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?
You are, to your your first cousin's child, who is your first cousin once-removed, a second cousin once-removed.
Another clearer way to phrase it would be "sons of my first cousin are not my second cousins".
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.
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
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
Russians are decent people, it seems. Is the 2nd-uncle terminology widespread in Russia too?
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.)
And all of us work on the evolution of language every day.
* 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.
My father's first-cousin-once-removed is what to me?
First cousin twice removed, apparently.
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.
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.
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 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.
How to estimate the number of fourth cousins?
Well they've sure fixed that, haven't they.
Then I watched the video of the children yelling and cursing at Nicholas. Yes, they fixed that all right.
There were kids in my grade who couldn't date in town because all the girls were their first or 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!"
"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."
(I bet Wikipedia has a list of famous persons being children of first cousins.)
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.)
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.
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?
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.
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.
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.
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.
> Given that the US is a lot more racially heterogenous
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
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".
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.
> Given that the US is a lot more racially heterogenous than the majority of the world
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.
>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...
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.
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.
Third cousins are most fertile.
So, marrying friend is a good idea from fertility point of view.
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!
I can almost hear Facebook clamoring to offer free genotyping.
"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.
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.
(People have far fewer than 2^N ancestors due to distant cousin inbreeding)
(Genetic recombination is not random, but chunky.)
That said, if the study is working off the Framingham data, I do wonder how general a conclusion it is...