Modern Synthetic Theory of Evolution > Natural Selection

Estimated time: 6 minutes

CISCE: Class 12

Key Points: Examples of Natural Selection

Example of Natural Selection	Selective Pressure	Outcome	Significance
Industrial melanism (Peppered moth)	Pollution darkened tree trunks	Dark (melanic) moths survived better than light moths	Demonstrates environmental selection acting on colour variation
DDT resistance in mosquitoes	Use of DDT insecticide	Only resistant mosquitoes survived and reproduced	Shows selection of resistant genotypes
Sickle-cell anaemia	Malaria infection	Heterozygotes survive better in malaria-prone areas	Example of balanced polymorphism
Antibiotic resistance in microbes	Use of antibiotics	Resistant microbes survive and multiply	Illustrates rapid natural selection in microorganisms

Maharashtra State Board: Class 12

Natural selection is the process where better adapted individuals survive and reproduce more, leading to evolution (“survival of the fittest”).
It acts on genetic variations in a population and causes changes in gene frequency over generations.
According to Darwin, natural selection is the main driving force of evolution and leads to the formation of new species over time.
Example: Industrial melanism in Biston betularia, where black moths increased in polluted areas due to better camouflage, while white moths decreased.
Types of natural selection include stabilising (favours the average), directional (favours one extreme), and disruptive (favours both extremes).
Natural selection removes harmful traits and favours useful adaptations, helping organisms survive in changing environments.