I just made a theory and it's crazy. I think we're all brothers/sisters. Like when the first humans were born there had to been only 2 right? Even if there was 4 we would still all be related. Let's just say there was 2 humans in the beginning and like they reproduced but the kids who are they reproducing with? It has to been incest so this means we're all brothers/sisters. If there was 4 humans it would be less incest maybe but we would still all be related.