> Actually, the ability to respond to never-seen-before threats is the whole purpose of the adaptive immune system [1].
But the poster I was responding to was claiming that our immune system should have evolved the ability to not respond to those threats, but anticipate their specific forms without seeing them. That vaccination as a concept is hogwash because if it was useful, we'd have done it through evolution. But that's plainly nonsensical - we wouldn't need a system that functioned by random variation if we evolved the ability to know what the real targets would be, but we couldn't do that without specific knowledge, which we can't get without being exposed to the things, by which time ... it's too late to have then already built the specific defenses.
But the poster I was responding to was claiming that our immune system should have evolved the ability to not respond to those threats, but anticipate their specific forms without seeing them. That vaccination as a concept is hogwash because if it was useful, we'd have done it through evolution. But that's plainly nonsensical - we wouldn't need a system that functioned by random variation if we evolved the ability to know what the real targets would be, but we couldn't do that without specific knowledge, which we can't get without being exposed to the things, by which time ... it's too late to have then already built the specific defenses.