Which statement best describes natural selection?

• A. The genetic drift of populations over time.
• B. Differential survival and reproduction due to heritable variation, leading to adaptation over generations.
• C. A sudden mutation causing new traits in a single individual.
• D. A gradual loss of genetic variation due to bottlenecks.

Answer: (B)

Natural selection is the differential survival and reproduction of individuals due to heritable variation, leading to adaptation over generations. In a given environment, individuals with advantageous traits leave more offspring, so those traits become more common in the population over time. This relies on existing variation and heredity, with new variation arising by mutation and then being sorted by fitness across generations.

The other ideas describe different evolutionary processes: genetic drift refers to random changes in allele frequencies that occur by chance rather than because of fitness differences; a sudden mutation in a single individual is just a mutation event, not the selective sorting that drives adaptation; and a bottleneck reduces genetic variation through a drastic population decline, which can affect evolution but is not the mechanism by which natural selection operates.