He was sitting on the levee with four or five of his classmates one fine afternoon, and they realized after some quick calculations that they were ALL cousins!
Mostly third and fourth cousins.
I know who all my third cousins are because I'm from a small Southern town and I'm a genealogy fan. I even know who most of my fourth and fifth cousins are. My great-aunt and her husband were fourth cousins, descended from the same Revolutionary Ancestor (D.A.R. members take note!)
Years ago, I went back to my dad's home town to do a little genealogical research and was referred to a retired physician who was the local authority. We did a little chatting and discovered quite quickly that we were third cousins, both descended from a lady who rejoiced in the name of Victoria Britannia Bale (her daddy was an emigre Englishman and she was born the year Queen Victoria married Prince Albert)!
I have double first cousins. My mother and her sister married my father and his brother. Each couple had six children. My double first cousins all suffer from Marfan Syndrome (only two lived to 30) but neither me or any of my siblings were/are affected.
I can’t say I know any of my 2nd cousins, let alone 3rd or 4th. My family moved though, and are not centered in any small town.