The Harlow experiment that demonstrated the power of love (LAUREN SLATER)

The Harlow experiment that demonstrated the power of love (LAUREN SLATER)

Harry Harlow’s experiments with wire monkeys are central demonstrations in the psychology of attachment. Harlow was able to show that infant monkeys cared more for a soft surrogate mother than a metal milk-bearing one, and with this finding, a whole science of touch was born. His experiments, many captured on film, are chilling and underscore the power of proximity in our lives.

When Harlow came to Madison, he planned to study rats, but he wound up with monkeys, rhesus monkeys, a small agile breed. Ever Terman’s student, he began by devising a test of monkey intelligence, a sort of simian IQ profile, and he was extremely successful at proving that these little primates could solve problems in ways far more complex than prior primate researchers had ever thought. His reputation rose. Madison gave him an old box factory for a primate lab, and students sought him out. When studying the monkeys, Harlow would separate the infants from their mothers and peers, and this is how he stumbled into fame. He was studying the monkey head, but he observed the monkey heart, and he wondered. The infant monkeys, when separated, became extremely attached to the terry cloth towels covering the cage floors. They would lie on them, grip them in their tiny fists, tantrum if they were taken away, just like a human infant with a ratty blanket or a stuffed bear. The monkeys loved these towels. Why? This was a huge question. Attachment had previously been understood in terms of nutritive rewards. We love our mothers because we love their milk. A baby clings to its mother because it sees the swollen breasts, the tan aureole and the nub of nipple rising from its pleated folds, and it feels thirst or hunger. Kenneth Hull and Clark Spence themselves had said all of human attachment is predicated on drive reduction: hunger is a primary drive and we want to reduce it; so are thirst and sex. From the 1930s through the 1950s, the theory of drive reduction and its link to love went unquestioned.

Harlow, however, began to question it. He fed the baby monkeys by hand, with little plastic bottles, and when he took the bottles away, the infants just smacked their lips and maybe wiped a white dribble off their hairy chins. But when Harlow tried to take the terry cloth towels away, well, the simians screamed like a slaughterhouse, throwing their small bodies down and clutching at bunches of cloth. This fascinated Harlow. The simians screamed. (Somewhere else, in another time, Mabel had stood by the window, her son just two feet from her plush but cool side. Animals flew in a personal forest, slashed with black lines, bleeding blue and red.) He watched the monkeys scream and thought love. What is love? Then Harlow saw. As his biographer Blum writes, the best way to understand the heart, was to break it. And so started his brutal and beautiful career.

Rhesus macaque monkeys share roughly ninety-four percent of their genetic heritage with humans. Another way to put this is that humans are ninety-four percent rhesus macaque monkey, six percent people. Moving up the phylogenetic scale, we are approximately ninety-eight percent orangutan or approximately ninety-nine percent chimpanzee, with just the barest fleck of flesh as solely human. This is precisely why psychological researchers have long gravitated toward the use of primates in their experiments. Says primate researcher Roger Fouts, “Monkeys have a whole repertorie of language, an entire, complex intelligence that we fail to value only because of our Cartesian view of the world.” Obvious to Fouts, maybe, but not to Harlow, who said, “The only thing I care about is whether a monkey will turn out a property I can publish. I don’t have any love for them. I never have. I don’t really like animals. I despise cats. I hate dogs. How could you love monkeys?”

The experiment required wire cutters, cardboard cones, hot coils, steel nails, and soft cloth. Harlow used the wire cutters to fashion a wire mother, its torso patterned with small squares everywhere, a single inflexible breast “on the ventral front.” Affixed to this breast, a steel nipple pierced with a tiny hole through which the monkey milk could flow.

Then, Harlow fashioned a soft surrogate, a cardboard cone bunted in a terry cloth towel.

We designed the mother surrogate in terms of human-engineering principals… We produced a perfectly proportioned, streamlined body stripped of unnecessary bulges and appendages. Redundancy in the surrogate mother’s system was avoided by reducing the number of breasts from two to one and placing this unibreast in the upper thoracic sagittal position, thus maximizing the natural and known perceptual and motor capabilities of the infant operator… the result was a mother, soft, warm, and tender, a mother with infinite patience, a mother available 24 hours a day… furthermore we designed a mother-machine with maximal maintenance efficiency since failure of any system or function could be resolved by simple substitution of black boxes and new component parts. It is our opinion that we engineered a very superior monkey mother, although this position is not held universally by monkey fathers.

So, they started. They took a group of newborn rhesus macaque babies and put them in the cage with the two surrogate mothers: the wire mother full of food, the cloth mother with an empty breast and a sweet smile. Lab assistants’ notes detail the trauma of the experiment: the real mother macaques, realizing their babies were being stolen, screaming and banging their head against the cage; the infants choo-chooing as they were hurled into a separate space. Hour after hour this animal fear going on, and the lab filled with the stench of it, anxious scat, soft stools indicating, Harlow writes, high emotionality. The cages were smeared gold with grief, the infant macaques all balled over themselves with their tails held high to show their tiny oozing anuses.

