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The skulls of ancient pearl divers come with abnormal ear canal bone growths [arstechnica.com]

Surfers, divers, and others who spend time in cold water sometimes suffer from a condition called "surfer’s ear [wikipedia.org]," in which a small bony bump forms in the temporal bone, blocking part of the ear canal. Archaeologists recently found the same bony growths in the skulls of people who lived in pre-Columbian Panama up to 2,400 years ago. They suspect the skulls are the remains of expert pearl divers who spent their lives freediving for valuable items on the ocean floor.

The skulls were part of a large collection examined by archaeologists Nicole Smith-Guzman and Richard Cooke of the Smithsonian Tropical Research Institute. They found the telltale bumps on the temporal bones of eight skulls with intact ear canals—seven men and one woman. