He was never really human; he was just programmed to protect humans. But as the Roidmudes evolve, their emotions become more human-like. The same is happening to Brain (001 said it's significant that Brain has reached the stage of being able to feel jealousy) but while he is becoming angry and destructive because of it, Chase is becoming kinder and learning to form relationships with humans. Heart is more advanced than either of them in that he realised by himself that letting Chase go would be the compassionate thing to do; and Medic is less advanced in that she so far doesn't show any signs of genuinely caring for anyone.