Odd patterns like stripes and jungles are thought to be caused by things that can fluctuate during incubation. Fluctuation of tempertures is NOT a proven way to make changes in patterns....I have never seen a ball python book state that as fact, only as a possible reason.

Reptile incubation has several different factors....but the two main factors are temperature and humidity. Modify those two things and might end up with all kinda genetic variations....you have the same chance of hatching a half formed ball python that dies 5 minutes after it hatches as you do of hatching a stripe or other oddity.