Despite huge populations and superfast reproductive times, however, they never become anything more than humble bacteria. Moreover, such mutations exact a fitness cost. The resistant strain of bacteria has an advantage against an antibiotic, but not because it has evolved a superpower. Rather, it has lost something that just happens to give it an advantage in that odd environment. When the antibiotic-resistant bacteria must compete with the ordinary strain of bacteria absent the antibiotic drug, the ordinary strain wins.
