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Friends are as genetically similar as fourth cousins (pnas.org)
281 points by gwern on July 12, 2016 | hide | past | favorite | 133 comments

In case you were also wondering what a "fourth cousin" was, someone who shares a pair of great-great-great grandparents[0]. Wikipedia has a great set of diagrams[1] in case you're also confused about first, second, or third cousins. I figure through induction you can presume any nth and nth removed from that page (I foolishly thought 3rd was where people arbitrarily stopped keeping count....)

[0] https://www.reference.com/family/fourth-cousin-7b40e096c6d65...

[1] https://en.wikipedia.org/wiki/Cousin#First_cousins

I get mad at people who think sons of first-cousins are second-cousins all the time -- and, frankly, almost everyone I know think this way.

I'm glad you linked to this Wikipedia article that proves I'm not mad into thinking there is a simple logic pattern that can be applied to cousinship.

However, this "once removed" notation is crazy. Why not second-uncle for parents of second-cousins and so on?

Pardon me for my ignorance, but wouldn't sons of first cousins be second cousins?

Generally the "1st/2nd" bit denotes how many generations up you have to go to find a common ancestor, and "removed" is how many generations removed the other person is from that generation.

You are, to your your first cousin's child, who is your first cousin once-removed, a second cousin once-removed.

Language quirk :) The son of my first cousin is my first cousin once removed. My son and my cousin's son are second cousins.

Actually the term "second cousin" does not have a concrete meaning. It can mean a true second cousin, or it can also mean a generation removed from a first cousin. The "once removed" terminology was introduced to compensate for this ambiguity.

Ah, I read "sons of first cousins" as "two people who are first cousins to each other each have a son". "A son of a first cousin" would be much less ambiguous. In fact, even knowing what you meant, I have a hard time reading the meaning you intended to convey.

Another clearer way to phrase it would be "sons of my first cousin are not my second cousins".

No! Stop the removed madness!

He must be referring to one's own first cousin's children. Not the children of two first cousins.

yes. the wording and the fact that other people seemed to agree with the op made me spend way too much time on this.

You can call them anything you like, I'm just saying that you shouldn't.

That's what I use.

2nd uncle, 2nd grand aunt

Fun fact: in Russian a first cousin is a 2nd Brother/Sister, a 2nd cousin is a 3rd Brother/Sister and so on.

That makes a lot of sense! The distinction between sibling and nth cousin is basically arbitrary. (Although obviously there is logic in making the distinction as well as in omitting it.)

Arbitrary? You have the same parents with sibling; with cousin you share only one of the two pairs of grandparents.

Actually that's often but not always true -

    brother b1 and sister s1 from family 1, with parents g1
    brother b2 and sister s2 from family 2, with parents g2
    s1 has child x with b2 - x has grandparents g1, g2
    s2 has child y with b1 - y has grandparents g1, g2
x and y are cousins, and also share the same 2 pairs of grandparents :-)

It can get even more fun!

If instead of two brothers marrying two sisters, you have two brothers marrying two first cousins, like so...

    b1 and b2 are brothers
    c1 and c2 are first cousins
    b1 and c1 marry and have child x
    b2 and c2 marry and have child y
... then x and y are both first and second cousins (and their children are second + third cousins, etc).

Those are "double first cousins". I even have some triple cousins in my tree, where three siblings from one family married three siblings from another family.

Agreed: in the case of siblings you share all ancestors; with cousins only some. In that way the distinction makes sense. The other way to look at it though is that with siblings your common ancestor is one generation up. With first cousins, it's two. With second, it's three. So it's the same thing, just a matter of degree.

Thank you for being sane.

Russians are decent people, it seems. Is the 2nd-uncle terminology widespread in Russia too?

Also good because it means you are your own 0th brother which makes sense. In the western version you are your own -1st cousin :(

No, you don't. You don't call a son of your first-cousin your second-cousin. You call him a second nephew I think.

No, stop that removed madness!

Worse even, the "once removed" notation has no notion of direction, so it's inherently ambiguous. I'm also pretty sure that less half of the people I hear using it know what it means (or tries to mean).

This got me confused. You actually mean people who confuse "second niece" (i.e. your cousin's son) with "second cousin". Is that usage common in english? The daughters of cousins are second cousins,no?

Isn't the term "uncle" relatively recent? I recall Hamlet referring to his father's brother as his cousin.

You must be very old.

You are hitting the borders where logic and common usage meet.

