What's "severe enough" trauma to develop multiplicity?
Firstly, it is possible that multiplicity might not result from trauma. There might be other reasons, trauma might be one of many reasons. However, most research and anecdotal evidence, both inside of and outside of psychology, points to a very very strong relationship between trauma and multiplicity, and within the wide range of possibilities of traumas that can happen to someone, it seems likely that it most often happens with childhood, repetative trauma, the type that happens in abuse situations.
We'll tackle the abuse debate elsewhere. For now, let's start looking at trauma, and how strong it may need to be to cause either a personality to divide itself, choose two or more expressions of self, construct internal pseudo-psyches, or for a psyche to request external spiritual help...
Firstly, there is no solidly known or explained "severe enough". To give a good case in point here, from p. 265 Frank Putnam's Diagnosis & Treatment of Multiple Personality Disorder:
- Extreme inconsistency in parental behavior and contradictory expectations of the child by the parents have been repeatedly identified in the literature as characteristic of the childhood home situations of MPD patients.... The child may be praised and punished for the same behavior on different occasions.... The relationship between the parents is usually polarized and often places the child in double-bind situations. The child's elaboration of different alter personalities is thought, in part, to be an adaptive response to the inconsistent and radically different demands made upon him or her.
To elaborate this particular angle: this is in the section on Family Therapy and whether or not it's a good idea for multiples. It is not by any means saying that this is all that happens to make a multiple -- but nor is it saying that more than this is needed, so it's possible to extrapolate from this that it is possible that an individual who is subjected to this behavior will develop multiplicity to sort out the conflict between having to please someone impossible to please, and preservation of their sense of self-integrity/self-protection. One thing that's notable here is that this strongly parallels the section on multiples AS parents: these types of inconsistencies of behavior may happen in many parents who are multiple when dealing with their children. SO in other words, being multiple can possibly cause incidents that make it more likely that your children would become multiple....
From here, we can extrapolate that multiples might not all have been directly physically, sexually or even emotionally abused: all it might take is role-modeling coupled with the parenting style a multiple is perhaps likely to exhibit.
On the point of having no evidence that a particular multiple went through trauma, please see Crisses/TimeAndPlausibleDeniability -- essentially showing that IF there were severe enough trauma or abuse to "warrant" multiplicity, there's at least a darned good chance that a portion of the multiple's mental resources are dedicated to hiding it from the fronting portion of the system. That's part of the plausible deniability of it all: it's possible that if a multiple doesn't remember trauma or abuse at all, the protection mechanisms are working. A multiple not remembering trauma or abuse at all does not mean that it didn't happen.
In When Rabbit Howls, the person who sought psychiatric treatment (the woman) in The Troops is essentially vehemently claiming in the beginning that she was never physically penetrated -- with absolute clear conviction -- and it unfolds through the story that she's not only JUST been penetrated but she'd been repeatedly penetrated and not only by her human stepfather.
It's easy to run around saying something didn't happen, but after reading something like that, it's much easier to realize that there's just no way to know for sure...not until you have a VERY strong certainty that you've uncovered nearly everyone and are able to put your past back into a more linear perspective, with no remaining holes or blackouts.
Uncovering denial is almost harder than uncovering the trauma itself. Or maybe they go hand in hand.