We Are Our Brother's Keeper: Are All Men Cousins? And Is This The Root Of Prejudice?

Many of you already know the following concepts.  Humans intuit a sense of community and family with those with whom they are related.  This has been confirmed in study after study, on child abuse, on ingroup-outgroup dynamics, and on racial prejudices.

The percentages of relatedness to trigger that feeling of kinship need not be large.  As the following chart shows, many of us have folks over to Thanksgiving dinner with whom we only have 1-3% of identical DNA with.  But that identical DNA is hugely significant.  It's identical.  And that of course makes one much more "related" than this "we share most DNA with all humans and even chimpanzees."  Indeed, it's the margins that seem to count.  And again, studies on stepfathers in particular, have confirmed this time and time again.

Parent / Child
Full Sibling       50%

Grandparent / Grandchild Aunt / Uncle Niece / Nephew Half Sibling	25%
1st Cousin	12.5%
1st Cousin once removed	6.25%
2nd Cousin	3.13%
2nd Cousin once removed	1.5%
3rd Cousin	0.78%

The weird quality of the Y-Chromosome makes what I am about to post intriguing:

A human genome, including the X and Y chromosomes, is about 3771 cM long.

The Y Chromosome makes up about 2% of that, by length, and about 1% by SNPs. 

Because men in certain haplogroups have IDENTICAL Y-Chromosomes (except for tiny combining parts), and because unlike the rest of DNA, those genes are passed on IDENTICALLY, then all men in the same haplogroup share as much DNA as, say, 2nd Cousins Once Removed.

Could this be the explanation why, for example, Western European males, which do not have much Y-chromosome diversity, exhibit a powerful ingroup dynamic with each other?

Fascinating, to be sure.

Calculating Matches on Gedmatch: Why CentiMorgans (cM) are more important than SNPs

I have discovered that very very very few people know this, so it is worth posting.

The different testing companies, 23andme, Ancestry, FTDNA, etc. all test slightly different SNPs.  In other words, the "points" on the genome, the "genes" that are tested vary from company to company.

I have seen some people on Gedmatch dismiss a match because "it doesn't have enough SNPs."  Or because "it's not above the SNP threshold."

Gedmatch itself uses a 7 cM and 700 SNPs match to qualify someone as a cousin.

The SNP part is faulty thinking.

Because the testing companies don't test the same SNPs, you can have long stretches that match with a low number of SNPs.

Case in point: Someone who tested on 23andme like I did matched me for 10.0 cM and 1024 SNPs.  That same person on FTNDA matched me for 10.0 cM but just 510 SNPs.  FTDNA tested half of the SNPs that 23andme did (or half of the same set). 

This is key to grasp.  Expect closer matches to you on Gedmatch if your kits start with the same letter (i.e. M for 23andme, F for FTDNA, and A for Ancestry.)  DO NOT DISMISS LOW SNP MATCHES.