Final answer:
Harry Harlow's work showed that infant attachment is not just based on nourishment but also on comfort and security. John Bowlby built on Harlow's findings with attachment theory, focusing on the caregiver's responsiveness and the quality of interactions. Subsequent research has considered additional factors like temperament and culture in the formation of attachment.
Step-by-step explanation:
Harry Harlow’s studies on the formation of infant attachment in monkeys during the 1950s and 1960s were pioneering for understanding social and emotional development. Harlow found that social comfort was more critical to attachment than just providing nourishment. He provided monkeys with two surrogate mothers; one was a wire mesh mother with food, and the other was a cloth mother offering no food. The monkeys showed a preference for the soft terrycloth mother, thus emphasizing the importance of comfort and security in attachment formation. This challenged the then-prevailing idea that attachment was primarily about nourishment. John Bowlby expanded on this understanding by developing attachment theory, which emphasized the need for a responsive caregiver and mutually enjoyable interactions as the basis for a healthy attachment. Later research by Ainsworth and others built on and also critiqued this work, considering the roles of temperament and cultural factors in attachment.