What drives the process of natural selection within a population?

The process of natural selection is primarily driven by selection pressure, which refers to external factors that influence the survival and reproductive success of individuals within a population. These pressures can take various forms, such as environmental conditions, predation, competition for resources, and disease.

When certain traits give individuals a better chance of surviving and reproducing under these pressures, those traits become more common in the population over generations. This leads to adaptive evolution, where the population becomes better suited to its environment.

Unlike genetic drift or gene flow, which affect allele frequencies in a population through random changes or the movement of individuals, respectively, selection pressure directly relates to how specific traits impact an organism's ability to thrive in its environment. Population bottlenecks refer to significant reductions in population size which can lead to a loss of genetic diversity but do not directly drive the selective advantage of traits. Thus, the correct answer highlights the core mechanism behind natural selection and the adaptive evolution it fosters.