The craziest thing to me is that this diagram, which only represents the last 200 years of your ancestry, contains 127 romantic relationships, each involving at least one critical sex moment and most of them probably involving deep love. You’re the product of 127 romances, just in the last 200 years alone.
. . .
So in this frenzy of procreation we’re all a part of, what’s the deal with our relation to the other people on this Earth today?
The simplest way to think about it is that every stranger in the world is a cousin of yours, and the only question is how distant a cousin they are. The degree of cousin (first, second, etc.) is just a way of referring to how far you have to go back before you get to a common ancestor. For first cousins, you only have to go back two generations to hit your common grandparents. For second cousins, you have to go back three generations to your common great-grandparents. For fifth cousins, you’d have to go back six generations until you arrive at your common pair of great-great-great-great-grandparents.
. . .
In any case, you have hundreds if not thousands of third and fourth cousins and you’re probably friends with some of them without realizing it—you might even be dating one of them.
The other way to look at this is from the top down and see how quickly the distance of relation is magnified as generations move down—while you and your sibling grew up in the same house, your kids will be cousins who might or might not be friends and your grandkids might barely know each other. When it comes to your and your sibling’s great-grandkids, it’s likely they won’t ever meet, and your great-great-grandkids might be best friends with each other and will never realize that their great-great-grandparents were siblings.