Maturation is a critical transition in the life cycle. Recent models h
ave used retrospective analyses of patterns of variation in age and si
ze at maturity in an attempt to understand the mechanisms responsible
for generating phenotypic variation in maturation. Empirical work has
revealed greater complexity in the biology of maturation than has been
incorporated in current models, and has cast doubt on some of the ass
umptions and conclusions of the models. Recent insights from experimen
tal work, coupled with theoretical advances for the analysis of growth
, size and other complex characters, have great potential to elucidate
evolution of maturation and how adaptive maturation phenotypes are ac
hieved by real organisms.