What does natural selection refer to in biological terms?

Natural selection refers to the concept where organisms that are better adapted to their environment tend to survive and reproduce more successfully than others. This means that the traits that enhance survival and reproductive success are more likely to be passed on to the next generation. The idea encapsulates the notion that, in a given environment, certain advantageous traits become more common over time due to this differential survival and reproduction.

While all the other options touch upon aspects of evolution or selection processes, the essence of natural selection specifically lies in the survival of the fittest—where "fittest" encompasses not just physical strength but the overall suite of traits that enhance an organism's ability to thrive in its specific environment. This iterative process leads to gradual changes in the population, resulting in evolutionary adaptations that reflect environmental pressures.