Distinguish selection by people from inheritance and trade-offs

Mechanism before a label

Artificial selection occurs when people preferentially breed individuals with chosen traits. It acts on available heritable variation rather than creating a desired allele on demand. A change caused only by better nutrition need not persist when descendants share a common environment.

A response across generations is more persuasive when selected and comparison lineages are reared under matched conditions, with several independently maintained lineages. Measuring many offspring from one lineage does not create many independent selection experiments.

Selecting one trait can change correlated traits because of shared genetic effects or linkage. Reduced diversity and trade-offs can constrain later responses. A historical association between breeding and phenotype is not by itself a controlled estimate of one gene effect.

Predict, compare and calculate

The following record is an original synthetic teaching dataset. Its assigned conditions are not a claim that an actual organism was measured. Write your prediction before revealing the changed condition.

Common-environment trait	Value (trait units)
Selected lineage mean	14
Comparison lineage mean	10

Synthetic descendant means measured in one matched environment.

Your prediction before comparison

This scratch prediction is not saved automatically. Copy it to the lesson notebook to retain it.

Evidence conditionReference comparisonChanged condition / follow-up

Distinguish selection by people from inheritance and trade-offs

Supplied synthetic evidence: Synthetic descendant means measured in one matched environment.

Common-environment trait: reference condition

Quantity	Value	Unit
Selected lineage mean	14	trait units
Comparison lineage mean	10	trait units

Task: Design a paper-only analysis that distinguishes a selected-line response from a seasonal growing-condition change.

Means alone supply neither uncertainty nor a causal mechanism.

Compare with the conditional interpretation

The four-unit contrast is consistent with a selection response but needs lineage replication and ancestry controls.

The lineage contrast is 14−10=4 in the first environment and 18−14=4 in the second. The environmental shift and lineage contrast answer different questions.

Case index for this investigation

0. Connect heritable variation to relative reproductive success
1. Distinguish selection by people from inheritance and trade-offs
2. Separate drift, gene flow and mutation from selection
3. Calculate allele frequencies and test equilibrium claims
4. Combine fossils, homology and molecular evidence
5. Read a longitudinal evolution study without inventing observations
6. Read branching relationships rather than tip order
7. Explain reproductive barriers and divergence
8. Relate variation, changing environments and extinction
9. Separate origin-of-life hypotheses from ancestry evidence

No numerical confidence, laboratory credit or independent mastery is inferred from opening a supplied case. Save your first prediction and comparison in the notebook.

Reset this unsaved comparison

Worked reasoning

The lineage contrast is 14−10=4 in the first environment and 18−14=4 in the second. The environmental shift and lineage contrast answer different questions.

The four-unit contrast is consistent with a selection response but needs lineage replication and ancestry controls.

Apply to a new case

Design a paper-only analysis that distinguishes a selected-line response from a seasonal growing-condition change.

Compare your reasoning with the worked response

Compare descendants from selected and unselected independent lineages in randomized matched environments across the same season. Retain raw line-level records and estimate uncertainty across lineages, not just individual leaves.

This public response supplies feedback, not a score for independent reasoning. Record which part of your prediction changed and why.

Evidence and investigation boundary

Means alone supply neither uncertainty nor a causal mechanism. Parallel mean contrasts do not prove all genetic effects are additive.

For a supervised investigation, predeclare the question, biological unit of replication, treatment/comparison assignment, quantities and units, exclusion rules, graph and uncertainty method. Keep the raw records and the first prediction separate from later revisions. A simulated case does not supply laboratory hours or establish AP authorization. No physical manipulation is required by this lesson.

Source and continuation

Framework topics: 7.3. Current AP Biology framework; supporting scientific reference. Sources checked 30 October 2026; all teaching wording, questions and numbers here are original. Return to AP Biology to compare this mechanism with another scale of organization.