If of one person today every previous generation had a unique pair of ancestral parents then go back 80 generations that’s 2^80^ of people had to exist during that 80th generation back. That’s more than 1.2 septillion so a one with 24 zeros. So that’s impossible that’s more people than have existed in history. Meaning that inbreeding has happened in everyone’s family tree. So lots of distant cousin marriages. But unfortunately also some fucked up shit like some of your ancestor’s parents are brother and sister or father and daughter. So if you follow one of your paternal lines back the number of dads is less than the number of mothers.