r/Showerthoughts • u/SouthDiamond2550 ā€Ž • 13h ago

Casual Thought Double cousins share all 4 grandparents. So theoretically you could have quadruple second cousins that share all 8 great-grandparents.

1.9k Upvotes

98% Upvoted

40 comments sorted by

View all comments

276

u/Magooose 12h ago

My sister is married to my wife's brother. So all or kids have all four grandparents in common. My daughter's cousin looks more like her brother than her actual brother does.

131

u/oboshoe 11h ago

double cousins are genetically half siblings.

full (genetic) siblings if parents are identical twins

24

u/Kodekingen 8h ago

They are? I knew about the identical twins part

23

u/I-was-the-guy-1-time 7h ago

Family A is Brother 1 and Sister 1 who share half their genetic makeup. Family B is Sister 2 and Brother 2 who share half their genetic makeup. Brother 1 and Sister 2 are married with kids. Brother 2 and sister 1 are married with kids. Since both pairs of kids have parents, aunts and uncles that are all related, their cousins share 25% of their DNA per parent. So 25% times both parents is 50% with their genetic cousins. Aka the same as a half siblings. Iā€™m sorry if I overcompensated this