Question

Prior to the industrial revolution in the mid-1800s, a species of moth had light-colored wings speckled with small black spots. This coloration camouflaged the moths resting on the birch trees growing in their native habitat, since birch bark has similar coloring. In the early 1900s, this changed as dark soot produced by industrial pollution coated birch trees such that the trees lost their speckled coloring. Years later, it was observed that the moths of this species had changed from being light and speckled to being solid black. Which is the most plausible reason for this change

Answer 1

The dark colored moths were due to a genetic mutation, and were more than likely present before the Industrial Revolution. Their fitness was low because predators could easily see them on the light-colored trees. They would be eaten before they could reproduce and pass on their genetic mutation. After the trees became darkened by soot, the darker colored moths now had the survival advantage, able to "hide" from predators. The lighter colored moths became more visible to predators, and the advantage shifted. Now, the light colored moths were more visible to predators, were eaten, and didn't have the chance to reproduce. The darker moths with the mutation had the survival advantage, blending in with the soot-covered trees, and were able to reproduce at higher rates, passing the mutation on to later generations.