[Sabertooth]

I believe that are certain well defined portions or domains of DNA utilized in the creation of elements of the immune system which do mutate at significantly increased rates, and that this is part of a mechanism allowing the system to more rapidly create antibodies that bind strongly to foreign cells or particles.

Ah, very interesting... I hadn't considered an anti-body model for latent mutagenic capacities.

I'm flagging a couple of the FR doctors and scientists to see if they can shed any light on what you're describing.

[Stultis]

Real quick, here is a short historical primer on the immune system and antibody production.

[Rudder]

For clarification:

Spontaneous implies no casuation; The two examples that may be useful, e.g., bacterium and immune cells may well be responding to extraneous stimuli, either radiation or foreign material. Their mutigenesis in these circumstances may not be "spontaneous."

Random may not be applicable either. Responding to an environmental stressor may well be a non-random event.

That said, this does not reduce the signifcance of mutagenesis that has the appearance to be both random and spontaneous.