That has been done, several times. Here is brief outline of one done in Brazil: There were tiny fish that sexually matured very quickly (in much less than one year) living with larger fish that ate them below a water fall but not above it. Evolution theory suggested the reason they were smaller earlier egg layers of only a few eggs was the selection pressure of the bigger fish. (Little fish that had genes delaying sexual maturity could lay more eggs later but were eaten before those genes could be reproduced.) So to test evolution in less than ten years (Some Ph.D. candidates did not want to be "professional students" as I did with ~10 years at JHU) they netted a couple of hundred tiny fish and moved them above the water fall where there were none of the bigger fish. About 20 to 30 generations later, JUST AS EVOLUTION PREDICTED, the tiny fish were several times larger when they became sexually active and lived for four or five years, laying hundreds of times more eggs than when selection favored the "lay eggs early" genes. Now, above the water fall, the genes that made early sexual maturity with only a few eggs laid were selected against. I.e. the chance of 10 or 20 of those eggs with "early mature and lay eggs genes" winning the survival struggle with limited food against >10,000 eggs from the fish with "delay maturity, lay more eggs, live longer" genes was so little that AS EVOLUTION PREDICTED, the "mature quick, lay a few eggs" genes became extinct in the gene pool above the water fall but not below where selection pressure of the bigger fish favored the "mature quick, lay a few eggs" genes. Nice thing about this experiment (in addition to the Ph.D.s it produced) was that there is no alternative way to explain the observed results as both the tiny fish below and their evolved "cousins" above the falls lived in exactly the same water. If there were any difference (say some fish eating birds operating on both groups, that would work against the evolution predicted and observed results as like the bigger fish below the falls, that is some slight selection pressure helping the "mature quick, lay a few eggs" gene fishes. (lay eggs before some bird eats you.) I will note however, that despite your stating this "would prove you wrong" I am confident you will not admit that. - Facts are totally ineffective against those "possessed by the faith."