I am actually surprised that descriptive grammar holds up so well to logic. (There's no a priori reason why descriptive grammar, that describes common usage of language, actually is as mostly compressible to simple rules as it is.)

If there's a clearer and more specific way to speak about something, we should try to use it.

Design of language is a constant trade-off, between ease of remembering, compression (ie giving shorter ways to express more common concepts), fault-tolerance, desire of the speaker to look clever, fashion, ...

And all of us work on the evolution of language every day.

That's how we've always done it.

* Brother of father is uncle. Son of uncle is cousin. Son of son of uncle is second cousin.

* Brother of grandfather is great-uncle. Son of great-uncle is second cousin.

That's exactly what you shouldn't be doing.

Edit: Nvm. I am more confused than I thought.

I've always wondered about this one:

My father's first-cousin-once-removed is what to me?

That depends on which direction the cousin is removed. If a generation above your father, it is your first cousin twice removed. If a generation below, it is your second cousin.

Your second cousin if you share the same great-grandparents.

Edit: Ugh, this gets confusing. I was mistaken. I'd originally included the once-removed, but that appears to be incorrect. Or I'm still mistaken. :)

A first cousin once-removed signifies one person's grandparent is the other's great-grandparent.

Perhaps this cousin chart would help: https://en.m.wikipedia.org/wiki/Cousin#Relationship_charts

Just plot yourself and the cousin-in-question by where your shared nth-grandparent lies.

You are a (1,0)-child to your father (who is a (0,1)-parent to you). Your father is either (2,3)-cousin or (3,2)-cousin to the other person. It is ambiguous from the terminology. So you are either (3,3)-cousin or (4,2)-cousin to them. That is second cousin for the former and first cousin twice removed for the latter.

I think, if your father's cousin-once-removed is a generation below him, then he/she is your first-cousin. While a generate above you father would signal first-cousin-twice-removed...


In the first case he/she would be your second cousin, not first.

Depends on the direction removed?

You get mad? Really? Why?

Where our family is from the priests wouldn't allow marriage between 6th cousins. My grandfather was 6th cousins three times removed from my grandmother. (so she was 9 generations away from common ancestors with him) They had to get written permission from the bishop to get married.

The Church worked very deliberately over centuries to reduce the influence of families / clans, in some places more successfully than others. It all revolves around inheritance rights and accumulated power. (Also in some cases the Church could collect money by charging for exemptions.)


Sounds like they basically penalized record keeping ...

Ah, it was probably the Church who was keeping the records in the first place.

The beauty of selective enforcement. Dig deep enough into your ecclesiastical data-monopoly and you can veto just about any marriage at will. It never was the same again once laymen started to read and write.

Yes, it was the Franciscans who were a huge influence and kept record of these things.

Most people would remember relations as far as great-grandparents and relations to families/family friends that they knew. Literacy was pretty high in the region early on as well, but people continued to rely on the church for recordkeeping.

Through induction, you can also say that your sibling is your nilth (0th) cousin, and your identical twin is your negative-first cousin. That makes aunt or uncle a nilth cousin once removed, and a great aunt or great uncle a nilth cousin twice removed. Your parents are negative-first cousins once removed.

If this sounds ridiculous, that's because it is, as a natural consequence of the ridiculous nomenclature.

It would be far less confusing to just insert an unordered pair of numbers for both individuals' genetic distance from their common ancestor. So instead of a first cousin once removed, you would have a (2,3)-cousin. Identical twins would be (0,0), parents would be (0,1), ordinary siblings (1,1), aunts and uncles (1,2), and so on. A fourth cousin would be (5,5).

But that doesn't account for half-siblings, so it would be inadequate for some family relationships.

I used to really struggle with those types of diagrams. Like, they make sense on their own, but it's hard to reason about the patterns with them; the relationships (heh) between each diagram aren't clear.

I much prefer the square/diamond type diagram that's further down in the article. It seems like black magic at first, but if you stop and think about it for a bit, once you understand it, is crystal clear.

I guess it's about short-term or long-term ease of understanding.

Let's calculate. I have a pair parents, 2 pairs grandparents, 4 pairs of great grandparents, 8 pairs great-great grandparents, and 16 pairs great-great-great grandparents.

How to estimate the number of fourth cousins?

Wow, takes me way back to an undergrad programming assignment to take a family tree and compute the degree and "removedness" of any two cousins.

It is mentioned in some comments of comments further down but Wolfram Alpha has some great family tree generation.


