Question

what is the main reason why genetic variation is necessary for a population?
it allows a population to react to environmental changes.
it makes all individuals in a population identical.
it guarantees that the environment will remain stable.
it prevents any changes from occurring in a population.

Explanation:

To determine the main reason genetic variation is necessary, we analyze each option:

• The first option (top) states it "allows a population to adapt to environmental changes" – this aligns with evolutionary theory, as genetic variation provides the raw material for natural selection, enabling populations to evolve in response to environmental pressures.
• The second option ("makes all individuals... identical") is incorrect, as genetic variation promotes diversity, not uniformity.
• The third option ("guarantees the environment... stable") is false, as environments are dynamic, and genetic variation helps populations adapt to change, not stabilize the environment.
• The fourth option ("prevents any changes...") is incorrect, as evolution and population change are driven by genetic variation (along with other factors), so variation does not prevent change.

Thus, the correct reason is that genetic variation enables adaptation to environmental changes.

Answer:

The top option (text: "It allows a population to adapt to environmental changes")