In short
Natural selection is the process by which organisms with features better suited to their environment survive and reproduce more, so those features become more common over generations.
Charles Darwin described it. There must be variation between individuals, some of it inherited. More offspring are produced than can survive, so there is a struggle for resources. Individuals with helpful variations are more likely to survive and pass them on. Over many generations, the population changes. It is not the individual that changes in its life; the population changes.
Peppered moths in smoky towns were mostly dark, because dark moths on dark bark were less often eaten by birds. When the air became cleaner, pale moths became common again.
Also searched as: phet simulations natural selection.
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