Predicting the Timing of Critical Periods in Development

Critical periods are specific periods in the development of a living organism during which there is an increased sensitivity to external perturbations. Such perturbations result in a developmental trajectory significantly different from what is considered the norm. This paper is concerned with the question of whether the presence and timing of a critical period can be predicted from the developmental profile without perturbation. Taking rate of change as a measure of this profile, we put forward the hypothesis that critical periods will occur when the rate of change is greatest. Using a simplified model of differential gene expression, cellular mechanics and evolution, we evolve organisms with different developmental profiles, test the presence of critical periods by systematically exposing the developing system to an external perturbation at different times between runs, and correlate the timing of these critical periods with the proposed developmental measure. We discuss the implications of our findings.