Separate phenotype sorting from an inherited response

1. Orient: Separate phenotype sorting from an inherited response

Phenotypes can vary because of inherited differences, environmental differences and their interactions. Selection can associate a phenotype with contribution to offspring, but a next-generation response also depends on what is transmitted. A changed phenotype mean under a changed environment is not by itself evolutionary genetic change.

2. Explain the population mechanism

Four equally frequent original phenotype classes1,2,3,4 have initial mean2.5. Contribution weights are1+s(z−2.5), with the supported slope keeping every weight positive. The selected-parent mean is the weighted sum of phenotype divided by total weight; subtract2.5 to obtain the selection differential.

The model multiplies this differential by a supplied inherited-response coefficient between0 and1. That coefficient is a pedagogical assumption, not an estimate of heritability from the four weights. The same observed sorting can predict different offspring means when the transmitted component differs. Real quantitative-genetic inference needs an appropriate design and assumptions about genetic/environmental covariance.

Directional, stabilizing and disruptive selection describe different phenotype-contribution patterns. This particular linear weight model represents only directional sorting; it does not demonstrate that natural selection always reduces variance or produces perfect adaptation. Tradeoffs, constraints and changing environments can prevent a single optimum. Use independent common-environment and family evidence rather than interpreting a correlation as a complete mechanism. For the same four phenotype classes, symmetric weights1,3,3,1 favor intermediate classes (stabilizing sorting); weights3,1,1,3 favor extremes (disruptive sorting). Both keep the selected mean2.5, but their weighted variances are0.75 and1.75 compared with the original1.25. Therefore an unchanged mean can conceal strong phenotype-dependent contribution. Predict which pattern reduces the selected-parent spread before calculating; the stabilizing record does, but inheritance and next-generation environmental effects remain separate.

3. Work a complete evidence calculation

At slope0.2, weights are0.7,0.9,1.1,1.3, summing4. Weighted phenotype sum11 gives selected mean2.75 and differential0.25. With supplied response coefficient0.5, response0.125 predicts offspring mean2.625 under the unchanged-baseline assumption.

4. Predict and investigate

Predict first: Would strong phenotype sorting guarantee the same response if the sorted differences were entirely environmental?

Hold slope0.2 while changing the response coefficient from0 to1. Retain selected-parent and offspring means separately. Design a common-environment comparison and name a remaining maternal or shared-environment alternative it would not automatically remove.

Retain the original population definition, first prediction, controls and full numerical ledger, including conflicting or null results. These are original bounded teaching calculations, not measured populations.

5. Transfer and explain

Apply the mechanism to a changed case

At slope0.4 and response coefficient0.25, calculate selected mean, differential and offspring mean.

Retain your calculation, units and assumptions in the lesson notebook before opening this public practice response.

Compare a worked response

Weights0.4,0.8,1.2,1.6 give weighted sum12/total4=3. Differential0.5 and response0.125 give offspring mean2.625. Equal predicted offspring means can arise from different sorting/transmission combinations.

6. Reflect and retain evidence

State a competing mechanism, an observation that would distinguish it, and a limitation of the supplied sampling or life-cycle model. Preserve first reasoning and a criterion-linked human review in the General Biology II workspace. Public practice feedback and simulated evidence do not certify an independently demonstrated comparative argument, field investigation or practical skill.

Supporting scientific reference, checked 30 October 2026. All prose, numerical packets and diagrams are original. No organism collection, culture, breeding, release, personal genetic inference or clinical procedure is requested.