The silly thing is that they feel a need to justify it. They're speaking English, every single word they say carries an incredible history of the world we live in from Rome to the speakers of Old Norse and otherwise. The simplest solution is a handwave: the creators translated everything out of Galactic Basic for you.
I mean, go for it? I'm sure the army would welcome the opportunity to invest in effective armor research, so if you can get it off the ground at all contact DARPA.
No matter how many times you let that happen to a bacteria, as long as you're killing them with a handgun, it keeps working. They don't evolve defenses without becoming something different.
So I guess it's a bit metaphorgotten, but the point is that that's only true if it's a system where starting from zero to a billion is something that can be selected for, and it pretty much just is not.
