Final answer:
The sensitive period for language acquisition in childhood is the best known example of a critical period in development.
Step-by-step explanation:
The best known example of a critical period in development is the sensitive period for language acquisition in humans. This is a specific time period during childhood when children are most receptive to learning language. If a child is not exposed to language during this critical period, they may have significant difficulty acquiring language later in life.
For example, the case of Genie, a girl who was isolated and abused during her early childhood, provides evidence for the existence of a critical period for language acquisition. Despite receiving intensive language instruction after being rescued, Genie struggled to develop linguistic skills to a level consistent with her chronological age.