There’s that This American Life about it http://www.thisamericanlife.org/radio-archives/episode/317/unconditional-love

scipsy:

[Biology: An Inquiry into the Nature of Life (via Reanimation Library - Catalog)]

Love is a wondrous state, deep, tender, and rewarding. Because of its intimate and personal nature it is regarded by some as an improper topic for experimental research. But, whatever our personal feelings may be, our assigned mission as psychologists is to analyze all facets of human and animal behavior into their component variables. So far as love or affection is concerned, psychologists have failed in this mission. The little we know about love does not transcend simple observation, and the little we write about it has been written better by poets and novelists. But of greater concern is the fact that psychologists tend to give progressively less attention to a motive which pervades our entire lives. Psychologists, at least psychologists who write textbooks, not only show no interest in the origin and development of love or affection, but they seem to be unaware of its very existence.

These are the first lines of the classic paper by Harry F. Harlow: The Nature of Love (1958)

In that paper Harlow describe one of the most fundamental experiment of the history of psychology.

In Harlow’s classic experiment, two groups of baby rhesus monkeys were removed from their mothers. In the first group, a terrycloth mother provided no food, while a wire mother did, in the form of an attached baby bottle containing milk. In the second group, a terrycloth mother provided food; the wire mother did not. It was found that the young monkeys clung to the terrycloth mother whether or not it provided them with food, and that the young monkeys chose the wire surrogate only when it provided food.

Whenever a frightening stimulus was brought into the cage, the monkeys ran to the cloth mother for protection and comfort, no matter which mother provided them with food. This response decreased as the monkeys grew older.

When the monkeys were placed in an unfamiliar room with their cloth surrogate, they clung to it until they felt secure enough to explore. Once they began to explore, they occasionally returned to the cloth mother for comfort. Monkeys placed in an unfamiliar room without their cloth mothers acted very differently. They froze in fear and cried, crouched down, or sucked their thumbs. Some even ran from object to object, apparently searching for the cloth mother, as they cried and screamed. Monkeys placed in this situation with their wire mothers exhibited the same behavior as the monkeys with no mother.

Once the monkeys reached an age where they could eat solid foods, they were separated from their cloth mothers for three days. When they were reunited with their mothers, they clung to them and did not venture off to explore as they had in previous situations. Harlow concluded from this that the need for contact comfort was stronger than the need to explore.

The study found that monkeys who were raised with either a wire mother or a cloth mother gained weight at the same rate. However, the monkeys that had only a wire mother had trouble digesting the milk and suffered from diarrhea more frequently. Harlow’s interpretation of this behavior, which is still widely accepted, was that a lack of contact comfort is psychologically stressful to the monkeys. (via wikipedia)