The primary mechanism of evolution described by Darwin is natural selection. Darwin proposed that, within a population, individuals exhibit variation in traits, some of which confer a survival advantage. These advantageous traits are more likely to be passed on to subsequent generations through reproduction. Over time, natural selection can lead to populations adapting to their environments, giving rise to new species. This process illustrates how genetic variations create differences in fitness and survival, ultimately shaping the biodiversity of life on Earth.