You're refering to Punctuated Equalibrium, Sasha - and like many people you have it slightly wrong.
PE (if it even occurs, and there is significant doubt) is pretty rapid compared to 'vanilla' evolution. PE can occur over hundreds of thousands of years, instead of millions.
I'm not familiar with the minnow experiment you describe, but it's not terribly relevant to the discussion at hand due to the tiny population of the fish tank. Whilst the colouration was no-doubt a survival trait the fact is that in a small enough population qany aberation, beneficial or otherwise has both a much higher chance of appearing (small populations encourage double-recessive traits to manifest) and flourishing (due to lack of genetic competition). Case in point, there is a village in Africa with no collar bones (cleidocranial dysostosis) - hardly a survival trait, but that's small populations for you. A sailor with the condition visited them in the 19th century, knocked boots with a local woman (or ten) and the whole village has it now.
Long story short, 38'000 years ain't long enough by an order of magnitude.
Looking for a friendly wargaming club on the Isle of Wight? Drop me a line.
Sisters of Battle - The Order of Glory Undimmed - 2'500 Points | High Elves - House Cyredeth - 2'500 Points | Bretonnians - The Muster of Sir Jules Estelle - 3'000 Points