Also, its grand-uncle (not great-uncle). You don't have a great-mother do you? Its a grandmother. Thus granduncle.

The lead author, Nicholas Christakis, is the man who was reviled by some students at Yale during the Halloween costume debacle: http://www.theatlantic.com/politics/archive/2015/11/the-new-....

Thanks for reposting that article. I swear I'm starting to feel like an old man "back in my day, vigorous intellectual disagreement and debate was the point of living on campus during college"

Back in my day, vigorous intellectual disagreement and debate was the point of living on campus during college

Well they've sure fixed that, haven't they.

I read Erica's infamous email without any knowledge of the situation, and only a vague impression that she was the wrong end of some campus non-event. The letter was so well-written and thoughtful! The key line, that she does not trust herself to police Halloween, was so effective.

Then I watched the video of the children yelling and cursing at Nicholas. Yes, they fixed that all right.

[TheLarch proffers curmudgeon fist bump]

I hope you're not suggesting that has any bearing on the quality of the paper?

Not sure if you are speculating that I am a supporter or detractor of his. My only impression of the man up until now was that I thought he and his wife conducted themselves with grace and forebearance during the Halloween fiasco. I find this research fascinating.

I don't think there's any implication of that. It's just a nice piece of trivia.

From my reading, the article in question gives me a complimentary view of the author, and a less complimentary view of those who reviled him.

Where I grew up, it's a pretty good chance all my friends were fourth or fifth cousins. Small population + limited outbreeding = family hedges, instead of family trees.

There were kids in my grade who couldn't date in town because all the girls were their first or second cousins...

> second cousins

Didn't stop my great grandparents :) My mom's side is Mennonite, which is also a very tight knit community. When my grandma sends random pictures from in and around Goshen, Indiana, my wife has commented multiple times "whoa that guy in the background really looks like you!"

Really not an issue with second cousins. Second cousins are genetically different enough that issues with the children are just barely more common in non-related couples.

Yep. That's the kind of thing you look up at a young age when you discover you're the recent product of second cousins. Some interesting quotes from the "Cousin Marriage" Wikipedia article:

"According to Professor Robin Fox of Rutgers University, it is likely that 80% of all marriages in history may have been between second cousins or closer."

"Worldwide, more than 10% of marriages is between first and second cousins."

"In some countries it is seen as incestuous and is legally prohibited: it is banned in China and Taiwan, the majority of U.S. states, North Korea and South Korea."


Einsten, Darwin, and Giuliani all married their first cousins, from what I understand.

Well Darwin had 10 children, but only 9 grandchildren. So maybe it didn't turn out so well. Not from a personal or moral perspective mind, just from strictly Darwinian perspective.

That is less interesting, in the context of inbreeding, than any of them being products of first cousin marriage.

I think Roentgen, discoverer of x-rays, was the product of first cousins.

(I bet Wikipedia has a list of famous persons being children of first cousins.)

Darwin's family history is fascinating -- the intertwining with the Wedgewoods (as you note, Charles and Emma were first cousins), but doubtless exacerbated by the frequent first-cousin marriages in Emma Wedgewood's recent ancestry.

Darwin was aware of the risks of inbreeding, and this marriage in particular, expressing those concerns in various writings.

They had 9 or 10 children, IIRC, with 3 or 4 of them dying in childhood, and only a couple going on to produce a further generation. (Not so uncommon these days, but at the time I believe this was quite noteworthy.)

Such a rate of childhood death would be high even for sibling parents. So perhaps there was something else going on.

> Such a rate of childhood death would be high even for sibling parents.

Really? In the mid-19th century?

https://ourworldindata.org/child-mortality/ says "in 18th century Sweden every third child died, and in 19th century Germany every second child died" (that's before the age of 5; the usual definition of child mortality). The "England and Wales" chart on that site shows that in the mid-1800s child mortality was about 250-300 per 1000.

So out of 10 children you would expect 2-3 to die before reaching age 5 at the time.

If you look at https://en.wikipedia.org/wiki/Charles_Darwin#Children there were 10 children. Their ages at death are:

74, 10, 1 month, 84, 67, 78, 77, 93, 77, 18 months.

So two deaths before age 5, one death at 10, the rest living to perfectly reasonable ages. Doesn't seem at all unreasonable for the time period.

Thanks, didn't at all realize how bad it used to be :O Even today it seems to be much worse than I'd naively assume.

Yeah, historically people had lots of kids not least because lots of them would not survive...

