Final answer:
One notable weakness of John Bowlby's study on attachment is the overemphasis on critical periods, which are rigidly defined times for developing attachments, as opposed to more flexible sensitive periods. Subsequent research, including Mary Ainsworth's Strange Situation study and the case of Genie, have shown that attachment and language acquisition can continue beyond these critical periods, influenced by individual experiences, temperament, and culture.
Step-by-step explanation:
One weakness of John Bowlby's study on attachment is his suggestion of critical periods over flexible sensitive periods. Bowlby's perspective implied an all-or-nothing window of time for forming attachments, which Mary Ainsworth's research contradicted through the Strange Situation procedure. Ainsworth's findings suggested that attachment is not a one-time process fixed in early infancy but is influenced by the child's ongoing experiences and relationships. Furthermore, the case of Genie, a child who missed the critical period for language development due to abuse, highlights another limitation. While Genie acquired a substantial vocabulary, her grammatical abilities remained underdeveloped, possibly due to her inability to learn language during Bowlby's proposed critical period.
Additionally, Bowlby’s critical period hypothesis does not account for the individual differences in children's temperament that can influence attachment styles, as research has shown. This suggests development can be discontinuous and vary greatly among individuals, going against Bowlby's more linear approach to attachment development. Also, cultural differences in attachment, which can defy the one-size-fits-all critical period framework, further illuminate the intricacy of attaching processes beyond Bowlby's initial theory.