But surely people do make intelligent decisions when choosing partners. It's not just instinct is it?
The sense in which they are designing their descendants when they do so seems rather tenuous. I might, I suppose, choose a red-haired wife in the hope (for whatever reason) of having red-haired children, but can it be said that in that case I designed my children? It seems an odd use of the word.
But intelligence was involved in the survival of the "red hair genetics" (forgive my terminology)?
If someone has a good reason for wanting his offspring to have red hair, then marrying a red-haired woman would be an intelligent step to take towards that goal.