not to ascribe a full measure of humanity to humans from the (distant enough) past. Thought exercise: are there any large-scale population replacements happening today, and how do people feel about that? Surely not a kumbaya feeling I'd bet.


In the recent past: the Americas, Australia, New Zealand, Fiji?, etc.

Current: Tibet, West Papua, Rwanda?, Northern Europe perhaps?


Add Xinjiang to the list of current ones - from https://www.nytimes.com/2019/03/02/world/asia/china-muslim-d..., flagged off the HN front page: "Decades of migration by Han, China’s dominant ethnic group, have transformed Xinjiang, fueling Uighur anxieties. Uighurs, once the majority, are 46 percent of the region’s 22 people million people, Han are 40 percent and Kazakhs 7 percent, according to government estimates."


It's easy to find these in the relatively recent past. See: North America.

quoyz 21 days ago [flagged]

David Reich you say.


of course we are all mutts, we all evolved from bacteria. the question is the relative purity. "is the race pure from this period to this period" is what people mean when they mention purity. When a jew chooses a mate, they are only concerned if their mate has pure jewish ancestry from the last 2000 years.


That doesn't equate to "relative purity" at all. The number of ancestors someone has 66 generations in the past (approx 2000 years) is enormous. We can get around this by making value judgements that say "only the direct matrilineal line ancestors count" or "only the direct patrilineal line ancestors count", but ideas like that are absolutely human value judgements made as a reaction to the overwhelming complexity above, and have no basis in biology. These value or worth of those judgements are also artificially enforced and were not robustly adhered to historically. We are indeed all mutts, and every credible analysis for the last century has shown "race purity" is an abstraction that is absurd to the point of lunacy.


> We are indeed all mutts

I get why Reich says things like this, but you have to ask what it would mean not to be a "mutt". Is that even physically possible? If not, why do we need DNA testing of ancient skeletons to prove this?




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