Probably the biggest evolution is skills have become more ubiquitous. What were amazing stuff that were the tools of a few select fighters are adopted far more across the board. Then, the big thing most people miss is the adaptations to take those skills away from fighters in a fight.
The old cliche is; everybody looks like a champ hitting the heavy bag. Which is to say, what great fighters do is limit the tools thier opposition can use in a fight, choke them of options and force them into areas of the fight that favour the great fighter or set traps in the same manner, exploit what the other guy thinks they are good at. The better a fighter the harder (in general) it is to take stuff away from them they lean on as core to thier style . As a sidenote, this is one of the main reasons a good jab (aside from set ups) or being able to hurt someone to make them respect you are so important. Two of the most important tools to take stuff away from the other guy. If you can't make a guy respect you he can throw with far more impunity. If you can't check someone at range they have so many more options.
The cycle is
Innovation, adoptation by the masses, adaptation, negation and exploitation of what was innovative and so on. As a combat sport matures the innovations become smaller and more tailored. Sometimes more discrete (a specific defence for a sub for example) or more generalized (changes to stances). Then, like fashion, a technique might fall out of usage for sometimes decades (I'm talking about boxing or MT precedents here) until it becomes unusual and innovative again. Or a new innovation may necessitate an old technique as a counter tactic.
I could list all sorts of specifics but this is the general pattern trainers and fighters (once again I'm far more familiar with MT and boxing for the purposes of training) work through.
Evolution never stops, it just becomes harder to discern from the outside unless it's something overt like calf kick adoption (which is a recycled technique in and of itself).
