A situation in which a mutation (darker wings) helped moths to survive in a changing environment (darker tree bark). The moths that had the darker wings were more likely to live longer enough to reproduce, and thus more moths inherited dark wings. Later, the process reversed itself. Explain why the reverse occurred and how this second change relates to the process of evolution.
The reverse occurred because of changes in the environment. As pollution levels decreased and tree bark became lighter, lighter-winged moths became more difficult to spot and were thus more likely to survive and reproduce. This led to a decrease in the population of dark-winged moths and an increase in the population of light-winged moths.
This second change relates to the process of evolution because it shows how the traits within a species can change over time in response to changes in the environment. The moths with darker wings were better adapted to the environment with darker tree bark, and thus had a higher survival and reproductive rate. However, when the environment changed, the traits that were once beneficial became less advantageous, leading to a shift in the population towards those with lighter wings. This process of natural selection ultimately results in changes in the genetic makeup and physical characteristics of a species over time, as the traits that are best suited to the environment are passed on to future generations.