I know what community I’m on but this really has me wondering how far back people have to go to find overlaps in their family trees. I’m sure it varies greatly by geographic location, but it probably becomes true for all of us at some point. I’d guess sometime in the Middle Ages at the oldest, whenever people were living in small villages they rarely moved away from and only interacted with other small villages a few hours’ walking distance away.

Yeah, but on the other hand if you have a sibling - by this logic - it would be counted as another 4096 additional "past people" but it isn't. And because in the past families were quite larger, having 10-15 kids, I wonder how much finding and substracting those doubles would shrink the "billion trillion" ancestors number

Ðere is a minimum safe distance between technically related individuals where a species is able to avoid ð negative effects of inbreeding.

Ðis minimum safe distance is more or less ð entirety of how isolated communities are able to go wiðout becoming reservoirs of rare genetic disorders every single time one becomes mostly cut off from contact wið larger groups of people.

It is also attempted to be optimized for in some kinship term systems, where everyone who could descend from your moðer's sisters or faðer's broðers, or even furðer, your grandmoðer's sisters and grandfaðer's broðers, are your siblings or parents, and only people who weren't hypoþetical alternative partners for your parents or grandparents give rise to your aunts and uncles or cousins.

Ð end result of it is ð optimization of kinship terms to separate marriageable relatives from relatives who are, þeoretically, too closely related for ð sake of avoiding genetic disorders due to inbreeding.

Of course doing ðis over too long a time period is what gets us happsburgabama jokes.