While parental demonstrations of affection are often taken for granted today, there was was a time during the early twentieth century when experts warned parents about the dangers of holding their children. Behaviorist John B. Watson once even went so far as to warn parents, "When you are tempted to pet your child, remember that mother love is a dangerous instrument." According to many thinkers of the day, affection would only spread diseases and lead to adult psychological problems.
However, research on attachment soon changed how we view affection and love. In a series of controversial experiments conducted in 1960s, psychologist Harry Harlow demonstrated the powerful effects of love on normal development. He demonstrated the devastating impact that social isolation had on young rhesus monkeys, which helped researchers better understand just how vital love and affection are for normal childhood development.
Learn more about the study in this article: Harry Harlow and the Nature of Love