But then, Harlow observed something amazing start to happen. Within a matter of days, the baby macaques transferred their affections from the real mother, who was no longer available, to the cloth surrogate mother, to whom they clung, over whom they crawled, manipulating her face in their miniature hands, biting her gently, spending hours upon hours on her belly and back. The cloth mother, however, had no milk, so when the youngsters were hungry, they would scamper off, dart over to the steel mammary machine—the chicken-wire mother—and then, having had their fill from the fountain, run back to the safety of the soft towel. Harlow graphed the mean amount of time the monkeys spent nursing versus cuddling, and his heart must have pattered fast, for he was on the brink of discovery, and then he was over discovery’s edge. “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, the disparity is so great as to suggest that the primary function of nursing . . . is that of insuring frequent and intimate body contact of the infant with the mother.”

Here Harlow was establishing that love grows from touch, not taste, which is why, when the mother’s milk dries up, as it inevitably does, the child continues to love her, and then the child takes this love, the memory of it, and recasts it outward, so that every interaction is a replay and a revision of this early tactile touch. “Certainly,” writes Harlow, “man cannot live by milk alone.”

The 1930s to 1950s was a cold era in childrearing. The famous pediatrician Dr. Benjamin Spock advised feeding by schedule; Skinner understood the infant in terms of its prior patterns of reinforcement and punishment, so that if you wanted to stop a baby from crying, you were to stop rewarding it by picking it up. Nestlé and Ross laboratories discovered formula, white powder, plastic nipples, tepid water from the faucet. John Watson famously wrote, in his books about how to rear children, “Do not overindulge them. Do not kiss them goodnight. Rather, give a brief bow and shake their hand before turning off the light.”

Well, Harlow was going to take all that dreck to the dreck bin and replace it with the REAL truth, which was that you should never shake a baby’s hand. You should not hesitate to hold him. Touch is critical, not a spoiler but a saver; however, the good news is, any old palm will do. “Love for the real mother and love for the surrogate mother appear to be very similar…As far as we can observe, the infant monkey’s affection for the real mother is very strong, but no stronger than that of the experimental monkey for the surrogate cloth mother.”

Something was not going well. Something bad was happening. A cloth mother was just as good as a real mother; touch was central to the primate heart, and yet, here it was: Over the following year Harlow noticed the cloth-mothered monkeys were not thriving—this, after he had made such a bold pronouncement in front of all his peers. When he took the cloth-mothered monkeys out to play and mate, they were violently antisocial. The females attacked the males and knew nothing about correct sexual posturing. Some of the cloth-mothered monkeys began to display autistic-like features, rocking and biting themselves, sores blossoming open on their black arms, the blood rising up through the fur like bright pulp. Infections set in. One cloth-mothered monkey chewed off its entire hand. Something, now he saw, something had gone terribly, terribly wrong.

“Of course he was disappointed,” says Harlow’s biographer, Deborah Blum. “He thought he’d isolated the one variable essential to mothering, touch, and that this was a traveling variable, so to speak; anyone could provide it, and he’d made that announcement public, and then, over the next year, he saw his monkeys reacting badly” A New York Times reporter came out to Madison to do a follow-up on the soft mother surrogate and Harlow led him to his lab, where a troop of rocking, head-banging macaques sat in cages, eating off their fingers. “I admit it,” said Harlow. “I have made a mistake.”

Len Rosenblum, one of Harlow’s students at the time and now a renowned monkey researcher in his own right, says, “So we came to understand there were other variables to mothering; it wasn’t just touch, and it wasn’t just face. We hypothesized it had something to do with motion too. We made a surrogate that could rock, and the babies were almost normal then, not completely, but almost. We then tried a rocking surrogate with one half hour a day when the baby could play with a live monkey and that produced an absolutely normal kid. What this means is that there are three variables to love—touch, motion, and play—and if you can supply all of those, you are meeting a primate’s needs.”

Rosenblum goes on to repeat that “the kids” only needed one half hour a day of play with a live monkey. “It’s amazing,” says Rosenblum, “it’s amazing how little our nervous system needs in order to turn out normal.”

In some respects I’m glad to hear this. I interpret these results to mean: it’s incredibly hard to mess up your child. A little jiggle, a soft sweater, and only thirty minutes of actual primate interaction. Any mother can do this: lazy, working, wired, iron—we can do it! Harlow said we can.

Anne Landers began to write about him in her advice-to-mothers column. What would his next experiment be?

William Sears, the famous attachment parenting advocate, a pediatrician who preaches sleeping with your babies, keeping them close at all times, is a Harlow-made man, whether he knows it or not. Orphanages, social service agencies, the birthing industry all had critical policies altered based in part on Harlow’s findings. Thanks in part to Harlow, doctors now know to place a newborn directly on its mother’s belly after birth. Also thanks in part to Harlow, workers in orphanages know it’s not enough to prop a bottle; the foundling must be held, rocked, see, smile. Thanks to Harlow and his colleagues in the study of attachment, we have been humanized—we possess an entire science of touch, and some of this came from cruelty. There’s the paradox.






Opening Skinner’s Box: Great Psychological Experiments of the Twentieth Century
Lauren Slater



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