Life Sciences 11 · Biology · Lesson 9.2
Natural selection
- Level
- Grade 11
- Reading time
- 13 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Variation, fitness and how populations change over time.
What is natural selection?
Short answer
Natural selection is the process by which heritable traits that improve survival and reproduction become more common in a population over generations. Individuals vary; some variations give a reproductive advantage in a given environment, so those individuals leave more offspring. Over time this shifts the population’s traits — the core mechanism of evolution described by Darwin.
Concept preview
What you will be able to do
- 01State the observations behind natural selection and explain how they combine to change populations.
- 02Define fitness and adaptation and use the terms correctly.
- 03Compare directional, stabilising and disruptive selection, and relate natural to artificial selection.
- 04Identify and correct common misconceptions about how natural selection works.
In 1858 two naturalists, Charles Darwin and Alfred Russel Wallace, independently arrived at the same revolutionary idea, and a year later Darwin published it in full in On the Origin of Species. That idea was natural selection — a natural, unguided mechanism that can, over many generations, reshape living things and even produce entirely new species. Its brilliance is that it needs no designer and no goal; it follows automatically from a few simple facts about how organisms live and reproduce. The fact that two people reached the same conclusion from different observations gave the idea immediate weight. Understanding those simple facts, and how they combine, is the key to understanding all of modern biology, because natural selection is the main engine that drives evolution.
School Plan
Natural selection
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Related topics
Frequently asked questions
- What are the requirements for natural selection?
- Variation in traits, heritability of those traits, and differential survival or reproduction based on them.
- Is natural selection the same as evolution?
- No. Natural selection is one mechanism that causes evolution — the change in a population’s allele frequencies over time.