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Hank: A lot of exciting neuroscience was happening in 19th-century England. Victorian scientists were figuring out that certain parts of our brains are connected with certain parts of our bodies, like different senses or muscles. But mixed in with all the legitimate research was some pseudoscience, or misleading ideas that spread without rigorous scientific backing. Like one theory from the Viennese physician Franz Joseph Gall, who thought that character traits, like religiousness or curiosity, were also linked to specific brain regions.

This theory became the basis of phrenology, a field of study that claimed that you could determine someone’s personality by the shape of their skull. Phrenologists believed that all human brains were made up of many distinct “organs” that could be mapped to personality traits. They claimed the more you used a certain brain region, the bigger it got. And the less you used it, the smaller it got — kind of like how muscles work.

And they assumed that the skull conformed to the shape of the brain, revealing where these bigger and smaller “organs” were. So, theoretically, you could inspect someone’s skull, and use a map of these “organs” to figure out parts of their personality.

Phrenology became enormously popular in the UK around the early 1800s, and spread to places like America, France, and Germany. It was pretty much a load of garbage and guesswork, and many scientists were vocal critics. But at the time, there wasn’t enough evidence to thoroughly debunk the theory.

Researchers would’ve, of course, dissected the brains of dead people, not living people, and the human body changes a lot after death. So even if living brains were different shapes, dead brains probably looked pretty much the same.

Plus, the public thought phrenology was really compelling. Just like horoscopes, people tend to love things that tell them something about themselves. So, phrenology thrived on subjective validation, which is the idea that people tend to believe in something if it’s personally true or meaningful for them. But as the ideas spread, they started being used to justify race and class inequalities.

Upper classes used phrenology to reassure themselves that they were supposed to be on top, because of the ideal shapes of their brains. Lower classes, on the other hand, accepted the pseudoscience because it claimed that these brain “organs” could be developed, so they could improve themselves with hard work. The American physician Samuel Morton made even more sweeping claims about skull shape in his book, Crania Americana.

Morton argued that Caucasians were superior to other races, like Africans and Native Americans, because of craniometry, or different skull and supposedly brain sizes. Which is just racism under the guise of science. Some phrenologists used these ideas to rationalize slavery and colonization, while others were anti-slavery because they thought these “inferior” races ought to be protected.

Eventually, all this "scientific" racism was acknowledged, and phrenology’s legitimacy took a nosedive in the mid-1800s as we continued to learn more about how the human brain actually works.

First of all, the brain conforms to the shape of the skull, not the other way around. And secondly, the brain doesn’t physically grow or shrink like our muscles. Phrenologists were also wrong that the brain was made up of discrete chunks — it’s one organ with a bunch of networked cells.

But there was something to the idea that the brain was spatially organized, and different regions were linked with different functions — which we call functional specialization. The French physician Paul Broca contributed some evidence to support this idea in the 1860s.

He found that damage to the left frontal lobe in humans was linked to speech impairment, without affecting someone’s ability to understand what other people were saying. In the 1870s, Gustav Fritsch and J.L. Hitzig were experimenting with stimulating different parts of the cerebral cortex of a dog, which produced movement in different areas of its body.

Through experiments like these, scientists were able to develop a better understanding of different regions of the brain by the start of the 20th century. Unlike phrenological maps, which assigned arbitrary brain areas to personality traits, our current brain maps are based on experiments that show different functions of each region. With the development of technologies like Magnetic Resonance Imaging and Computed Tomography, and the ability to do careful brain surgery, our understanding of neuroscience continues to grow.

Nowadays, we’re positive that phrenology was junk science. The shape of someone’s head doesn’t say anything about their personality, character, or moral depth. But we can still see its echoes in language we use today, like “highbrow,” “lowbrow,” and “well-rounded.” Phrenology may have lacked scientific merit, and was definitely used to justify harmful ideas, but it did cause scientists to think more critically about how biology is intertwined with thoughts and emotions.

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