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What is natural selection?

Natural selection is the process by which organisms with advantageous inherited characteristics are more likely to survive, reproduce and pass those alleles on.

Natural selection explained

It requires variation within a population, a selection pressure, differential survival, and inheritance of the advantageous alleles across generations.
Over long periods the allele frequency in the population changes, and this accumulation of change is evolution. Antibiotic resistance is the fastest-observed modern example.

Key formula

variation → selection pressure → differential reproduction → allele frequency change

Worked example

Bacteria with a resistance allele survive antibiotic treatment and reproduce, so the resistant strain spreads.

Examiner tip

Never say organisms 'want' or 'try' to adapt. Variation already exists by chance, and selection acts on it.

Natural selection: common questions

What causes variation in a population?
Mutation, and in sexually reproducing species the reshuffling of alleles through meiosis and fertilisation.
How does antibiotic resistance develop?
A random mutation gives some bacteria resistance; antibiotics kill the rest, leaving the resistant bacteria to reproduce.

Related terms

DNA

DNA is the double-helix molecule that stores genetic information as a sequence of four bases along a sugar-phosphate backbone.

Mitosis

Mitosis is nuclear division that produces two genetically identical daughter cells, used for growth, repair and asexual reproduction.

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