It’s crazy to think how recently you could make a small change, and you would swap out almost all of the human race with people who were never born in this timeline. Consider the fact that you have 2¹ parents, 2² grandparents, 2³ great grandparents, etc. How far back do you need to go before the number of great×n grandparents is bigger than the population of the earth?

2³³ is over 8,000,000. That’s 33 generations. A generation is what, 25 years? That’s like 800 years ago. It is fair to assume that, isolated villages in China or wherever notwithstanding, you are descended from every single person who was alive 800 years ago (who still has living descendants). More so than that, everyone can safely assume the same.

You could swap out almost the entire population of the planet with a wholly different set of humans, if you just cockblocked any of your ancestors 1,000 years ago