The Marginalian
The Marginalian

The Nature of Love: How Harry Harlow’s Seminal 1958 Research Shaped the Science of Affection and Changed Modern Parenting

The Nature of Love: How Harry Harlow’s Seminal 1958 Research Shaped the Science of Affection and Changed Modern Parenting

“To love without knowing how to love wounds the person we love,” the great Zen teacher Thich Nhat Hahn wrote in his insightful treatise on mastering the art of “interbeing.” Nowhere is this wounding potential of unskillful love more palpable, nor more scarring, than in our formative relationships to the caretakers who first loved us, which lay the foundation for our lifelong attachment patterns. But as elemental as these early building blocks of love may be, our understanding of them is rather nascent and much of it can be traced to the work of primate researcher Harry Harlow (October 31, 1905–December 6, 1981), whose trailblazing studies of young rhesus monkeys were instrumental in our present undertanding of love, attachment, and good parenting.

In 1958, Harlow was elected president of the American Psychological Association. At the APA’s annual meeting on August 31 of that year, he delivered a seminal paper titled “The Nature of Love,” cited in Love at Goon Park (public library) — Deborah Blum’s masterful chronicle of how Harlow pioneered the science of affection.

Harry Harlow observes a baby monkey interact with the cloth mother
Harry Harlow observes a baby monkey interacting with a cloth mother

An important call for nuance and context here: While some of Harlow’s studies on monkeys are controversial and even morally unacceptable by our present standards, we must not forget that he was abiding by his own era’s standards, which were radically different from ours in innumerable realms of life. (To wit: In the same period, computing pioneer Alan Turing was prosecuted by the government for being homosexual and ultimately met his death in consequence — a failure of human rights so profound and violent that it puts any discussion of animal rights in perspective.) By and large, societies only ever fine-tune their moral standards after facing the discomfort of their own cruelties. So cruelty that we perceive in some of Harlow’s studies today is the very reason we’ve come to change our standards for what is acceptable in animal research. We must, then, resist the self-righteous temptation of judging a previous era by the standards of a subsequent one. Only then can we fully grasp the significance of Harlow’s research and the long tail of his enormous contribution to social science.

For instance: I grew up in Eastern Europe, where caretaking at orphanages and mental institutions was nothing short of savage well into the beginning of the twenty-first century, in large part due to a grave systemic ignorance about the lifesaving power of touch and creaturely contact — the very subject of Harlow’s studies. When things finally began to shift, slowly and painfully, the small but passionate caucus of activists relied heavily on Harlow’s research to overturn deadly policies. It is hard to estimate how many children’s lives have been transformed or downright saved due to those changes, but I would imagine that in Bulgaria alone, a small country of barely six million, the count is by now in the thousands.

One of Harlow's baby rhesus monkeys with its wire-and-cloth mother
One of Harlow’s baby rhesus monkeys with its wire-and-cloth mother

With this essential context, Harlow’s 1958 paper on the nature of love stands as the flag of a monumental revolution in psychology and social science, which has reverberated across everything from policy to parenting. He writes:

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.

Rebuking his peers for having made no systematic effort to study love despite its centrality to the human experience, he adds:

Thoughtful men, and probably all women, have speculated on the nature of love. From the developmental point of view, the general plan is quite clear: The initial love responses of the human being are those made by the infant to the mother or some mother surrogate. From this intimate attachment of the child to the mother, multiple learned and generalized affectional responses are formed.

To better understand the types of affectional attachments that make infants thrive or perish, Harlow’s lab had just begun studying the effects of various mothering methods and environments on the development of young rhesus monkeys. He reports:

We [found] that a baby monkey raised on a bare wire-mesh cage floor survives with difficulty, if at all, during the first five days of life. If a wire-mesh cone is introduced, the baby does better; and, if the cone is covered with terry cloth, husky, healthy, happy babies evolve. It takes more than a baby and a box to make a normal monkey. We were impressed by the possibility that, above and beyond the bubbling fountain of breast or bottle, contact comfort might be a very important variable in the development of the infant’s affection for the mother.

