But how then, if a mutation is beneficial in one environment, but deleterious in another, do we define exactly what an advantageous mutation is?
That which survives in an environment is beneficial by definition. That which perishes in an environment is deleterious by definition.
When you go shopping you pick the best fruits and vegetables available to purchase.
It is all relative to what else is around to compete.
I might be able to kick snot on an elementary school kid(deleterious) but be placed in my casket by Mike Tyson(beneficial).
Again as I understand it.