Attachment theory proposes that strong emotional bonds form between infants and their caregivers and that these bonds are important for survival. John Bowlby was the first major theorist of attachment, suggesting infants become attached to caregivers who are sensitive and responsive in order to feel safe and secure as they grow. Bowlby described four stages of attachment from birth through early childhood and proposed that attachment behaviors evolved to promote survival. Further research identified different styles of attachment in children, including secure, avoidant, ambivalent, and disorganized attachment.