In a sooty industrial city, dark moths hid better on grimy trees while pale ones got eaten, so each generation grew darker. No moth chose to change — natural selection simply let the best-camouflaged survive to have young.
Descent with modification
Natural selection, described by Charles Darwin, needs three things: variation among individuals, heritability of that variation, and differential survival or reproduction. Individuals with traits better suited to the environment tend to leave more offspring, so those traits become more common over generations. Populations evolve — individuals do not.
A single moth doesn't change its color to survive. Rather, better-camouflaged moths survive and reproduce more, shifting the population's makeup over time.
During industrial pollution in England, dark peppered moths were better hidden on soot-darkened trees and became more common — a documented case of selection.
- A beetle population varies in shell hardness, an inherited trait.
- A new predator cracks soft shells more easily.
- Predict how the population changes over generations.
What you should see: Hard-shelled beetles survive and reproduce more, so average shell hardness rises over generations — natural selection in action.