AgentFarm

Baldwinian vs Lamarckian A/B (Issue #849)

This protocol runs matched intrinsic-evolution sweeps under two inheritance modes to quantify when Lamarckian warm-starting is worth potential stability costs.

Issue: #849

Arms

  • baldwinian: offspring inherit only the hyperparameter chromosome and start with a fresh policy.
  • lamarckian: offspring still inherit chromosome dynamics, and additionally attempt compatible policy warm-start from the parent.

Matrix

  • Profiles: conservative, balanced, buffered
  • Seeds: 42 7 19 101 137 256
  • Total: 2 × 3 × 6 = 36 runs

Held fixed

  • num_steps=1000, warmup_steps=200, snapshot_interval=50
  • Mutation: gaussian, mutation_rate=0.15, mutation_scale=0.10, boundary mode reflect
  • Crossover disabled (to isolate inheritance mode)
  • selection_pressure=low
  • Initial diversity: independent mutation (rate=1.0, scale=0.25)
  • Speciation: GMM, max_k=4

Run commands

Note: Results under experiments/inheritance_ab_pre_fix/ were collected before a decision-path fix (2026-05-22) that prevented policy weights from influencing actions. That aggregate is invalid; use a fresh output directory after the fix lands.

1) Run both arms

PYTHONHASHSEED=0 python scripts/run_inheritance_mode_ab.py \
  --output-dir experiments/inheritance_ab \
  --disk-database \
  --resume

2) Compare paired deltas (treatment vs Baldwinian baseline)

python scripts/compare_inheritance_arms.py \
  --baseline-dir experiments/inheritance_ab/baldwinian \
  --baseline-label baldwinian \
  --treatment-dir experiments/inheritance_ab/lamarckian \
  --arm-labels lamarckian \
  --output-dir experiments/inheritance_ab/aggregate

Outputs

  • experiments/inheritance_ab/inheritance_ab_manifest.json
  • Per-arm sweep_manifest.json and stable-profile analysis artifacts
  • experiments/inheritance_ab/aggregate/inheritance_ab_summary.json
  • experiments/inheritance_ab/aggregate/inheritance_ab_summary.md
  • experiments/inheritance_ab/aggregate/paired_delta_heatmap.png
  • experiments/inheritance_ab/aggregate/speciation_trajectories_with_arms.png
  • experiments/inheritance_ab/aggregate/startup_transient_comparison.png

Acceptance criteria

Use paired-seed deltas (treatment - baseline) with:

  • 95% CI excluding zero, and
  • sign agreement >= 75%

Primary readouts:

  • Performance: population_mean, population_final
  • Stability: startup_transient.peak_death_rate, startup_transient.oscillation_amplitude, lineage.churn_rate
  • Diversity impact: speciation_final, speciation_slope
  • Mechanism coverage: warmstart_rate, gate_hit_rate (P4), blend_alpha (P4)

Per-profile recommendation categories (label-aware):

  • net recommend <treatment-label> (e.g. net recommend lamarckian)
  • net recommend <baseline-label> (e.g. net recommend baldwinian)
  • performance win + stability loss
  • speciation collapse risk
  • no robust effect

The classifier consults the metric groups documented above:

  • Performance: population_mean, population_final
  • Stability loss: startup_transient.peak_death_rate, startup_transient.oscillation_amplitude, lineage.churn_rate
  • Speciation collapse: robust negative delta on speciation_slope