Attachment is an emotional bond between an infant and caregiver that develops through proximity seeking and distress upon separation. Several theories emerged to explain attachment, including learning theories that proposed it develops through conditioning, as well as evolutionary theories that view it as an innate mechanism for survival. Key studies include Ainsworth's Strange Situation experiment, which identified secure, avoidant, and resistant attachment styles in infants. Research on the effects of deprivation found that early privation can negatively impact relationships, but recovery is possible if attachment is formed later in the critical period. Studies on day care quality, effects, and relationships have yielded mixed results, with higher quality care associated with better cognitive outcomes but potential risks for aggression depending on other factors like secure attachment.