I would point out the other component to this, which is that the ideal structure should be what rewards the group, not the individual. So some people might be m

I would point out the other component to this, which is that the ideal structure should be what rewards the group, not the individual. So some people might be most suited as an individual to mate with many partners, but that would need to fall someplace within the larger hierarchy of their social suitability, in which case an absent or unavailable father is not ideal (children do objectively - although not universally - worse on average without their fathers). In that instance, whatever they are personally inclined to do is actually harmful to the broader group, meaning they should be given a compensatory incentive by the group to adopt a less promiscuous lifestyle. In either situation, whether it is natural for them to be monogamous or not, they should end up monogamous for the sake their young. So we have to look at the broader group structure as well.