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
|1st Cousin once removed||6.25%|
|2nd Cousin once removed||1.5%|
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.