Around the early 1800s there were 128 random strangers on Earth, each of whose genes makes up 1/128 of you. Some prob. knew each other and had no idea they'd share a common descendant. There are 127 critical sex moments in this chart. If just 1 doesn't happen you never exist. 1/5 
Of course if you keep going, things quickly get hectic. In the mid-1600s, you've got over 4,000 ancestors roaming the Earth. Some of them probably fucking hated each other. Also, now you're relying on 4,095 times people banged—if only 4,094 had happened, you wouldn't exist. 2/5
Keep going with this and you reach a weird contradiction. How is this explained? "Pedigree collapse," a euphemism for a whole lot of incest. Fun fact: 80% of all people who have ever lived have been born to parents who were second cousins or closer. 3/5
Cousins gets weird too. 1st cousins share a set of grandparents. 2nd cousins share a set of great-grandparents. And so on. This number quickly balloons out, esp when people have a lot of kids. Everyone on Earth is 50th cousins or closer. We really are all one big family 4/5
Full post here: waitbutwhy.com/2014/01/your-f… 5/5
