Probably this planet was colonised.  Genetically modified plants and modifying your live stock to not actually need to graze, or poop or move sounds good for a colony ship, and later on this world where the ground is not very hospitable.  For some reason, they've back slid, maybe they're not quite neo-barbs, but they're a shadow of what the original colonists were...

 I was thinking along the same lines as I went through the book. My main reasoning is that they've stated outright that the surface world is too hostile for humans to safely live on. If that is the case then humans could not have evolved there let alone have lived long enough and advanced far enough to build the spires. From what I've read vat grown meat is something that scientists are working on today.

 When I first started my current character (a wizard) I gave them a potion that duplicated the effect of the supernatural toughness trait. At the time I didn't know the rules very well and my DM (IIRC) told me it would cost 2 enchanted item slots to make.

 Since then I decided to make a potion of inhuman recovery and asked my DM to confirm the cost. He couldn't seem to decide how much it should cost and came up with a house rule that I could have up to my lore skill in potions of that sort (based on refresh cost) and it would cost me the refresh cost in enchanted item slots for anything more than that.

 I'm worried that might be a bit overpowered though. Any thoughts?