What is the primary mechanism behind natural selection?

The primary mechanism behind natural selection is the concept often summarized as "survival of the fittest." This phrase refers to the idea that individuals with traits better suited to their environments are more likely to survive, reproduce, and pass those advantageous traits to the next generation. This process results in the gradual evolution of species, as advantageous traits become more numerous in the population over time.

Natural selection operates through the differential survival and reproduction of organisms based on their genetic variations. Those variations arise primarily from random mutations, but natural selection is the process that determines which mutations will contribute to future generations. The "fit" in "survival of the fittest" pertains not necessarily to strength or size, but rather to how well-suited an organism is to its specific environment and ecological niche.

While concepts like random mutation and environmental adaptation do play significant roles in the larger context of evolutionary biology, they are not the driving mechanism behind natural selection itself. Artificial breeding, by contrast, involves human intervention and is not a natural process, thus falling outside the scope of natural selection as well.