Theory 030/Life & Evolution /Evolutionary developmental biology
Plasticity Comes Before Genes
Assimilation is described as genes catching up with a plastic trait. The catching up may require a predictable world.
Phenotypic plasticity precedes genetic assimilation at a threshold of environmental predictability, so a trait should appear first as a plastic response and become fixed only when the environment is reliably predictive.
01The evidence
Genetic assimilation has been demonstrated in laboratory populations exposed to repeated environmental challenges, with the trait becoming constitutive over generations.
02The tension
Assimilation is treated as a general consequence of selection on a plastic trait, which predicts it should occur whenever the trait is favoured. It is not always observed.
03The mechanism
A plastic response is only worth making constitutive if the environment reliably calls for it. If the cue is unreliable, a constitutive response would be wrong half the time, so selection keeps the response plastic.
That makes predictability the threshold, and predicts assimilation should occur only when the cue predicts the environment above a certain accuracy.
04What this is not
That view predicts fixation whenever the trait is favoured. This predicts fixation only when the cue is reliable.
05Predictions
- P1Assimilation should occur only above a cue-reliability threshold.
- P2Unreliable cues should preserve plasticity.
- P3Restoring reliability should restart assimilation.
06Refutation
Assimilation occurring regardless of cue reliability would leave the unconditional account adequate.
07What it changes
It would make plasticity evolution predictable from environmental statistics.