Heritable variation can change through differences in reproductive contribution.
Key knowledge
Natural selection occurs when heritable differences affect organisms' contributions to later generations. Variants associated with greater reproductive contribution in the relevant environment can become more frequent, producing adaptation under suitable conditions.
Conditions and scope
Requires heritable variation and differences in reproductive contribution; survival alone is not the definition of fitness.
The outcome depends on environment, tradeoffs and available variation, and need not produce a perfect organism.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Source-documented account of relative fitness, selection and constraints; no selection experiment was recreated.
2026-10-10 · English mechanism checked against Adaptive Evolution's opening account and No Perfect Organism section; deterministic fixation is not asserted.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Heritable differences and environment-dependent reproductive contribution.
Reproductive contribution matters, not survival alone.
Natural selection occurs when heritable differences affect organisms' contributions to later generations. Variants associated with greater reproductive contribution in the relevant environment can become more frequent, producing adaptation under suitable conditions.
Biological evolution is descent with inherited modification. At the population level, a change in allele frequencies across generations is one way to describe evolutionary change; an individual's growth or temporary acclimation is not, by itself, such a change.
Selection is one mechanism that can change inherited population composition.
Calling mutations random with respect to adaptation means that they do not generally arise because their future effect would benefit the organism. It does not mean every DNA site has an equal mutation probability or that mutation rates cannot change with environment. Natural selection instead changes representation through differences in survival and reproduction; inherited variation and its fitness effects depend on context.
Selection filters heritable reproductive differences rather than generating each needed mutation on demand.