Industrial Melanism in Peppered Moths

Industrial melanism is a phenomenon observed in the peppered moth (Biston betularia) where there is a higher prevalence of dark-colored (melanic) individuals in industrial areas compared to non-polluted areas. This phenomenon has been extensively studied and provides evidence for natural selection in action.

Explanation of the Correct Answer: Option D

The correct answer to the question is option D, which states that the true black melanic forms arise by a recurring random mutation. This answer is supported by the scientific understanding of industrial melanism in peppered moths.

1. Industrial Melanism and Natural Selection:
- Industrial melanism is an example of natural selection at work. In areas heavily polluted by industrialization, dark-colored moths have a higher survival rate compared to lighter-colored moths.
- This is because the dark coloration provides better camouflage against the soot-covered trees, making them less visible to predators such as birds.
- As a result, the frequency of the melanic form increases in industrial areas over time, while the lighter form becomes less common.

2. Recurring Random Mutation:
- The recurring random mutation refers to the genetic change responsible for the melanic form in peppered moths.
- The melanic form is caused by a mutation in a gene that controls the production of melanin, the pigment responsible for coloration.
- This mutation results in an increased production of melanin, leading to a darker coloration in the moths.
- The mutation is considered random because it can occur spontaneously in individuals and is not influenced by the presence or absence of pollution.

3. Selection Advantage:
- The melanic form of the moth has a selective advantage over the lighter form in industrial areas due to better camouflage.
- In non-polluted areas where trees are not covered in soot, the lighter form of the moth has a higher survival rate as it blends in better with the lighter-colored tree bark.
- Therefore, the melanic form is selectively favored in industrial areas, while the lighter form is favored in non-polluted areas.

4. Confirmation of the Recurring Random Mutation:
- The recurring nature of the melanic form in peppered moths has been confirmed through experiments and observations.
- Researchers have artificially selected for the melanic or lighter forms in laboratory populations and found that the melanic form can revert back to the lighter form through recombination or new mutations.
- This supports the idea that the melanic form arises from a recurring random mutation rather than being a pollution-generated feature.

In conclusion, the correct answer (option D) states that the true black melanic forms in peppered moths arise by a recurring random mutation. This explanation is supported by the observed industrial melanism phenomenon, where the melanic form has a selective advantage in polluted areas due to better camouflage.