[js1138]

That's like asking if ant holes are natural or artificial. The word "artificial" is generally understood to mean, done by humans, or by lifeforms with at least a similar level of intelligence and sentience.

That is the general usage of the term, but humans are part of the natural world.

[inquest]

That just depends on the definition you use. Used overbroadly, the word is meaningless, because it means everything. A word that means everything ends up meaning nothing, because there's no differentiation.