Most people probably don’t realize or know that according to the Bible man has two natures, the old man, and the new man.
A lost person, an unbeliever, has only the old nature through his or her physical birth. The moment that individual is being born again through water and the Spirit (John 3:5), he becomes a new creation and has a new nature besides the old nature (II Peter 1:4).
The old nature, controlled by his former way of life, is still there and alive, it doesn’t cease to exist, when one is born again.