Leo is a 6-month-old infant. Whenever his mother, Elena, approaches him, Leo begins to smile, coo, and reach out his hands. Elena finds these behaviours impossible to ignore and immediately responds by picking him up, cuddling him, and speaking in a high-pitched voice. On the other hand, Leo's father, Marcus, is responsible for most of the feeding. Leo has quickly learned to associate Marcus with receiving milk, and now begins to gurgle happily as soon as he hears Marcus preparing a bottle in the kitchen.

Discuss both learning theory and Bowlby's monotropic theory as explanations of attachment. Refer to Leo, Elena, and Marcus in your answer.