The Bible says everyone is drawn out and enticed by their own desires.
The desires become fertile and give birth to sin.
If we didn't have a reproductive systems we wouldn't have a desire for sex.
If we didn't have a digestive system we wouldn't have a desire for food.
If we didn't have muscles we wouldn't have a desire for exercise and movement.
If we didn't have a brain and nervous system we wouldn't have a "self" or "selfishness".
Sin is moral badness where in the process of satisfying your own desires you cause unnecessary harm. The Bible calls it "that superfluous thing" ie beyond what is necessary.
There seems to be a factor of greed or excess to sin.
People are perfectly equipped to do-evil without any help from a personal d--evil.