You are, perhaps, talking about the chaotic influences on outcomes. The butterfly effect. The inability to perceive the eventual outcome due to the massive potential for variation, through those subtle influences. How, indeed, to sum all that up in a word? There must be a word for it, as it could apply to the evolution of a species, to climate change or even to an ant climbing to the very top branch of a mature oak tree.
...How about 'capricious'?
Meaning: 1. subject to, led by, or indicative of a sudden, odd notion or unpredictable change; erratic: "He's such a capricious boss I never know how he'll react".
...But here it is used subtly, not as a sudden jolt, but methodically random nuances, slowly over time:
Quoting Walter Bagehot: "Our law very often reminds one of those outskirts of cities where you cannot for a long time tell how the streets come to wind about in so capricious and serpent-like a manner. At last it strikes you that they grew up, house by house, on the devious tracks of the old green lanes; and if you follow on to the existing fields, you may often find the change half complete."
But also perhaps...'elusive', as in difficult to nail down where things are going to be.
Then again, maybe not. :-/ nice question. I look forward to seeing what comes back!