Question

which of the following statements best reflects how evolution occurs? populations evolve as their inherited traits change across generations. evolution always leads to increased complexity. individual organisms evolve traits during their lifetimes. evolution occurs only when new species form.

Explanation:

• For the option "Populations evolve as their inherited traits change across generations": Evolution is a change in the heritable characteristics of biological populations over successive generations. Populations, not individuals, are the unit of evolution because traits are passed down through generations and allele frequencies in a population change over time.
• For "Evolution always leads to increased complexity": This is incorrect. Evolution can lead to simpler forms (e.g., loss of eyes in cave - dwelling organisms) as long as the trait is adaptive.
• For "Individual organisms evolve traits during their lifetimes": Individuals do not evolve during their lifetime. An individual's traits are relatively fixed during its life, and evolution acts on populations over generations through processes like natural selection, genetic drift, etc.
• For "Evolution occurs only when new species form": Evolution can occur within a species (microevolution) through changes in allele frequencies, not just when a new species is formed (macroevolution).

Answer:

Populations evolve as their inherited traits change across generations.