Organisms better adapted to their environment tend to survive and produce more offspring.

• A. Gene flow
• B. Natural selection
• C. Genetic drift
• D. Evolution by mutation

Answer: (B)

This describes natural selection, the process by which heritable traits that help an organism survive and reproduce become more common in a population. When the environment favors certain characteristics, individuals with those traits tend to live longer, find mates, and leave more offspring. Their advantageous genes therefore become more frequent in the next generation, and the population becomes better adapted over time.

Other mechanisms can influence evolution, but they work differently. Gene flow involves the movement of genes between populations, changing allele frequencies across groups rather than through differential survival in a single population. Genetic drift is random change in allele frequencies due to chance events, not driven by how well traits help organisms survive. Mutations introduce new genetic variation, but whether that variation sticks around depends on selection acting on those traits.