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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

#111

Post by Retric »

peter303 wrote: post #108

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.

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.

Re: Friends are as genetically similar as fourth cousins

#113

Post by thesz »

amelius wrote: post #100
thesz wrote: post #82

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!

Re: Friends are as genetically similar as fourth cousins

#114

Post by peter303 »

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.)

Re: Friends are as genetically similar as fourth cousins

#115

Post by Retric »

peter303 wrote: post #114

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.

Re: Friends are as genetically similar as fourth cousins

#116

Post by peter303 »

Retric wrote: post #111
peter303 wrote: post #108

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.

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…

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.

Re: Friends are as genetically similar as fourth cousins

#117

Post by bmelton »

sliverstorm wrote: post #104
TheLarch wrote: post #101

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-... .

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

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.

Re: Friends are as genetically similar as fourth cousins

#118

Post by Retric »

peter303 wrote: post #116
Retric wrote: post #111

Earlier quoted context omitted.

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…

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.

Re: Friends are as genetically similar as fourth cousins

#119

Post by bzbarsky »

auganov wrote: post #97
bzbarsky wrote: post #88

Earlier quoted context omitted.

> 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 ab…

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?

Re: Friends are as genetically similar as fourth cousins

#120

Post by kingnothing »

avodonosov wrote: post #66
rat87 wrote: post #24

Earlier quoted context omitted.

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.

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.

First cousin once removed.

https://upload.wikimedia.org/wikipedia/commons/4/4c/Cousin_t...

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