I see. Well in general (I cant speak specifically for your system I can only give you a general idea) here the mental health community believe alters are created by children who have been through extreme trauma. It is believed the child feels in danger and uses their mental coping skills to escape when there is no physical escape possible. Children like some adult have very active imaginations and can create their own safety nets in what ever ways, themes, plots that they may need to survive. some children create their safety nets as animals, people or places that enables them to feel safe.

think about what makes you safe, children do the same thing when they feel they are in mortal danger.

children like you can come up with a wide variety and diversity of what gives them a sense of safety. sometimes its another person older or younger than their self sometimes its a male sometimes its female, sometimes its even an animation character they have seen in a movie or on television.

the more this coping skill is used the more real that creation becomes to the child, from their no one really knows what or how those mental safety nets end up taking on lives of their own but they do. At some point those creations start living their own separate lives from the child and continues living separate lives even after the child who created them is grown.

If you google the words DID, Dissociative Identity Disorder, Multiple Personality Disorder you will find a whole load of information about the disorder.

You might also contact someone in a mental health agency near you that can talk with you about this subject. they can tell you what the mental health communities near you understand and believe about this disorder. many different agencies, countries, states and other geographical locale believe many different theories about this disorder and its diverse problems/symptoms/ identities.