Questions: Which statement describes natural selection? It is the primary mechanism for evolution. It must act on structural traits. It acts to cause overpopulation. It causes learned skills to become heritable traits.

The answer is the first one: It is the primary mechanism for evolution.

Explanation for each option:

1. It is the primary mechanism for evolution.

   • This statement is correct. Natural selection is a key process in evolution, where organisms better adapted to their environment tend to survive and produce more offspring. Over time, this leads to changes in the traits of living organisms, driving evolutionary change.

2. It must act on structural traits.

   • This statement is incorrect. Natural selection can act on any heritable trait that affects an organism's fitness, not just structural traits. This includes behavioral, physiological, and biochemical traits.

3. It acts to cause overpopulation.

   • This statement is incorrect. Natural selection does not cause overpopulation. Instead, it often acts in response to environmental pressures, which can include factors like resource scarcity that limit population growth.

4. It causes learned skills to become heritable traits.

   • This statement is incorrect. Learned skills are not heritable traits. Natural selection acts on genetic variations that are passed from one generation to the next, not on skills acquired during an organism's lifetime.

In summary, natural selection is the primary mechanism for evolution, acting on heritable traits that affect an organism's ability to survive and reproduce.