The postnatal period in many organisms is a time of extensive growth, during which a variety of anatomical and physiological systems, all requiring substantial investment, develop concurrently. If nutrition is good and other environmental conditions are favorable during this period, then the organism can invest optimally in each of its developing systems. If, to the contrary, nutrition is poor or the organism experiences other environmental stresses such as cold temperatures or exposure to parasites, then the organism may be forced to sacrifice investment in particular developing systems so that investment in others can be maintained. Evolutionary biologists have theorized that in such cases natural selection favors a set of investment priorities, such that systems essential to the individual’s survival will be given first call on resources, whereas other less important systems are sacrificed (Schew & Ricklefs, 1998). Structures used exclusively in sexual display in particular may be given a low priority for investment (Andersson, 1986). The logic here is that an individual with poorly developed display structures that is able to survive has some chance of reproducing, whereas an individual with a welldeveloped display that is unable to survive has none. Neural systems ought to be subject to investment priorities just as are other anatomical and physiological systems. Such priorities therefore provide a framework for interpreting the results of Pravosudov, Lavenex, and Omanska (2005) in this issue. These authors manipulated posthatching nutrition in Western scrub jays (Aphelocoma californica) and tested effects on hippocampal structure and spatial memory. The nutritional manipulation was fairly severe: Experimental birds were limited to 65% of the food intake of controls from the time they were taken from the nest, at about 7 days’ posthatching, until they were able to feed themselves, an ability that developed gradually between 30 and 75 days. Although severe, the restriction is certainly ecologically relevant, as undernutrition of all levels of intensity, up to and including starvation, does occur in nature. At 1 year of age, the nutritionally deprived birds were sacrificed and found to have hippocampal volumes about 8% lower than controls, with approximately 11% fewer neurons. Telencephalon volumes and overall brain masses did not differ between the two groups. Posthatching nutritional restriction in Western scrub jays thus had a lasting negative effect on brain structures that support spatial memory. Behavioral testing demonstrated that the anatomical difference observed between control and experimental birds correlated with a loss of function. At 6