As for today, child mortality in developed countries is well less than 1%. And most of that is infant mortality (death before age 1). For example, http://apps.who.int/gho/data/view.main.CM1320R (sorry, somewhat slow) shows that in the US in 2015 infant mortality was 5.6 per 1000, while child mortality was 6.5 per 1000. Neonatal mortality (death within 4 weeks of birth) was 3.6 per 1000.

And a lot of that is preterm births; for full-term births the US rate of infant mortality is closer to 2.5 according to http://www.webmd.com/baby/news/20091103/preemies-raise-us-in...

(Insert here rant about how different countries report some of these numbers differently, with some counting a 21-week birth followed by death a day later as a miscarriage, some counting it as a stillbirth, and some counting it as a live baby that died. As the mortality numbers drop these edge cases matter more and more. Obviously back when child mortality was in the mid-double-digit percentages these edge cases were not really important.)

What was your naive assumption about child mortality rates, if I might ask?

I don't remember having a concrete number in my mind. I guess I'd assume .1% for today. Had a picture of it as "something that's very tragic and basically doesn't happen anymore". While .5% puts it into the "not likely but might happen to you" range.

And as for a century and two ago I'd be waaaaaaay off base. Probably 10% or even 5%. It's hard to say in the hindsight. Now it seems so obvious and makes you feel stupid.

Maybe they were trying to breed super-geniuses.

A dude with whom I went to elementary school married his first cousin here in USA. This was in a red/"statute bans" state by the map at your link, but I never heard they had any problems from it.

From a genetic perspective, even occasional first-cousin marriage is not really a problem. The problems start when you have several generations of cousin and sibling marriages, allowing homozygous recessive alleles to concentrate.

What jacobolus said. First cousins are also genetically different enough that issues with the children are just barely more common than in unrelated couples. (The relative risk adjustment is quite high, but the absolute risk is still low.)

If marrying your first cousin is a culturally accepted practice, it happens all the time and people get much more inbred than you might expect from looking at, or calculating from, a stylized 8-person cousin marriage family tree. And that goes for second-cousin marriages too, to a lesser degree.

But first-cousin marriages generation after generation are not a great idea, as happened in various royal houses of Europe in order to make sure both parents were of noble blood. In fact, it has been estimated that the last Hapsburg ruler of Spain, Charles II, ended up with more homozygous alleles than someone who was the offspring of siblings would. And he had numerous physical and mental problems that were probably the result of it.

Your reply starts with "but", but I don't see the contrast with anything I said? My comment specifically notes that cousin marriage as a recurring practice causes much bigger problems than a single case of cousin marriage in isolation. That note is more than half of the entire comment.

Fun fact: people like to present Charles II as the inevitable result of ongoing inbreeding, but he was noticeably less inbred than more competent historical rulers. Amenhotep I and his great wife had, between them, two parents, two grandparents, and two great-grandparents. Unsurprisingly, he and his great wife turned out not to produce any viable children. Unsurprisingly, that line also experienced early death outside of combat. But surprisingly, they don't seem to have been plagued by mental difficulties at all; as best we can tell from the record, they were very strong kings.

It wasn't first-cousin marriages that screwed up the mainline Habsburgs; it was generation after generation of uncle-niece marriages that did it in. The current branch of the family (Habsburg-Lorraine/Hohenberg) was fortunate enough to avoid that.

This is a dataset designed to study genetics in a cohort of mostly white people from Framingham, MA. How can anyone claim to be able to draw conclusions about the genetics of friendship from this cohort? This is such a biased dataset I can't believe this got published.

For the record, I am Indian, my best friend growing up was Italian, my current best friends are a Russian Jew, a Scotch Irish mix from Woburn, and a Canadian of some uncertain European temperament. I have never had a best friend even close to being my fourth cousin.

They explicitly call this out and apply population stratification later in the paper.

Yeah, which means the extensibility of these claims is exactly as good as those corrections, which can't possibly hope to model the missing information (the actual genetic distribution of friends).

Given that the US is a lot more racially heterogenous than the majority of the world (where the average person would have friends of a closer genetic makeup), I would bet that if anything these results are skewed the other way.

    > Given that the US is a lot more racially heterogenous 
The US? Sure, but this isn't about the US.

The population chosen (or available) for the study does not reflect that diversity.


    > The Original Cohort of the Framingham Heart Study consisted of 5,209 respondents
    > of a random sample of 2/3 of the adult population of Framingham, Massachusetts
So I don't understand why you point to diversity in some wider but not included group to reason about results based on the much more limited one.

