Well it does appear that Eve was tempted....which until satan was thrown out of heaven that wasn’t possible....so our sinful nature came about after the fall wouldn’t you say?
Well, we must have had the capacity to sin in order to commit the first sin, but the Bible tells us that once the first sin was committed, our fundamental nature changed for the worse.
I think in our first state, we could choose to sin or not sin, but now we can’t (freely at least, without Christ) choose not to sin.