Explain adaptation through inherited variation

Adaptation requires inherited variation and generations

Natural selection changes the representation of inherited variants when they contribute differently to later generations. An individual does not acquire a needed inherited variant simply because conditions become difficult. Mutation can introduce variation, gene flow can move it, and drift can change frequencies by chance. Selection acts on existing differences in survival and reproduction in a particular environment.

An adaptation is context-dependent. A trait that helps under one condition may be costly under another. A population can fail to track rapid environmental change if suitable variation, population size, dispersal or generation time constrains its response. Evolution is not a guarantee against extinction.

Normalize reproductive contributions

The original lab uses a simplified haploid population with variants A and a. Initial A frequency is p. Relative reproductive contribution is wA for A and 1 for a. The next-generation frequency is p′=p wA/[p wA+(1−p)]. This is a deterministic expectation with no mutation, migration or drift.

At p=0.5 and wA=1.5, A contributes 0.75 relative units and a contributes 0.5. Total contribution is 1.25, so p′=0.75/1.25=0.6. The unnormalized 0.75 is not a frequency. The alternative still contributes descendants, so a favorable A does not instantly become universal.

At wA=1, both variants contribute equally and p′=p. At wA=2 with p=0.5, p′=1/1.5, about 0.667. The gain is conditional on inherited differences and the assigned environment. A changed environment can change the relative contributions, which the one-generation comparison does not predict.

Distinguish selection from other explanations

An observed increase in a trait is not automatically evolutionary adaptation. Individuals might acclimate, the sampled age structure might change, migrants might arrive or observers might change methods. To support selection on inherited variation, seek evidence about inheritance, reproductive contributions and changes across generations.

Small populations can deviate markedly from deterministic expectations because only a finite sample of offspring forms the next generation. This model deliberately excludes that drift. A numerical discrepancy therefore need not falsify inheritance; it may reveal an omitted process or measurement uncertainty.

Transfer and environmental change

Consider initial A frequency 0.1 with wA=2. The next frequency is 0.2/(0.2+0.9), about 0.182. Starting from 0.9 with the same advantage gives 1.8/(1.8+0.1), about 0.947. Both increase, but neither reaches one in a single generation. Explain why initial variation affects the trajectory.

A proposed conservation action claims a population will “learn to tolerate” a new stress and pass that tolerance on. Rewrite it as testable alternatives: within-lifetime acclimation, selection on inherited variation, or movement to suitable habitat. Identify evidence needed for each and why the original wording conflates them. No breeding or organism exposure is required for this virtual investigation.

Source scope and evidence boundary

Original explanation, synthetic data and practice aligned with AP Environmental Science topic 2.6. Framework checked 30 October 2026: official topic map and Fall 2026 clarifications. The adaptation wording distinguishes inherited population changes over generations from individual need. Public numerical feedback is not independent assessment; virtual captures do not establish supervised fieldwork or actual ecosystem outcomes.