But we don't. What if they only have sons? It is an interesting question though. Assuming that we could par people, and realizing that way less men are needed than women, maybe 2-3 men (1 for back up) and 8 women would do the job. This way inbreeding could be avoided for at least 2 generations and cousins marrying didn't seem to be a huge problem in the past.... Here is the coupling: Men are called A and B, women 1-8 Man A fathers kids with 1-4 women, who later breed kids from Man B and women 5-8 kids. For faster population we throw in a more complicated version too, where both men fathers kids with all women (but we assume fatherhood can be established) and the kids marry first the unrelated kids. Then down the line they will try to par off the less related kids.