A lot of the principals in actions haven't changed, but materials & processing have come along in a 100 years... I personally would not call polymer construction a micro-evolution. As the production costs of Nanoplastics come down we maybe able to see frames & grips that could easily conform to any shooter, by the shooter, with no risk of failure. 'A ceramic barrel enforced by carbon fiber on a totally plastic gun'. In 1899, there wouldn't have been even a thought on the subject. The gun industry is driven by demand, mostly by the military field. But it also seems to copy technologies proven in other fields and then implemented to their use. Not a new concept or original to the gun industry granted...
I think stagnation of development is driven by resistance of the end users bias towards nostalgia, not an industry's unwillingness to change designs... Glock's are a perfect example, people either love them or them. Not a judgment, just an observation. Same goes for a lot of safety features that have been tried to be incorporated into firearms that met with commercial failure.
Another perfect example of resistance, is the use of electronic ignitions. Still incorporated in some muzzle loaders, but I bet Remington is still pizzed about the reception their 700's received when introduced to the market....
