Biology – Natural and artificial selection | e-Consult

Antibiotic resistance in bacteria is a classic example of natural selection in action. Bacteria populations naturally exhibit genetic variation, including variations in genes that code for cell wall structure or mechanisms to expel antibiotics. When an antibiotic is introduced, it acts as a strong selection pressure, eliminating most of the susceptible bacteria.

However, bacteria with pre-existing resistance – due to random mutations or acquisition of resistance genes from other bacteria – are more likely to survive the antibiotic treatment. These resistant bacteria then reproduce, passing on their resistance alleles to their offspring.

Over time, the proportion of resistant bacteria in the population increases dramatically. This is because the antibiotic is effectively eliminating the susceptible bacteria, leaving only the resistant ones to thrive and multiply. The resistance becomes increasingly prevalent within the population, leading to the evolution of antibiotic-resistant strains. The process demonstrates how variation, selection pressure (the antibiotic), and inheritance (passing on resistance genes) work together to drive evolutionary change.