We can experiment putting a big poster of the handsome milk man next door, showing six packs, in front of our wives when we mate. Then we can check what percentage of our children somehow look more like him. Alternatively we can also show pics of the young nubile school girls in front of the husbands and see how the school girls’ babies look like.

It only works if what you see actually change your mates. It doesn’t work if you just mate with the same mate and see different things.