I was reading the other day where the producers have said that the modern Hosts are essentially biological machines with the exception of the "pearl."
Well, they're better designed - stronger, more durable, less easily incapacitated by pain - and it's hard to imagine how complex the interface between their nerves and the pearl must be.
Plus, we've seen that whatever constitutes "biology" is constructed in a kind of high-tech small manufacturing process involving something like 3D printers, etc rather than grown from cells.