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Friends are as genetically similar as fourth cousins

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Re: Friends are as genetically similar as fourth cousins

#81

Post by delecti »

dietrichepp wrote: post #19
fiatjaf wrote: post #15

Earlier quoted context omitted.

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.

Re: Friends are as genetically similar as fourth cousins

#83

Post by return0 »

fiatjaf wrote: post #15
roninb wrote: post #3

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.referenc…

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?

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?

Re: Friends are as genetically similar as fourth cousins

#87

Post by hx87 »

jhbadger wrote: post #71
thaumasiotes wrote: post #50

Earlier quoted context omitted.

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,…

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…

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.

Re: Friends are as genetically similar as fourth cousins

#88

Post by bzbarsky »

auganov wrote: post #72
Jedd wrote: post #58

Earlier quoted context omitted.

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…

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.

Re: Friends are as genetically similar as fourth cousins

#89

Post by Manishearth »

Noseshine wrote: post #59
Manishearth wrote: post #49

Earlier quoted context omitted.

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. https://www.framinghamheartstudy.org/participants/index.php > 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 un…

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.

shrug

> 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.

Re: Friends are as genetically similar as fourth cousins

#90

Post by Asooka »

skylan_q wrote: post #9
roninb wrote: post #3

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.referenc…

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.

Hold up how does this work? If they're three times removed, then the age difference is something like 50-60 years. Is it a case of a ~75-year-old marrying a ~20-year-old?
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