I think the topic is getting a bit muddled here. Are we talking about couples who can't have children because one or the other is infertile/sterile, or couples

I think the topic is getting a bit muddled here. Are we talking about couples who can't have children because one or the other is infertile/sterile, or couples who could have children with someone else but not one another? I'm not familiar with this latter scenario. A man being sterile is nothing like this algae's situation, as it has nothing to do with "pairing," he's simply unable to produce children with anyone.