The Setup:
* Moth Coloration: The peppered moth exists in two main forms: a light-colored form with dark speckles (the "typical" form) and a dark form (the "melanic" form).
* Industrial Revolution: During the 19th century, the Industrial Revolution in England led to increased air pollution, covering trees with soot. This darkened the bark of trees where the moths lived.
Natural Selection in Action:
1. Survival Advantage: Before the Industrial Revolution, the light-colored moths blended well with the lichen-covered tree bark, making them harder for predatory birds to spot. The dark moths were more visible and therefore more likely to be eaten.
2. Environmental Change: As the trees darkened with soot, the survival advantage shifted. Now, the dark moths were better camouflaged, while the light moths stood out against the soot-covered bark.
3. Differential Reproduction: Because the dark moths were better camouflaged, they were less likely to be eaten by birds. This meant they survived longer and reproduced more often, passing on their genes to the next generation.
4. Evolutionary Change: Over time, the proportion of dark moths in the population increased dramatically. This is because natural selection favored the dark moth phenotype, allowing it to survive and reproduce more successfully.
Key Points:
* Natural selection is not about "choosing" the best traits: It's about individuals with advantageous traits being more likely to survive and reproduce.
* The environment plays a crucial role: The change in the environment (soot pollution) drove the change in the moth population.
* Adaptation is not instant: The shift from light to dark moths took generations to occur as the more advantageous trait became more prevalent.
The peppered moth example demonstrates how natural selection can lead to evolutionary changes in a population, making it a powerful example of the process at work.
