Last December, pediatric dentist Kevin Boyd hunched over a tray of plaster casts of children’s teeth in a basement laboratory at the Penn Museum in Philadelphia. He pulled down the glasses perched on his head to peer at the tiny molds spread across the black-topped tables. He measured the distance from molar to molar, jotted down a figure, and turned to the next tray.

Yellowed skulls in glass cases lined the room. Janet Monge, who is responsible for the physical anthropology section of the museum and its collection of skeletons, perched on a stool nearby.

Janet Monge, the Keeper of Collections, Physical Anthropology Section at the Penn Museum. Photo by Jonah Rosenberg

“What happened?” Boyd asked me and Monge, turning a mold over in his hands. “How could all of a sudden we develop crooked teeth and narrow jaws, and impacted nasal airways? That’s only recently happened, and it coincides with women going into the textile mills in the industrial revolution.”

We often think of evolution as something that happened in the distant past, transforming Cro-Magnon people into our modern selves. The “evolution of humankind” timelines in natural history museums typically span hundreds of thousands of years and end with the earliest evidence of written language, a few thousand years B.C. But the truth is that our bodies are still evolving — our brains are shrinking, our elbows are narrowing. And our faces are still changing too, leading to dramatic changes in our teeth, noses, and jaws.

Slides courtesy of Kevin Boyd

Skeletal records show that for hundreds of thousands of years, people had beautiful skulls: straight teeth, wide jaws, forward faces, large airways. Robert Corruccini, an emeritus anthropology professor at Southern Illinois University, found perfectly straight teeth and wide jaws in children’s skulls from pre-Roman times among Etruscan remains in southern Italy.

Then, about 250 years ago, our faces began to change. Boyd argues that industrialization interrupted the ancestral patterns of weaning and feeding, with babies nursing on demand for years while also trying solid foods under adults’ watchful eyes. Boyd says that the widespread adoption of bottle feeding, pacifiers and soft processed food deprived toddlers of practice chewing and distorted the shapes of their mouths. (“In modern society you have Gerber’s baby food,” Corruccini told me. “Etruscan kids had to chew once they were getting off breast milk. Babies have remarkably powerful chewing capabilities.”) Just like diabetes and heart disease, malocclusion — the misalignment of jaws and teeth — followed industrialization around the globe. Meanwhile, people in societies that never industrialized enjoyed well-aligned teeth and jaws.

Other factors may have played a part too. Environmental pollutants and recirculated indoor air increased the strain on our bodies and worsened pregnant women’s health in regions that industrialized first. That can impact skull shape of babies in utero by affecting birth weight, jaw length, and size of sucking pads in the cheeks. Skeletal records of animals show similar differences in skull shape between animals raised in the wild and those raised in captivity — suggesting that humans’ modern diet and environment play an outsized role in our evolving faces.

One of the first to recognize the shrinking skull was Charles Darwin, who described “civilised” humans as having shorter jaws than the “savages” who lived in non-industrialized societies, in The Descent of Man. “This shortening may, I presume, be attributed to civilised men habitually feeding on soft, cooked food, and thus using their jaws less,” he wrote. “I am informed by Mr. Brace (the U.S. philanthropist Charles Loring Brace) that it is becoming quite a common practice in the United States to remove some of the molar teeth of children, as the jaw does not grow large enough for the perfect development of the normal number.”

In the 1920s and ’30s, a dentist named Weston Price traveled around the world, taking photographs of the teeth of indigenous people in Africa, Europe, North and South America, and Australia. His photos confirmed Darwin’s suspicions — he documented well-aligned teeth, high palates and forward jaws of non-industrialized populations. Price and Darwin may have been motivated by abhorrent beliefs — eugenics-informed ideas about “civilized” (Caucasian) races being an improvement on “savage” races (African and indigenous peoples) — but their research can still prove useful to modern researchers tracing the evolution of human skeletons.

Perfect occlusion of the teeth was the norm up to about 250 years ago. Photo by Jonah Rosenberg

Early 20th century orthodontists recognized that short jaws and high, narrow palates posed a threat to breathing, Boyd said, plopping his black Patagonia backpack on the lab table. He pulled out a stack of papers from 1917 and 1922, including the precursor to the New England Journal of Medicine. The journals advise dentists to correct any irregular teeth or facial structures before the child turns six, with the authors stressing the importance of nasal breathing and wide dental arches. Other papers at the time recommend interventions as early as 30 months of age and include pictures of palate expanders from the 19th century.

Yet some time around the 1940s, this understanding of how our shrinking jaws endangered breathing seemed to disappear. Boyd and like-minded researchers hope to extract the knowledge embedded in the museum’s skulls and bones and use it to better document how our skulls have evolved. They’ve already taken a collection of cone-beam computed tomography images — 3D CT scans — of children’s skulls from ancient and modern times, some from the nearby practice of orthodontist Marianna Evans. They hope to collect many more, visualizing airway volume and structural blockages.

“I have a CBCT of a five-year-old caucasian who died 250 years ago, and a five year old who’s in my office referred from a pulmonary physician because the kid has sleep apnea. And I can show how that jaw compares to one who died 300 years ago, and how much smaller it is,” Boyd explained to me, as we packed up to leave the museum for the day. Monge watched intently to be sure he replaced the dental molds in the correct trays.