But the most dramatic effects came from the type of artificial surrogate mother assigned to the baby monkeys — either a “mother” made solely of wire, resembling the metal skeleton of a doll, or one made of wire padded with soft materials and illuminated from the inside to simulate bodily warmth. Despite the fact that the wire-only mother held a milk bottle and provided sustenance to the babies, and the wire-and-cloth mother did not, the infants consistently chose the warm and cuddly mother over the cold food-dispensing one.

One of Harlow's baby monkeys displaying the consistent choice of cloth mother over wire mother
One of Harlow’s baby monkeys displaying the consistent choice of cloth mother over wire mother

Harlow offers a sad account of the results — sad only in that it shines a sidewise gleam on our greatest human longings and the perennial tragedy of how imperfectly they are met by the imperfect human beings to whom we turn for love, be they parents or partners:

The surrogate was made from a block of wood, covered with sponge rubber, and sheathed in tan cotton terry cloth. A light bulb behind her radiated heat. The result was a mother, soft, warm, and tender, a mother with infinite patience, a mother available twenty-four hours a day, a mother that never scolded her infant and never struck or bit her baby in anger.


One control group of neonatal monkeys was raised on a single wire mother, and a second control group was raised on a single cloth mother. There were no differences between these two groups in amount of milk ingested or in weight gain. The only difference between the two groups lay in the composition of the feces, the softer stools of the wire-mother infants suggesting psychosomatic involvement. The wire mother is biologically adequate but psychologically inept.

And yet the magnitude of the rift between biological and psychological comfort surprised even the researchers themselves. Harlow writes:

We were not surprised to discover that contact comfort was an important basic affectional or love variable, but we did not expect it to overshadow so completely the variable of nursing; indeed; indeed, the disparity is so great as to suggest that the primary function of nursing as an affectional variable is that of insuring frequent and intimate body contact of the infant with the mother. Certainly, man cannot live by milk alone. Love is an emotion that does not need to be bottle- or spoon-fed, and we may be sure that there is nothing to be gained by giving lip service to love.


These data make it obvious that contact comfort is a variable of overwhelming importance in the development of affectional response, whereas lactation is a variable of negligible importance.

More than a quarter century before the first scientific paper published in stanzaic form, Harlow — a lover and writer of poetry — included in his paper the sweet and fun-loving touch of illustrated verses about the importance of contact comfort in the animal kingdom:



The rhino’s skin is thick and tough,
And yet this skin is soft enough
That baby rhinos always sense,
A love enormous and intense.



This is the skin some babies feel
Replete with hippo love appeal.
Each contact, cuddle, push, and shove
Elicits tons of baby love.



Though mother might be short on arms,
Her skin is full of warmth and charms.
And mother’s touch on baby’s skin
Endears the heart that beats within.



Here is the skin they love to touch.
It isn’t soft and there isn’t much,
But its contact comfort will beguile
Love from the infant crocodile.



To baby vipers, scaly skin
Engenders love ‘twixt kith and kin.
Each animal by God is blessed
With kind of skin it loves the best.


But Harlow’s most prescient point has to do with the implications of these findings for equal parenting, particularly for modern fatherhood. Writing in 1958 — a time when women began leaving the home and entering the workforce, thus changing the social structure of motherhood without proper recompenses in fatherhood — Harlow presages a future in which we are still struggling to navigate these issues and makes a beautiful case for affectionate fatherhood:

If this process continues, the problem of proper child-rearing practices faces us with startling clarity. It is cheering in view of this trend to realize that the American male is physically endowed with all the really essential equipment to compete with the American female on equal terms in one essential activity: the rearing of infants. We now know that women in the working classes are not needed in the home because of their primary mammalian capabilities; and it is possible that in the foreseeable future neonatal nursing will not be regarded as a necessity, but as a luxury [or] a form of conspicuous consumption limited perhaps to the upper classes. But whatever course history may take, it is comforting to know that we are now in contact with the nature of love.

For a deeper dive into Harlow’s pioneering research and lasting legacy, see Blum’s terrific Love at Goon Park, then revisit sociologist Eva Illouz on the sociology of why love hurts, philosopher Skye Cleary on why we love, and these five excellent books on the psychology of love.

Published August 31, 2016




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