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Dr. Harry Harlow's rhesus monkey experiments in the 1950s contributed a great deal to psychologists' understanding of attachment theory. Unfortunately, his later experiments also contributed a great deal to the need for ethics regulations.

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A lot's changed in the last 60 years or so when it comes to how psychologists think about parenting, especially when it comes to the relationship between a child and their caregivers.

In the 1950s researchers were still trying to figure out whether children bonded with their caregivers only because they were the source of food when they were babies, or, if there is more to it than that, and some of the answers were drawn from the research of an American psychologist named Harry Harlow. But Harlow's kind of a controversial figure in psychology.

Today many psychologists think that his methods were inherently unethical, because of the way he treated the rhesus macaque monkeys he used as subjects, and nearly everyone agrees he took things too far. [Intro]. When he first started out doing monkey research in the 1950s, Harlow was mostly interested in how they learn. He'd isolate rhesus macaque monkeys from a young age and use them in his studies.

As he did this research he noticed that the young macaques seemed to *really like* the cloth blankets that covered the floors of their cages. They spent a lot of time with them clutching them like security blankets, and if he took one away, they'd freak out. This might not seem too surprising, but at the time there was a bit of a debate in psychology about this sort of thing.

On one side there were the behaviourists who thought that the only reason infants grew attached to their mothers was because their mothers gave them food, like breast milk. A stimulus-response sort of thing. On the other side was a psychologist named John Bowlby who thought there was, well, more to it than that.

Among other things, he argued that a parent was a source of security and comfort. Harlow thought the monkeys might be getting this sense of comfort from the blankets, and he designed an experiment to test it using two inanimate objects that would act as surrogate mothers, one made of wire and wood, and another made of soft cloth. First, he wanted to see how much time the monkeys would spend with each surrogate if only the wire surrogate supplied food.

The monkeys' preferences were clear - they go to the wire mother for food, but then spend the rest of their time cuddling with the cloth mother. To be extra sure he varied which one was the source of the food, and then scared the infant monkeys with a motorized toy to see which mother they ran to. But it didn't matter where the food was, the monkeys clearly preferred the comfort and security of the cloth mother.

Harlow proposed that the cloth mother provided contact comfort for the infant monkeys. It was solid evidence against the behaviorists. His research supported the idea that the monkeys had emotional and attachment needs for their mothers.

So you'd think maybe his next move would be to *stop* doing studies that involved raising infant monkeys in isolation, right? Unfortunately, no. His next move was to do studies that extended the isolation.

He isolated monkeys using a kind of vertical chamber for up to a year after they were born, and then introduced them to other monkeys to see how they'd interact. No surrogate. No other monkeys.

Just an inverted pyramid monkeys couldn't climb out of. His nickname for it was the "pit of despair". And that was awful.

When monkeys were released, they didn't move much, didn't explore their environment, and kept rocking and clasping themselves. Some avoided others entirely, and a few got really aggressive. And it's not like these were just unfortunate side effects of his research; these are the variables he was *interested* in.

He wanted to explore the relationship between social isolation and mental illness, so he was trying to use social isolation to induce psychopathology and depression in monkeys. There are only so many ways you can measure the sadness of a monkey, but they showed clear signs of depression and trauma. He also found that the female monkeys weren't that interested in sex, but if they were impregnated anyway, they didn't care for their babies.

Missing that care taking experience as an infant seemed to make them incapable of it as adults. Harlow continued doing these kinds of experiments for years; some of them, especially the earlier ones, did help shape psychologists' understanding of the bond between children and their caregivers, and how that bond affects a child's mental health. But this kind of research wouldn't be considered ethical today.

The experiments would have to be approved by a review board, and though they always need to weigh the benefits versus potential harms, this kind of research would be considered an unjustifiable amount of pain and distress with little scientific gain. There might have been some scientific value early on, but even if you give Harlow the benefit of the doubt when it comes to his first studies, he didn't seem to learn the lessons of his own research – that these monkeys had emotional needs. Thanks for watching this episode of SciShow Psych, which is brought to you by our patrons on Patreon.

If you want to help support this show, you can go to, and don't forget to go to and subscribe. [Outro].