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. T hree related processes, each with their own functional consequences, are im plicated in the alteration of brain development. (1) Maternal undernutritio n 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 res ponse to nutritional stress spares the brain to a large though still limite d degree, reflecting the organ's relative contribution to survival and repr oductive success. (3) Prenatal malnutrition disrupts developing neurotransm itter systems, which results in the expression of specific cognitive and af fective traits. It is argued that the increasing size and therefore cost of the brain, in conjunction with increasing ecological instability and margi nality, reinforced selection for maternally controlled growth suppression o f offspring, reallocation of organ growth rates by offspring, and behaviora l changes related to development of neurotransmitter systems.