In the late 1950s, a middle-aged primate researcher named Harry F. Harlow set himself a challenge: he would build a perfect mother for the baby monkeys in his laboratory. There were, of course, some practical challenges to perfection. The mothers had to stand up to the tendency of little monkeys to chew, unscrew, and take apart all objects in their cages. Harlow and his psychology students first tried making the heads made out of inexpensive pine balls. The small animals gnawed those into pulp.   

“Professor Harlow,” one of the students told him worriedly. “The baby monkeys are destroying the mothers.” Harlow, typically, was amused. He lit another in his ceaseless chain of cigarettes and deadpanned his answer: “Children have been destroying their parents for years.”

The scientists switched to hard maple billiard balls for the heads. They used bicycle reflectors for the eyes. Hard plastic for the curved mouth and jug-handle ears. In photographs, Harlow’s lab-designed perfect mother has a face that seems half-clown, half-insect. But then, as he would later point out, “a face that will stop a clock won’t stop a baby.” It wasn’t the head, or the bug-eyed face, that was the point of the experiment anyway. It was the body that mattered.

The body of the ideal mother, Harlow believed, would be as soft as a cushion, warm as sunlight. Under his direction, at the University of Wisconsin in Madison, the “cloth mother” would have a cylindrical terry cloth body padded with fluffy filling and warmed by a light bulb. He was positive, even before the study was finished, that she would prove to the world that babies need a soft touch. An irrepressible writer of verse, he serenaded the cloth mother in a 1958 speech to his fellow psychologists: Though mother may 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.

It’s almost hard to believe now, in the 21st century, when we so readily hold and comfort children, that Harlow had to fight so hard in praise of a simple hug. That he did reveals not just the man, but also the scientific community with its stubborn insistence that children should be toughened up rather than nurtured. Psychologists of the time wouldn’t even use the word love. They described a child’s relationship to its parents as “proximity.” In a memorable loss of temper, Harlow once snapped at a visitor in his lab, “Perhaps all you’ve known is proximity. I think God that I’ve known more.”

It was his willingness to fight, in addition to those carefully designed mother-and-child experiments that helped bring about one of the most important and underrated revolutions in 20th century psychology. In the end, the experiments would make their creator not only famous but infamous. Harlow recognized that love is not always kind. Parents do not always love their children either. His later explorations of rejection, abuse, social isolation are still painful to read. In one notably grim study of “evil” mothers, he equipped a cloth mother with brass spikes that would jam against a clinging baby. To critics – and there were many - he pointed out that such mothers exist in nature. “If you’re going to study love,” he replied, “you have to study love in all its aspects.”

Harlow died in 1981 but he remains one of the most influential primate researchers in the history of science. He intentionally helped rewrite the rulebooks of child psychology in the best possible way. He unintentionally helped rewrite the ethics code for animal research, sometimes in the worst possible way, by doing experiments so troubling that even his fellow scientists were haunted.

On either count, he seems an unlikely revolutionary. Born in 1905, he grew up in a small Iowa farm town. His father, Lon Israel, was a half-hearted businessman, preferring to tinker with inventions in their garage. Harry grew up poor, shy and not a little insecure. He was a slight boy, a little stoop-shouldered, dark-haired and dark-eyed, who liked to dream big. His saving grace was a natural sense of mockery. He was always ready to laugh at himself, even at his awkward teenage years: “I tended to apologize to doors before opening them.”

With the help of relatives, his parents found money to send him to Stanford University in California. There he both gained a PhD in psychology in 1930 and a different last name. His professors worried that, due the extreme anti-Semitism of the time, the surname of Israel could harm his career. Still dreaming of a great future, he took his father’s middle name instead and became Harry Harlow.

But as an Israel or a Harlow, he would ever be driven by that childhood need to prove himself. “Insecure?” says his former graduate student, Stephen Suomi, now head of primate behavioral programs at the National Institutes of Health. “Always.” He spent most of his career at the University of Wisconsin in Madison. There he became fascinated with the small colony of monkeys and apes at the city zoo. He watched a pair of orangutans argue and make peace. He watched a temperamental baboon patiently struggle with a test in order to please a favorite trainer. “These are not just monkey stories,” Harlow said. “They are human interest stories.”

He persuaded the university to let him remodel an old factory into a primate laboratory. In the mid-1930s, he began a series of experiments designed to test for primate intelligence. He designed an apparatus that used object-packed trays to challenge monkeys’ abilities to remember patterns or solve puzzles. He became absorbed in the challenge himself. He wanted to prove that these were smart animals, they could learn, get smarter. The quest – and he definitely saw it that way - took over his life.

Harlow’s first wife, Clara, left him, taking their two young sons. He had basically abandoned them anyway, she said. He then married a colleague, child psychologist Peggy Kuenne. They also had two children, but he spent little time in that home either. Harry Harlow woke up and went to sleep with the call of laboratory sounding in his ears.

He continued to arrive at his little primate facility as the sun crept upwards; he continued to leave in the dark. He went there seven days a week, fueling his obsession with cigarettes, coffee, and alcohol. There were nights, more than anyone could count, that Harlow’s graduate students drove him home from the corner bar. And just as many days when he stood up drunk to give a speech, and made it with startling passion and precision.

