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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

#21

Post by srtjstjsj »

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?

There's an app for that!

https://www.microsoft.com/en-us/store/apps/cousinosity/9nblg...

Re: Friends are as genetically similar as fourth cousins

#22

Post by a_bonobo »

aab0 wrote: post #17
ilaksh wrote: post #4

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…

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...

Re: Friends are as genetically similar as fourth cousins

#23

Post by dietrichepp »

ironrabbit wrote: post #20
dietrichepp wrote: post #19

Earlier quoted context omitted.

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

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

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".

Re: Friends are as genetically similar as fourth cousins

#24

Post by rat87 »

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?

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.

Re: Friends are as genetically similar as fourth cousins

#25

Post by Throwaway23412 »

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?

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

Re: Friends are as genetically similar as fourth cousins

#26

Post by milesskorpen »

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.

Sounds like they basically penalized record keeping ...

Re: Friends are as genetically similar as fourth cousins

#27

Post by mod »

Throwaway23412 wrote: post #25
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?

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?

Re: Friends are as genetically similar as fourth cousins

#28

Post by Manishearth »

astazangasta wrote: post #8

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 C…

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

Re: Friends are as genetically similar as fourth cousins

#29

Post by jacobolus »

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.

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.)

https://en.wikipedia.org/wiki/Consanguinity#Religious_and_tr...

Re: Friends are as genetically similar as fourth cousins

#30

Post by m_myers »

mod wrote: post #27
Throwaway23412 wrote: post #25

Earlier quoted context omitted.

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.
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