Genetic Mutation Behind Shoveled Teeth May Have Been Key to Ancestral Survival

4_24_Shoveled Teeth
Human incisors with significant "shoveling" are pictured. Christy G Turner II/G Richard Scott

The average adult human has 32 teeth—tiny chunks of smooth enamel, bloody pulp, yellow dentin and solid cementum. Beyond chomping, cutting and chatting, these pearly whites can reveal incredible secrets about our past.

Just this year, teeth have helped scientists trace the path of early human migration, proved the continued existence of an indigenous people long believed extinct and even revealed the ancient roots of friendships between humans and dogs. Now, scientists think ancient shovel-shaped teeth might hold the key to the success of Native American ancestors on their journey from Siberia to Alaska. The research was published Monday in Proceedings of the National Academy of Sciences.

The genetic mutation behind shovel-shaped teeth (pictured above) might have helped babies survive the intrepid journey from Siberia to Alaska 20,000 years ago. Sapped of sunlight during winter, ancient humans could have faced serious health conditions. Scientists think the mutation could have also helped women deliver key nutrients needed to stave off health problems in their babies.

Researchers led by Leslea Hlusko, an associate professor at University of California, Berkeley, analyzed data from the ancient teeth of more than 5,000 people from Europe, Asia, North and South America. The researchers discovered almost all Native Americans had shoveled incisors prior to the arrival of Europeans.

Today, nearly 40 percent of Asian people share this dental trait. The genetic mutation behind tooth shoveling—found in two alleles of the EDAR gene—occurred in China some 30,000 years ago and spread through the ancestors of Native Americans and Asians 20,000 years ago. The researchers questioned why these teeth were so common in Native Americans and Asians but rare in other groups.

Sweat glands, hair shaft thickness and branching ducts in the mammary glands—which produce milk in breasts—are all linked to the same genetic mutation, Hlusko noted.

Selection in favor of sweating seemed unlikely in humans spread across Asia and Beringia 20,000 years ago during the last ice age, Hlusko thought. When she considered the pressures actually facing people in northern latitudes, a lack of sunlight jumped out. Humans produce vitamin D when exposed to sunlight—a substance crucial for immune health, fat regulation and calcium absorption. Although children and adults can compensate for a lack of vitamin D by eating animal fat and other foods, babies rely on their mother's milk for sustenance.

Hlusko and team think that mammary branching associated with EDAR mutations might help mothers deliver key nutrients to their babies, making breastfeeding a likely key to the spread of the gene. "This highlights the importance of the mother-infant relationship and how essential it has been for human survival," she said.

Biological anthropologist Julienne Rutherford of the University of Illinois in Chicago found the concept exciting. "Teeth telling us something about fertility? That's really amazing," the scientist, who was not involved with the research, told Science.

Scientists had previously suggested shoveled incisors might be the result of evolutionary selection for use in softening animal hides. Hlusko, however, was unconvinced.

"Why would there be such strong selection on the shape of your incisors?" Hlusko explained in a statement. "When you have shared genetic effects across the body, selection for one trait will result in everything else going along for the ride."

This story spreads far beyond the ancestors of today's Native Americans, Hlusko told Science. "Everyone with shovel-shaped incisors has this gene that may compensate for vitamin D deficiency."