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PredPreyGrass

A Concrete Eco-Evolutionary Analogue​

PredPreyGrass gives a concrete simulation analogue for the general distinction between Darwinian selection, Baldwinian interaction, and artificial Lamarckian inheritance.

The general distinction is still the same: what matters is what crosses the generational boundary.

Diagram comparing Lamarckian inheritance, Darwinian evolution, the Baldwin effect, and Waddington's genetic assimilation
Display 1: Lamarckian inheritance passes acquired change directly, while the Baldwin effect lets learned behavior guide selection without direct inheritance of that learned behavior. Image by Ian Alexander, CC BY-SA 4.0.

In predpreygrass.eco_evolutionary, the active heritable trait is a speed genome. Offspring inherit the parent's speed genome with bounded mutation. The learned PPO policy weights are not part of the inherited genome in the base experiment.

In predpreygrass.eco_evolutionary_cadence, speed controls movement frequency rather than movement distance. The policy can observe both the agent's speed and whether movement is available on the current step. This makes the Baldwinian mechanism especially explicit: inherited speed changes the body-environment interface, learning can condition behavior on that inherited trait, and ecological success determines which genomes reproduce.

Diagram of the PredPreyGrass Baldwinian loop where inherited speed genomes shape movement, learned policy behavior affects ecological fitness, and offspring inherit mutated genomes rather than acquired policy weights
Display 2: PredPreyGrass as a Baldwinian loop: inherited speed genomes shape movement mechanics, learned behavior changes ecological success, and offspring inherit mutated genomes rather than acquired policy weights.

Interpretation​

MechanismWhat is learned during lifeWhat is inheritedPredPreyGrass interpretation
BaldwinianBehavior or policy improves through experience.Parameters that support learning, not the acquired behavior itself.Best fit for the base eco-evolutionary speed-genome experiments.
LamarckianBehavior, policy weights, or acquired parameter state changes through experience.The acquired state itself is copied into descendants or replacement populations.Closest fit for variants with policy cloning, continued weights, or PBT-style copying.
Darwinian selection without learningNo within-lifetime policy learning is required.Heritable traits vary and are filtered by reproductive success.Baseline when speed affects movement and fitness, but policy behavior is blind to the genome.
Display 3: PredPreyGrass changes interpretation depending on whether only the genome is inherited or learned policy state is copied forward.