Species Overview
The Peppered Moth (scientific name: Biston betularia) is a classic example used in evolutionary biology to explain natural selection.
It is native to Europe and North America and is known for two major colour forms:
- Light (typica) form – pale with black speckles
- Dark (melanic) form – almost completely black
What are Darker Peppered Moths?
Darker peppered moths are the melanistic variant of Biston betularia.
They have a higher concentration of melanin pigment, making their wings appear dark or black. This condition is known as industrial melanism.
Industrial Revolution and Natural Selection
During the Industrial Revolution (19th century Britain):
- Factories released soot and pollutants.
- Tree trunks became dark due to industrial smoke.
- Lichens (which made trees lighter in colour) were destroyed.
Before Industrial Pollution
- Light moths blended well with lichen-covered trees.
- Dark moths were easily visible to predators (especially birds).
After Industrial Pollution
- Tree bark became dark.
- Light moths became visible and were preyed upon.
- Dark moths were better camouflaged and survived more.
As a result, the population of darker moths increased significantly.
Evolutionary Significance
The case of darker peppered moths is considered:
- A textbook example of Darwin’s theory of natural selection
- Evidence of adaptation due to environmental change
- An example of directional selection
When pollution levels declined in the 20th century due to environmental regulations, the frequency of light-coloured moths increased again.
This shows that natural selection is dynamic and environment-dependent.
Key Concept: Natural Selection
Natural selection works through:
- Variation within a species
- Environmental pressure
- Differential survival
- Reproduction of advantageous traits
In this case, dark coloration became advantageous in polluted environments.
