Final answer:
Natural selection most accurately describes the nonrandom survival and reproduction of individuals with heritable traits that confer advantages in a given environment, leading to adaptive evolution. It is not a random process, nor does it create genetic variation, but instead acts on existing variation.
Step-by-step explanation:
Which of the following most accurately describes natural selection? The answer is A. The nonrandom survival of hereditary variants through many generations. Natural selection is a fundamental mechanism of evolution, favoring individuals that have heritable traits which provide an advantage in their environment. This process does not create new genetic variation but selects for traits that enhance survival and reproductive success among the variants that do exist.
Natural selection acts on the phenotype of an organism, which is the set of observable characteristics or traits. It leads to increases in allele frequencies for those traits that are advantageous in a given environment and decreases for those that are not. Over time, this can result in populations that are better adapted to their environments, though it does not strive to create 'perfect' organisms or operate with any predetermined goal.
While mutation is a random process generating genetic diversity, natural selection is the nonrandom differential survival and reproduction of individuals. The combination of these processes allows for adaptive evolution, where advantageous traits become more common in a population over generations.