The peppered moth (Biston betularia) provides a textbook example of natural selection in action.
The Setup:
* Variability: Peppered moths exist in two main forms: light-colored (peppered) and dark-colored (melanic). This color difference is due to genetic variation within the species.
* Environment: Pre-industrial England, the trees were covered in light-colored lichens, providing camouflage for the light-colored moths. Dark moths stood out against the light background, making them easy prey for birds.
The Change:
* Environmental Pressure: The Industrial Revolution introduced significant air pollution. The soot from factories killed the lichens and darkened the tree trunks.
* Selective Advantage: The dark-colored moths were now better camouflaged against the dark tree bark. They were less likely to be eaten by birds and had a higher chance of survival and reproduction.
* Shift in Population: Over generations, the frequency of dark-colored moths increased dramatically. This happened because the dark moths, better adapted to the polluted environment, produced more offspring, passing on their genes.
The Result:
Natural selection, driven by the environmental change of industrial pollution, favored the dark-colored moths. This led to a shift in the moth population from predominantly light-colored to predominantly dark-colored.
Key takeaways from this example:
* Variation: Natural selection requires existing variation within a population.
* Selective Pressure: Environmental factors like pollution or predator pressure can act as selective pressures.
* Adaptation: Individuals with traits better suited to the environment are more likely to survive and reproduce.
* Evolution: Over time, the population evolves as the frequency of advantageous traits increases.
The peppered moth example demonstrates how natural selection can lead to rapid evolutionary change in response to environmental pressures. It is a powerful illustration of how the environment shapes the evolution of life.
