I was thinking about how everyone has 2 parents, 4 grandparents, 8 great grandparents, etc etc.
Pretty simple, everyone has 2^(n+2) number of (great)^n grandparents. But what happens when n grows large, say 35 generations back. n = 35 would mean that you would have roughly 137 billion (great)^35 grandparents. 137 billion people is way more people than have ever lived on Earth, so what's going on?