Final answer:
Primates have longer juvenile periods to facilitate complex brain development and social learning, which are necessary for their intricate social structures and behaviors.
Step-by-step explanation:
The juvenile period in primates is longer due to their complex social structures, large brains, lengthy gestation periods, and the necessity for extended parental care. Primates, including humans, have evolved to give birth to offspring that are relatively helpless at birth, requiring significant postnatal care. The prolonged juvenile phase allows for an extensive period of learning and brain development, which is important given the intricate behaviors and social dynamics characteristic of primate societies. For example, the cerebrum, which is especially enlarged in primates, is crucial for analyzing sensory information and performing appropriate motor behaviors. Moreover, the social organization of primates, which includes strategizing for resources and relationships, demands a longer period of learning and development.