THOUGHT EXPERIMENT: Birds Nests

[Ifreann]

The distinction between artificial and natural was invented by humans to differentiate between things we do and things that happen without our intervention. Our houses are artificial and a bird's nest is natural just because we decided to talk about them differently.

[Aureumterra III]

"Natural" pretty much means not drastically altered by humans, in its common use. For example, a wooden log cabin would be considered natural, but a concrete building would not

[Rusozak]

I think toolmaking is a big distinction. Toolmaking is a major indicator that separates intelligent life from animals. If it requires tools to be constructed, it's not natural. If you can make it with nothing but your bare hands and whatever you can find occurring naturally, it's natural.