Stratification doesn't help much - it doesn't generate missing data, it still is based on that limited population.

The study isn't "wrong" of course, it clearly states what data it is based on and what methods they employed. If there's anything wrong it's the interpretation by others. This is merely a hint "maybe worth having a closer look at this", it isn't meant to be used to draw any final conclusions from. Papers like this are for "internal use", for other researchers in the field, it should never go to the wider media. It's like a programmer showing their very first lines of code for a new idea, and then trying to draw conclusions about the quality of the final software to be released five years later, written by different people in a different programming language. Bad example, because here at least you already know what it will be about while in the study this remains open, so I reframed it to be about "(software) quality".

I used to live in Malden, and IIRC Framingham and the other suburbs were pretty diverse. That's what I was basing my comment on.

Of course, my personal bubble could have skewed this -- looking it up it seems like Malden is more diverse than Framingham, but Framingham seems to still be close enough to the overall distribution in the US. Not the same of course.


> The study isn't "wrong" of course, it clearly states what data it is based on and what methods they employed. If there's anything wrong it's the interpretation by others. This is merely a hint "maybe worth having a closer look at this"

Right, that's all I'm really talking about -- the paper is very responsible about possible bias, and tries to correct it (as you said, that's not completely possible), very far from "I can't believe this got published" territory as the original commenter was mentioning.

Okay, here is what you wrote:

    > Given that the US is a lot more racially heterogenous than the majority of the world
"The US". You didn't say "Framingham". You know, it's really a PITA to have discussions with someone who can't just say "I made a mistake, I edited my comment" or something like that and instead try anything else.

Sure, I made a mistake. I was using prior knowledge of Framingham/the region that I didn't spell out in my first comment. I should have done that, but I was lazy and it didn't occur to me. Happy? I spelled it out in the next comment to explain the basis of the previous one, which I felt was sufficient. Evidently it wasn't; because you want explicit admission of fault. Here you go.

The problem is all they're measuring is the genetics of this locality, or any locality. You acquire your friends mostly through geographical proximity; in most places, the people nearest you are going to have a certain level of relatedness.

But this has less to do with friendship and more to do with geography; they might have achieved a similar result by comparing people to their neighbors.

Exactly. These results would make sense in almost every part of the world, except the US.

The genes that you get from your ethnicity are a small fraction of your overall genome. There are tons of other genes that affect things like your height, your interest in music, etc, that could strongly affect your friend selection.

And I got those in some other way than my ancestry...?

I'm not sure you understand the whole genetics thing.

Could it just be more common for people who are in the same social group to be in the same ethnic group, and maybe that explains most of the genetic similarity they saw, rather than necessarily proving some kind of fitness advantage or something? Probably because often your friends are from the same neighborhood.

The genetic similarity here is estimated within the cohort; the Framingham cohort is by design ethnically homongeous to try to eliminate that sort of population structure confound. This way, the homophily is not picking up on the obvious stuff like ethnic groups. If they studied people from multiple ethnic groups, the results would be trivial and uninteresting. (This is why astazangasta's criticism in another comment is so amusing - this is meaningful because the sample is so 'biased'. This also holds for all the other studies done on Framingham.) But because only one highly homogeneous sample is studied, the chance genetic similarities of friends aren't due to just similar ethnic backgrounds, but are being caused by the genetic influence on things like SES and personality and intelligence and religiosity and hobbies and things like that. These similarities would probably also hold when considering a more unusual and cosmopolitan group, but it would be difficult to spot the increased similarity on a genome-wide basis because of all the racial differences in genomes (most of which would be nonfunctional and irrelevant to anything).

They only apply population stratification from Figure 2 including onwards:

>The results so far do not control for population stratification because we wanted to characterize overall similarity. However, it is important to remember that some of the similarity in genotypes can be explained by simple assortment into relationships with people who have the same ancestral background. The Framingham Heart Study is composed of mostly whites (e.g., of Italian descent), so it is possible that a simple preference for ethnically similar others could explain the results in Fig. 1. However, in the following results, we applied strict controls for population stratification to ensure that any correlation we observed was not due to such a process.

I don't understand why they did not do this for Figure 1 (or why they do not show that figure) - I assume that the difference disappeared, but who knows.

I just realized that this paper is from 2014, first published on arxiv in 2013. I can't find any study replicating it in the 34 citations since so I would be careful (but this type of dataset for replication is hard to come by) https://scholar.google.com.au/scholar?cites=7301900347564089...

