Is entirely possible, as i already said, that their body reproduce in completely different way. Perhaps at some point a piece of them detach and grow into another member of the species. Or their body start budding, or turn someone else in a simila rbeing as themselves(vampire/zombie style....nobody expect a Mercurypocalypse!). Human, biologically speaking is not the endall of performance in any field(TIL that the reason we have back and neck aches of any sort is our erect posture and HEAVY brain....THANK YOU EVOLUTION....