Males without “certainty of paternity” are unlikely to stick around to pair-bond with a female and help raise the kids. Male birds tend to have high certainty of paternity, but male mammals are rarely certain at all. As a result, male mammals tend to abandon mates and offspring when—if they could just be confident of their paternity—selection would clearly favor their sticking around to help. Mammals have a harder time evolving stable monogamy even though it is, in most regards, the superior mating system.