He was pushing himself hard. But he was still focused, still absorbed in the laboratory life. His observations of monkeys had led him to realize their intelligence. And he was beginning to realize something else. He’d been trying to set up a nursery for baby monkeys, a place where they could be sheltered from infections. In their clean cages, the infant monkeys tended to cling to the soft towels that lined their cages. They rocked in them, wrapped themselves into the cottony folks. The little animals reminded him, intensely, of human babies and their own tendency to cuddle into a blanket or pillow when separated from their mothers. And he Harlow began to wonder: were the monkeys trying to tell him something? He began to consider the relationship of mother and child, the beautiful security of being held and of holding on in return. Perhaps, there was something absolutely essential, in what Harlow called “contact comfort.” Perhaps, he suggested, in those early days, touch is our most effective way to convey love.

In retrospect, the “perfect mother” had a remarkably defiant aspect to her. Mainstream psychology had been arguing for decades that affection was unnecessary in parenting and that parents who held and cuddled their kids might even be doing them harm. “There are serious rocks ahead for the overkissed child,” warned behavioral psychologist John Watson in his 1928 best-selling childcare book.

Under the prevailing “conditioned response” model, nurturing parents trained their children to be clingy and weak. The theory discounted positive emotions. Children didn’t feel love for their parents. They were conditioned to respond, primarily because their parents fed them. It was as simple as one of B.F. Skinner’s pigeons pecking at a lever in order to get corn.

It was that idea– the simple, conditioned child – that Harlow chose to challenge.

Not only did he and his students build the cuddly cloth mother but they built a “wire mother” with a cylindrical wire body and an equally repulsive face. In one early experiment, they put cloth and wire mothers side by side in a cage. Only wire mom had a milk-filled bottle. Cloth mother was nothing more than a soft touch. The scientists then let baby monkeys into the cage and watched them.

The results dismantled any notion that the mother-child relationship was built on feeding. The little monkeys lived on cloth mom. Some of them refused to let her go even when hungry. They clung to her while reaching over to suck milk from the nearby wire mother’s bottle. This was about love, Harlow said firmly, not about training. All of us, he said, need to grow up with a solid foundation of affection; touch is simply one of the ways we build that base.

If he had stayed there, in the gentle science of touch, would he have stayed a hero? He had a moment of heroics, at least. British psychiatrist John Bowlby credited Harlow with helping to rescue attachment theory, to convince everyone that parent-child relationships mattered. Harlow was a media darling, a widely sought expert on childcare, the first (and only) primatologist to receive the White House Medal of Science.

But, of course, he was too restless not to move on. He believed in love, all right, but he didn’t think it was simple. He had realized – not surprisingly in retrospect - that cloth mother wasn’t perfect at all. Why? She didn’t interact, she didn’t teach. She was a huggable dummy with, as Harlow said, “a social IQ of zero,”

He began to explore “mother intelligence.” He wondered what parents teach their children, for better and for worse. Good mothers teach their children to be good friends to others, he found. Cloth mothers, obviously, failed in that entirely. And his evil, rejecting mothers were even worse. He found that no matter how the evil mothers slapped them away, the baby monkeys always returned. They coaxed and stroked and tried to get their mothers to love them back. They would give up friendships in their efforts to engage their parent.

Harlow became fascinated with whole social network. He explored the idea that one relationship can heal emotional damage caused by another. He found that “peer therapy”, time with other friendly youngsters, could help little monkeys raised by rejecting mothers and even dummy mothers. He found that good mothers know when to keep a child close and when to urge it away into the company of others.

The real vulnerability was dependence on one relationship, he thought. He was just beginning to explore the effects of isolation when, in 1967, his second wife, Peggy, was diagnosed with terminal breast cancer. In the years of her illness, Harlow tumbled into a severe depression. He became convinced that depression itself was a social isolation, an empty emotional wasteland. He began to devise more extreme experiments - complete isolations, some as long as a year.

It was in this period that Harlow created his “pits of despair.” They were V-shaped chambers, built to trap a monkey in the dark point at the bottom of the structure. They were dismayingly effective. Within a few hours, the monkeys would curl into apathetic huddles. “I said. ‘Why are we doing this?’” recalls Wisconsin psychologist Charles Snowdon. “ And he said, “Because this is what depression feels like.”

For Harlow, the depression experiments were a necessary dive, a plunge into social vulnerability. But for others, they were too deep and far too dark. “An isolate monkey will break your heart,” says Steve Suomi, flatly. When Harlow retired from the University of Wisconsin in 1973, a year after Peggy’s death, and retired to Arizona, his former colleagues ripped out the isolation chambers and threw them away.

Harlow never expressed regrets for his monkey experiments although he always acknowledged the animals suffered. “Remember for every mistreated monkey, there are a million mistreated children,” he once told a newspaper reporter. “If my work will point this out, and save only one million human children, I can’t get overly concerned about ten monkeys.” His real worry was whether he’d made his point. In his last years, hobbled by Parkinson’s disease, he wrote to a friend that he wished he had been able to more dramatically change people’s ideas of love. “Perhaps though,” Harlow wrote, “one should always be modest when talking about love.”