An eight-month-old baby with rosy cheeks sits in front of a camera. A man appears in the frame and places a live rabbit near the baby. Then the man brings over a small, squirming spider monkey on a leash. Then a dog. The baby, who would become known as Little Albert, seems to have a healthy curiosity about the animals.

But what happens next made the experiment a staple of psychology textbooks and brought it into the pantheon of unethical scientific research.

Dr. John Watson was a psychologist and considered the father of behaviorism. Building off of Pavlov’s work proving that you could “hardwire” certain behaviors into dogs, Watson suspected that the same would apply to humans. In the “nature vs. nurture” debate, Watson was at the extreme end of the nurture spectrum. “Give me a dozen healthy infants,” he wrote, “well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select — doctor, lawyer, artist, merchant-chief and yes, even a beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors.”

Watson was positioning himself as a kind of demi-god, molding or mangling the unformed clay of a human life. And the “specified world” he imagined bringing children into was harsh. He believed that giving them affection was a “mawkish sentimental” act and should be avoided—otherwise the child would develop an “emotional disturbance.”

He decided to test his theory about conditioning by manufacturing a phobia in an infant. More specifically, he would instill a phobia of furry animals in Little Albert.

First, he and his graduate assistant, Rosalie Rayner, had to determine that Little Albert was not already afraid of them. Since Little Albert had watched the animals with interest and in some cases tried to touch them, he clearly wasn’t. Next, Dr. Watson brought the rat back. When Albert reached for it, he heard a disturbing noise: a hammer clanging against a metal bar. Little Albert jerked away from the rat, visibly startled. When Albert tried to reach for the rat again, the researchers made the sound again. Then they sent Albert home for a week. When he came back, they started over again, startling Little Albert as they brought out the animals. As they expected, Little Albert’s fear transferred to other furry objects, even a fur coat. As he saw the animals and heard the clanging sound, he trembled and cried or tried to crawl away.