How can natural selection contribute to antibiotic resistance?

• A. Antibiotics instantly kill all bacteria making resistance unnecessary.
• B. There is no effect of natural selection on bacteria.
• C. Bacteria with resistance traits survive and reproduce, spreading resistance genes.
• D. Resistance arises only through non-heritable changes.

Answer: (C)

Natural selection acts by increasing the frequency of traits that help an organism survive in a given environment. When antibiotics are present, most bacteria that are susceptible die, but some carry resistance traits—mutations or resistance genes on plasmids—that let them withstand the drug. These survivors reproduce, passing the resistance to their offspring, and sometimes even transferring resistance to other bacteria. Over time, the population becomes dominated by resistant individuals, making the antibiotic less effective. This explains why resistance spreads: the drug environment favors those few with resistance traits, and those traits are (at least in part) heritable.