Given that a hammer is a primordial tool, a first tool, you'd think that that switch would be the most striking at that moment. We went from having no tool at all to a tool.

I think you're mixing definitions of things. We don't lose any capacity at all, we just lose the need for a skill in our day to day life. We haven't evolved away from the ability to create fire, we just don't need that knowledge at this moment. I don't know how to hunt a gazelle, but the hunter didn't know how to drive.

Both "evolution" and "capacity" seem to be incorrect words to describe this phenomena.