How Natural Selection Works
Explain natural selection as the mechanism of evolution: heritable variation + competition for resources + differential survival and reproduction = change in allele frequency over generations
What a learner can do afterwards
- Describes the four conditions required for natural selection to operate (variation, heritability, competition, selection)
- Applies the concept to a specific example (e.g. antibiotic resistance in bacteria, peppered moth)
- Explains why individuals with advantageous traits leave more offspring
- Distinguishes natural selection from evolution (selection is the mechanism; evolution is the result over many generations)
The lesson
You already know that individuals vary, and that new variation starts with mutations in DNA. Natural selection is the process that decides which of those variations become more common over time. It needs four things to work: variation between individuals, traits that are heritable so they pass from parent to offspring, competition for limited resources like food or mates, and differences in how well individuals survive and reproduce because of those traits.
A hospital treats an infection with an antibiotic. Most bacteria die, but a few already carried a mutation that let them survive the drug, purely by chance. Those survivors are not choosing to become resistant; they just happen to have a trait that helps them live. They reproduce, and their offspring inherit the resistance gene. After many generations of this, most bacteria in the population carry it.
Natural selection is not the same as evolution. Selection is what happens within one generation: some individuals survive and reproduce more than others because of a trait they already have. Evolution is what you see after selection repeats over many generations, when the population's mix of traits has clearly shifted. And no organism is choosing anything. The resistance gene existed in a few bacteria by chance, long before the antibiotic ever showed up.
Variation, heredity, competition, and unequal survival make up natural selection; repeated across generations, that adds up to evolution.
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.