Puzzle: Say there are only 7 humans and they want to repopulate the Earth. How many women/men should there be to do this most quickly? The rule is no one can have a child with a descendant, a sibling or someone under 20.
You need a minimum of 2 for each sex, otherwise everyone's a half-sibling in generation 2, but you want to maximize women since they're what constrains the birth rate