Translating developmental time across mammalian species

Conservation of the order in which events occur in developing mammalian bra ins permits use of regression theory to model the timing of neural developm ent. Following a small adjustment to account for a systematic variability i n primate cortical and limbic systems, the model is used to generate a 95-e vent/nine-species matrix that predicts aspects of neurogenesis and axonal o utgrowth in the brains of developing mice, hamsters, rats, spiny mice, rabb its, ferrets, cats, monkeys, and humans. Although data are compiled from sp ecies in which the timing of birth and the rate of maturation vary widely, the model proves statistically accurate, with practical implications for im proving estimation of milestones of neural development, particularly for hu mans. Using the three-factor model (species, neural events, and primate adjustmen ts), we produce predictions for the timing of 493 neural occurrences in dev eloping mammalian brains that either have not yet been, or cannot be, empir ically derived. We also relate the timing of neural events across the nine species in the form of a reference table calibrated to the development of l aboratory rats. This 'translation' table will assist in attempts to equate the neurodevelopmental literature across species with either large or small differences in gestation and maturation, and also permit studies done in a variety of mammals to be applied to better understand human development. The comparative data indicate that humans, although conventionally consider ed an altricial species, are neurally advanced at birth relative to the oth er species studied. (C) 2001 IBRO. Published by Elsevier Science Ltd. All r ights reserved.