A new version of Samuel Morton's collection of skulls in the 19th century

The scientists produced almost equivalent results, but what they deduced differed radically: Tiedemann used his own to fight for equality and the abolition of slavery and against the 39 idea that different races are created separately. Morton's research was used to maintain the status quo in the United States, which meant, at that time, racial division, hierarchy, and slavery.

Although this work took place almost 180 years ago, it still raises debates, particularly on the concept of scientific racism and prejudice. An article published in PLOS Biology Paul Wolff Mitchell, Ph.D. candidate at the University of Pennsylvania, adds to the conversation by analyzing handwritten and never-analyzed cranial measurements he discovered in Morton's archives.

Mitchell determined that, even though Morton's data collection methods produced accurate numbers and were probably not intentionally biased, the scientist's findings – that Caucasians had the largest skull size and therefore , the highest intelligence, and that Africans had the smallest skull size and the weakest intelligence – were obviously. They also emphasize the importance of scientific interpretation.

"Both Morton and Tiedemann thought that the bigger and more complex the brain, the higher the individual or species," says Mitchell. At the time, many scientists were convinced that modern science had refuted. "Beyond that, more than the data has informed their scientific positions," he adds. "Political and ethical considerations were too."

"It's a complex story," says Mitchell, which requires going through Morton's process and what followed to grasp its complexity.

Morton Science Trail

Morton, a physicist and naturalist from Philadelphia, recognized as the first physical anthropologist, began collecting human skulls in the early 19th century. Although he did not travel much himself, his role as President of the Academy of Natural Sciences allowed him to correspond with scientists from around the world to obtain samples.

He wanted to bring together a sufficient number of people belonging to each of the five recognized racial groups: Ethiopian (or African), Amerindian, Caucasian, Malay and Mongolian. In total, he amassed about 900 skulls, the largest academic collection of the time, and the same for half a century after his death. Today, the Morton Collection is preserved and preserved in the Physical Anthropology section of the Penn Museum.

As a first step, Morton measured the size of 256 skulls by pouring white pepper seeds into each cavity, then measuring in cubic inches the volume of seeds needed to fill a sample. From this work, he published Crania America in 1839, which reported statistics on each Native American skull and averages for other groups. The following year, he published the first of three catalogs of skulls, then a book entitled Crania Aegpytiaca. The second catalog appears in 1844.

In trying to replicate his seed measurements, Morton had difficulty, so he switched to lead shot and redid the measurement process, now with 672 skulls. "He came to the same conclusion as before," says Mitchell, "Caucasians with the largest brain size and the smallest Africans". In 1849, Morton published a third and final catalog with cranial data based on the lead measurements of each skull.

He died just two years later, then considered a leading expert in his field. Until Charles Darwin published On The Origin Of Species And The United States Fought Civil War.

See something new

For more than a century after these two events, Morton 's science has fallen into the shadows, his methods have been modernized and outmoded, his theories have been debunked. Then, in 1978, American scientist Stephen Jay Gould wrote several texts on scientific racism, on the idea that scientific discoveries could justify persistent discrimination and intolerance. He used Morton's skull studies as a typical example.

"Gould notices that the average for Africans between seed measurements and shot measurements is increasing a lot, but that the average for Caucasians' measurements is increasing only a little, about as much as the measurements for Native Americans," says Mitchell . . "This leads Gould to conclude that Morton unconsciously underestimated the size of Africans' brains."

Due to the compressible nature of the seeds, Gould suggested that the skulls could be overloaded inadvertently or slightly packaged, which would produce inaccurate numbers. Gould speculated that Morton had unconsciously done so, bundling seeds into Caucasian skulls and filling only the African skulls slightly, leading to a systematic underestimation of African cranial capacity.

Unbeknownst to Gould, however, he did not have all the facts, namely complete seed data that Morton never published – data that Mitchell rediscovered in the scientist's records at the Academy of Natural Sciences.

"I was browsing Morton's old skull catalog, which he had printed three times throughout his life to let other scientists and collectors know what he had in his collection," he said. says Mitchell. "He also kept personal copies, which he signed and dated." The first copy dates from 1840. "

This first edition did not include the size of the printed brain as the last two, but in Morton's personal copy, Mitchell noticed handwritten measurements accompanying many entries, some scraped and rewritten. He also found that the brain measurements from the 1840 and 1849 catalogs differed, leading him to conclude that the recorded measurements corresponded to seed measurements never seen before.

Having worked with Morton's skulls since 2010, under the tutelage of Janet Monge, curator of the Penn Museum's physical anthropology section and assistant professor of anthropology at Penn, Mitchell had an intimate relationship with the collection. . "I know these skulls well," he says. "When I looked at what Morton had written, I said," There is something wrong here. This is not the extent that he gives later. "It's thanks to a great familiarity with the skulls that I've been able to see something new in these documents."

What does all this mean?

For Mitchell, consulting the entries for the original seed measures rather than averages for four of Morton's five racial classifications alters the conversation about these skulls. Mitchell's analysis confirmed that Morton's measurements were accurate. the averages of measurement of the seeds and stems differed because of the different size of the sample.

But, he notes, this discovery is almost immaterial.

"The fact that Morton's data are not skewed does not mean that his science was not," Mitchell said. "He can measure skulls very accurately but also be a biased scientist." Just look at Tiedemann, he says. "The German scientist basically does the same thing as Morton but ends in a radically different conclusion."

Through his work, Tiedemann has noticed a range of skull sizes in all humans. Morton, on the other hand, has focused on the average brain size of different breeds. Although the Morton figures overlap from one breed to another and that, if we take the averages of the Tiedemann data – which he has never done himself – reveal an almost perfect correspondence with that of Morton, the differences of interpretation of the two scientists confirm their divergent conclusions.

In regards to current science, Morton's biggest fault may lie in the fact that he has not collected data on body size, Mitchell says. The size of the brain is correlated with body size, and the size of the brain and body is a well-known adaptation of the climate in which people live. This means that, from the point of view of evolution, there is no reason to suppose a link between the size of the skull and the intelligence.

"If you only collect heads around the world and you do not consider the size of your body, there is no effective way to compare your data," Mitchell said. "People with bigger bodies have bigger brains."

The other problem with Morton's research, he notes, is that the racial categories he assumes have no biological basis. All this leads Mitchell to wonder what, ultimately, Morton's data can really teach.

"When it comes to moral and political issues, interpretation is a key part of how science is done," concludes Mitchell. "This will always include an element of bias, the only way around the problem is to have an open data presentation, a thorough review of the scientific work and a diverse community of people working on these issues and reflecting on them. "

Explore further:
Samuel Morton collection of skulls at the center of the controversy

More information:
PLOS Biology (2018). DOI: 10.1371 / journal.pbio.2007008