"We do have evolutionary theory. The nature spirits resist change, but not quite so punishingly on evolutionary timescales. I thought you meant, like, beavers invading a new area. They get pushed back, but not completely exterminated. And spirits can die or new ones form, yes."

"I wonder if they've had much macro effect on - things - is your world an Earth?"

"Yeah, that's what it's called?"

"About how many nature spirits are there?"

"Hm... I'd say, one every hundred or two kilometers? Much less dense in the ocean and a bit less dense in barren places like deserts or the arctic. Probably ten thousand is the right order of magnitude, at least."

"Do they jointly cover the planet or are there gaps?"

"There's some gaps, big gaps turn into a new spirit being born sooner or later, there's some overlapping claims too. There's a river spirit that claims half the rivers and streams in Central America, but the more local spirits also protect those rivers."

"What kills 'em when they die?"

"Too much change in too short a time, like big natural disasters or oil spills, can do it. Magical damage too. Other nature spirits who want to expand. Genies randomly deciding to take out a weak spirit. Monsters attack everything. Spirit bearers, sometimes."

"Is 'magical damage' a natural category?"

"Uh... It's pretty distinct from 'physical damage' if that's what you mean? There's things that only hurt magic and not physical objects?"

"What is magical damage?"

"It's magical damage. Being hit by some hurts like hell if you run on magic but isn't a big deal otherwise? I mean... What's space? It's space. Things can be in it. I don't know."

"Well, like, we don't have this, I'm magical because I can do magic and I can do magic bolt attacks but if I'm damaged it's damage to my body or the rock, or there's gem drain..."

"Well, I suppose you could say it's like pouring into a leaky bottle - the bottle is my total magical power and incoming water is magical damage. If it overflows, you die. If it gets near the top, you become highly emotional and kind of manic and unstable. We can take damage off someone else- Wait, want to try that?"

She holds out her gem.

She touches it with a pointed finger.

"...I can tell there's something there, but there's no damage to pull."

"Oh well."

"Magical damage really sucks, though. You heal best when you sleep, but it also makes for really vivid and memorable dreams. Not always pleasant. That reminds me. Damage to a spirit bearer's body is uncontrollably, rapidly regenerated, in exchange for some amount of magical damage. Can't suppress it."

"- and you'd want to because magical damage sucks so much?"

"Yeah. At least for a little while, to keep the pain managable. Or because you're close to your limit on damage and would rather be missing a hand for a few hours than die."

"I can regenerate from literally nothing left of my body if I have enough charge and my gem's intact."

"Good for you! We can regenerate from nothing too... It's just I wish choosing not to quite yet was an option."

"Well, it's not super optional for us either, if we don't we'll run out of charge. Is why it works that way known?"

"Nope. Monsters seem to work the same way, but nature spirits and genies don't."