I understand the impasse. I just don't think that "because it happened" is a very satisfactory answer. *BG*

survival means that either, 1. there was an organism of diverse genetic material, and survival dictated which direction the organism went from the options available within that diverse genetic material (a "subtractive" process), or 2. the organism had to achieve the change in anticipation of the need to survive an environmental change.

procreative success, of course, demands that the change (now without the impetus for change having been described) has already occurred so that future generations may inherit the change.

The "monster" is not, as you suggest, a large-scale change. It is merely a meaningful change. It doesn't necessarily demand multiple changes in genetic make-up. It only requires meaningful change in the genetic makeup.