Modeling developmental plasticity in human growth: Buffering the past or predicting the future?

Abstract

Substantial variation in adult body size between human populations is widely assumed in part to represent adaptation to local ecological conditions. Developmental plasticity contributes to such variability; however, there is debate regarding how this early-life process can produce adaptation when environments change within the life span. We developed a simple mathematical simulation model, testing how human fetuses could tailor their growth to ecological conditions without being oversensitive and hence prone to extremes of growth. Data on Indian rainfall (1871-2004) were used as an index of ecological conditions. The simulation model allowed the comparison of different strategies for processing these time-series data regarding (a) the toleration of short-term ecological variability and (b) the prediction of conditions in adulthood. We showed that ecological information processing is favored in environments prone to long-term ecological trends. Once this strategy is adopted, resistance to shortterm ecological perturbations can be achieved either by lengthening the duration of developmental plasticity or by accumulating multigenerational influences. A multigenerational strategy successfully dampens the transmission of the effects of ecological shocks to future generations, but it does not predict or enable offspring to respond to longer-term conditions. However, this strategy does allow fetal growth to be tailored to the likely supply of nutrition from the mother in the period after birth, during when extrinsic mortality risk is high. Our model has implications for public health policies aimed at addressing chronic malnutrition.