Which principle describes the mechanism of natural selection?

The principle that describes the mechanism of natural selection is encapsulated in the phrase "Survival of the Fittest." This concept, popularized by Charles Darwin, emphasizes that within a population, individuals with traits that provide a competitive advantage in a given environment are more likely to survive, reproduce, and pass these favorable traits to the next generation.

Natural selection operates on the variation present in a population. Those individuals whose characteristics better suit them to their environment are favored and thus have higher reproductive success. Over time, this process leads to adaptations in the population, enhancing their overall fitness in their environment.

The other principles listed—adaptive radiation, genetic drift, and endemic species—describe different biological concepts. Adaptive radiation refers to the diversification of species to fill various ecological niches, genetic drift involves random changes in allele frequencies in a small population, and endemic species are organisms that are native to a particular area and not found elsewhere. While all these concepts are important in the study of evolution, they do not specifically define the mechanism of natural selection as effectively as "Survival of the Fittest."