This would seem to be one example of what Izzy was looking for. The only exception is that there isn’t a constant selection pressure, and there will be no clear winner unless drought becomes the norm, or becomes totally unheard of. It would be nice if there were a good example where a species has a trait that is a very obvious advantage. The problem with this though, is that if something offers an unequivocal advantage, it is likely to outcompete others in the population in a very small number of generations. This means we have a small chance of actually observing it.
I just remembered yet another bit of biochemical evidence for evolution:
There is a type of mutation called a “frameshift mutation” which comes from the fact that DNA bases are read three at a time. Thus a sequence like:
AAA GGG TTT AAA CCC
can be frameshifted into
AAG GGT TTA AAC CC…
if you remove the first A, and the new sequence will have the same DNA sequence, but the resulting protein will be completely different.
There are proteins which have completely different sequences , structures, and functions, but almost the same DNA sequence, because they are related by a frameshift. In one case I saw recently, the deleted DNA base was in the middle of the protein, so that the first half was the same but the second half was frameshifted. There was also a case of a bacterium which, within the last few years, got a frameshift mutation which created a protein that enabled the bacterium to digest vinyl. That tiny ability of the newly scrambled protein was enough for natural selection to take hold, and it evolved to digest vinyl quite well.
-Ben