Evolutionary and ecological aspects of early brain malnutrition in humans.

This article reviews the effects of malnutrition on early brain development using data generated from animal experiments and human clinical studies. Three related processes, each with their own functional consequences, are implicated in the alteration of brain development. (1) Maternal undernutrition at the start of pregnancy results in reduced transfer of nutrients across the placenta, allowing the conservation of effort for future reproductive episodes. (2) Differential allocation to growing organs by the fetus in response to nutritional stress spares the brain to a large though still limited degree, reflecting the organ's relative contribution to survival and reproductive success. (3) Prenatal malnutrition disrupts developing neurotransmitter systems, which results in the expression of specific cognitive and affective traits. It is argued that the increasing size and therefore cost of the brain, in conjunction with increasing ecological instability and marginality, reinforced selection for maternally controlled growth suppression of offspring, reallocation of organ growth rates by offspring, and behavioral changes related to development of neurotransmitter systems.