In the genus Macaca, represented by seven species, neonatal weight scales at a power of maternal weight of a = 0.49. This value is lower than those for subordinal and ordinal scaling of neonatal weight in primates (a = 0.63–0.78), but it is higher than the value for intrageneric scaling of brain weight in Macaca (a = 0.18). A causal interpretation is attempted for differing values of a at different taxonomic levels and between different organ systems.