Natural selection is the mechanism by which heritable variation leads to differential survival and reproduction in changing environments in evolving populations.
Coverage 2013–2023 · Updated 16 Jul 2026
Natural selection is differential survival and reproduction caused by heritable differences; over generations it changes populations and drives evolution.
Heritable variation exists → an environmental or biological pressure affects individuals differently → some genotypes leave more surviving offspring → their alleles become more frequent → population characteristics change.
Operating continuously over billions of years, repeated selection has contributed to life's biodiversity. It can also be observed over short timescales when pressures are strong.
Darwin supplied a convincing selection mechanism and displaced Lamarckian explanations based on inherited acquired characteristics. Replacing a dominant explanatory framework in this way is a scientific paradigm shift.
Individuals do not evolve because they need to. Selection acts on existing phenotypic differences, while evolutionary change is measured across generations.
This objective is assessed through essay response, commonly using Explain / Identify / Evaluate.
Explain / Identify / Evaluate / Outline / State / Describe / Discuss
Build the answer around this relationship: Natural selection acts on individuals but changes populations across generations.
Representative question
Explain how evolution may happen in response to environmental change with evidence from examples.
Core D4.1 examples follow the same causal route: heritable variation exists, a selection pressure acts, individuals differ in fitness, and alleles linked to higher reproduction become more common. Endler’s guppies and sexual selection are evidence versions of the same chain.
Core natural-selection exam answers should never stop at “the best adapted survive.” They need the chain: heritable variation exists, a named pressure acts, some individuals have higher fitness, and their alleles become more common over generations. Use this for abiotic pressure, overproduction, sexual selection, and Endler-style data.
