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The Baldwin Effect Reloaded: Intermediate Levels of Phenotypic Plasticity Favor Evolutionary Rescue.
The American Naturalist
|October 31, 2025
Summary
Phenotypic plasticity can aid evolutionary rescue by allowing populations to adapt to new environments. The "original Baldwin effect" is a genuine evolutionary mechanism, but its strength depends on the level of plasticity.
Area of Science:
- Evolutionary biology
- Theoretical ecology
- Genetics
Background:
- The interplay between phenotypic plasticity and genetic adaptation has been debated since the late 1890s.
- The "original Baldwin effect" (OBE) posits plasticity aids populations in altered environments, allowing genetic evolution to follow.
- Conversely, the "Mayr effect" (ME) suggests plasticity can slow evolution by masking genetic variation.
Purpose of the Study:
- To resolve the verbal and qualitative opposition between OBE and ME using a quantitative model.
- To investigate the conditions under which phenotypic plasticity promotes or hinders evolutionary rescue.
- To model the effects of extinction, selection, mutation, and plasticity on population survival and adaptation.
Main Methods:
- Development of a stochastic model incorporating extinction, selection, mutation, and plasticity.
- Quantification of phenotypic plasticity as the probability (p) of a maladapted genotype developing the adapted phenotype.
- Analysis of evolutionary rescue, defined as the arrival and invasion of an adaptive genetic mutant in a new environment.
Main Results:
- The original Baldwin effect (OBE) is a genuine evolutionary mechanism, contingent on a plasticity threshold (p*).
- Below the threshold (p < p*), increased plasticity ("strong" OBE) delays extinction and promotes evolutionary rescue.
- Above the threshold (p > p*), plasticity has dual effects: "weak" OBE accelerates adaptation (intermediate p), while ME slows it (high p) by reducing fitness advantages.
Conclusions:
- Phenotypic plasticity plays a critical role in evolutionary rescue, with its impact modulated by the level of plasticity.
- A threshold in plasticity determines whether it primarily facilitates survival or influences the speed and mode of adaptation.
- The study provides a quantitative framework for understanding the complex relationship between phenotypic plasticity and genetic evolution.
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