* fourth cousins genetically as diverse as random strangers would be a better wording

the current title has implications not yet rigorously tested and people is already looking into selection bias to explain correlation where probably there's none.

> fourth cousins genetically as diverse as random strangers would be a better wording

That is not the same at all. From the abstract:

> More than any other species, humans form social ties to individuals who are neither kin nor mates, and these ties tend to be with similar people.

They specifically tested friends to include the general preference of friends to be similar.

Related: https://www.sciencedaily.com/releases/2008/02/080207140855.h...

Third cousins are most fertile.

So, marrying friend is a good idea from fertility point of view.

"Fertility" does not necessarily mean "fit offspring", but your point stands.

Define "fit offspring".

I consider "offspring that has many offsprings" as one that fits definition "fit offspring". If you read the article you would know that third cousins' couples have more grandsons. Thus, third cousins direct offsprings are... more fit than others!

There's a pretty good CGP Grey video that explains family trees and what fourth cousins are:


The main finding from my perspective is that we can score and rank friendship likeliness and see signal in a hold out dataset.

I can almost hear Facebook clamoring to offer free genotyping.

The dating world is already experimenting. (e.g. http://www.genepartner.com/)

How many Americans know any fourth cousins? In the village from which two great grandparents emigrated, I have met some third cousins, some at least twice removed, and here in the US I have met second cousins once removed. For what it's worth, it would take a very sharp eye, and maybe an unduly imaginative one, to spot family resemblances between the third cousins and me.

I know plenty, due to both an active family reunion group and due to genealogical research. It can be pretty fun learning about your ancestors.

Most people with European ancestry are 10th or 11th cousins to each other based upon how every US president is related to every other. This includes the current President who is half Eoropean.

> Most people with European ancestry are 10th or 11th cousins to each other based upon how every US president is related to every other.

"The people who have been elected President of the United States" are not a representative sample of "people currently alive with European ancestry" (or even a nonrepresentative subset of that set) such that generalizations about relations between members of the latter class could be drawn from the relations between members of the former class.

And even if they were, strong conclusions can't really be drawn from an N=44 sample.

2 ^ 11 = 2048 great ... grandparents. However, the top row only counts as one set. Thus, at most 1,024 couples. 10 generations down with 3 kids a generation is 59,049. Assuming zero deaths and zero intermingling that's 60,466,176.

So, your going to need very large family sizes for that to work out once you account for deaths without children or intermingling. France averaged 4.5 kids a couple in 1800 so I don't think this math works.

Its not math, but exhaustive geneologies by experts who've tracked every US President as far back as Saxon England. These emperical results constrain theoretical calculations.

Your assuming US Presidents are a representative sample. That seems highly dubious. I mean one is the child of another. More importantly 11th century is much more than 11 generations back. Go to 20 generations and include people at different generations then sure.

Can it be interpreted that friends are as similar as random people?

No. The article mentions a number of reasons why friends can be (and are) genetically closer than random people.

Assuming you have 44,000 genes (a copy from each parent) and random recombination each generation, then some of your ancestors will have stoped contributing genes by 16 generations (400 years). These assumptions arent perfect, but givebyou a sense of what happens.

(People have far fewer than 2^N ancestors due to distant cousin inbreeding) (Genetic recombination is not random, but chunky.)

This is not necessarily accurate as a fair amount of what we think of as Junk DNA is actually used. And a large chunk of DNA is devoted to basic cellular function which fails if it's modified.

Very weak correlations. Spun as a hypothesis-positive result.

so what would be the best way to increase genetic diversity?

Why are you under the impression that it needs to be increased?

Why would we need that. Assuming we 've gotten over our survival issues a looong time ago, what would be the benefit other than weirdly looking humans?

Study abroad!

Doesn't 23andme "identify" fourth cousins?

Haven't read the text yet, but the title remembered me of the Hungarian psychiatrist Leopold Szondi.

in other words, we pick friends from the same ethnic group

I live in Toronto, and frankly I doubt my Panjabi, Sri Lankan, Chinese, and Korean friends are as genetically similar as my fourth cousins.

It could be that you share certain alleles at a much higher rate than expected by chance.

That said, if the study is working off the Framingham data, I do wonder how general a conclusion it is...

Pretty sure my Thai best friend is more dissimilar to me than a fourth cousin.

unless you are thai yourself? are we supposed to presume that everyone is not-thai on this site?

Fair enough. I'm not even Asian.

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