I have a lot of information to back up my statements, probably more than you want to hear or digest in one setting
I'll list some examples of evolutionary changes without "man's" interference, that would disprove the commonly believe concept of osmoregulation/homeostasis!
Oreochromis mossambicus, can live in pure freshwater, and salt water up to 1.035, greater specific gravity than the red sea, where most fish will die. They can breed in both conditions, and I've seen so myself personally! <---that is concrete evidence.
Guapote from Costa Rica, and other central american countries, have been found in Coastal waters, and full marine waters. There was a TFH article on it, you Cichlidae people should read it.
Alligator gars, are found in the Gulf Coast.
I can name and think of hundreds more that are this way.
Are you saying that these fish have mechnical parts in them that switch from drinking water to excreting urea to keep homeostasis? Or they've adapted?
Why, do black people in Africa who are exposed to the sun have darker skin and white people from Europe who see more fog and clouds have lighter skin, even their immediate off springs are born like that? Are these all just random happenings?
Science itself is constantly changing. Evolution does take place, in the aquarium, in the wild, etc. First comes hypothesis, then from repeated testings, supported by data, forms theories, and over time proven, becomes "facts" which are still not concrete. Our minds are very finite, and the ability to comprehend is limited, some more than others.