Barbarian asks:
If you like, I can show you a simple dice game that will give you an increase in fitness or stasis depending on the environment.
Want to try it?
Both of us can play games with dice where we set the rules to get the results we want.
Only difference is, yours doesn't simulate reality. Mine starts with an unadapted population, and a specific environment. What happens is that random mutations in the genomes of the individual organisms change their fitness. (you've already said that this is observable)
Then, the system evaluates the fitness of each organism, and only the most fit get to reproduce.
What follows is a period of rapid change in the population, which gradually slows to stasis.
Precisely what you claimed could not happen under such circumstances.
Interestingly, if there is more than one niche open, the population tends to diverge into two populations, each fit for a specific environment.
Again, precisely what we see in nature, but what creationism claims is impossible.
Want to try it?