This makes the assumption that evolution results in a perfect organism, which it does not. Instead, it results in a "good enough" organism.
The definition of "good enough" for bacteria has changed over the last 50 years, so these changes are occurring now. It doesn't necessarily require a cost, or at least not a cost that matters to humans.
The definition of "good enough" for bacteria has changed over the last 50 years, so these changes are occurring now. It doesn't necessarily require a cost, or at least not a cost that matters to humans.