Weakness = conflicting research. For example, Rutter et al studied adopted children raised in institutions after the critical period proposed by Bowlby and found that children were able to form secure attachments with their adoptive parents. This shows that the attachment is not with the biological mother, the critical period for attachment is not 2.5 years and can be extended with the right kind of care than suggested. Therefore, this conflicting research weakens the explanatory power of Bowlby’s monotropic theory that there is a critical period for attachment formation.