GROWING NEURAL NETWORKS Growing neural networks are networks which are constructed by executing genetic instructions contained in a genotype. These instructions and their products interacts non-linearly to eventually determine the mature structure. We present simulations in which the mapping from genotype to phenotype is instantaneous and simulations in which it develops in time during a segment of an individual's lifetime, i.e. the individual's developmental age, allowing us to study both neural evolution and neural development. The results shed some light on (a) why modular architectures are likely to emerge, (b) why similar successions of stages tend to appear in both evolution and development, and (c) why a developmental age is preserved evolutionarily although the mature state may appear to be more efficient from the point of view of fitness.