Evil is inscrutable. It is irrational. To attempt to "know" evil is an exercise in futility. Those (that includes us) who do evil think we do good. We see "evil", may even call it "evil", but we do it nonetheless because we judge it good for us. It's the definition of insanity.

As DBH would say, there is no ultimate distinction between natural and human evil, since human nature is a natural phenomenon. It has no direct "cause", but is the indirect consequence of imperfection and the brokenness of our world.

Schuon, in great Neoplatonic fashion, understands it as the consequence of the act of Creation or Emanation itself. All manifests God, but never perfectly or fully, or else there wouldn't be a difference between Creation and God...

As he would say "Even paradise had a serpent". The "not-Godness" of creation becomes self destructive when intellect crosses from eternity, the eternal creation, into time. Emanation must reach into nothingness. Such is the nature of creation...

"All Possibility must contain the possibility of its own negation" would be Schuon's explanation. But, because evil is irrational, it is also self consuming. All death is the death of death, and so all must live. The Logic of resurrection is unbeatable.