Final answer:
Natural selection is the primary force of adaptive evolution, promoting beneficial traits that enhance survival and reproduction, whereas other evolutionary processes can introduce harmful alleles. It shapes populations over time based on environmental pressures but cannot create new traits, only select among existing variations.
Step-by-step explanation:
Natural selection uniquely drives adaptive evolution by selecting for beneficial alleles that contribute to an organism's survival and reproductive success in its environment, while other evolutionary forces can introduce harmful alleles to a population's gene pool.
Evolution through natural selection is not about generating ideal organisms; it's about increased survival and reproduction of advantageous traits. Unlike genetic drift or gene flow, which can insert deleterious alleles, natural selection promotes advantageous alleles, thus increasing their frequency in the population. Often paralleled with artificial selection, natural processes determine which traits are favorable based on environmental pressures. This leads to populations that are better adapted to their surroundings over time, enhancing their overall fitness.
Natural selection can't create new traits but can shape existing genetic variations within the population by preferentially selecting traits that increase an organism's Darwinian fitness. It acts on whole organisms rather than on individual alleles, fundamentally guiding the path of adaptive evolution by amplifying beneficial characteristics and suppressing harmful ones.