Evolution of sensitive periods in development
Sensitive periods are widespread in nature. Despite a recent focus on neural-physiological explanation, few formal models have examined the evolutionary selection pressures that produce sensitive periods. Here, we review the current set of models, including our own work. We have modeled development as a specialization process during which individuals incrementally adapt to local environmental conditions, while collecting a constant stream of cost-free, imperfect cues to the environmental state. We compute optimal developmental programs across a range of ecological conditions and use these programs to simulate developmental trajectories and obtain distributions of mature phenotypes. We highlight four main results. First, matching the empirical record, sensitive periods often result from experience or from a combination of age and experience, but rarely from age alone. Second, individual differences in sensitive periods emerge as a result of stochastic sampling: individuals who sample more consistent cue sets lose their plasticity at faster rates. Third, in some cases, experience during a sensitive window shapes phenotypes only at a later life stage (lagged effects). Fourth, individuals might perseverate along developmental trajectories despite accumulating evidence suggesting the alternate trajectory is more likely to match the ecology.
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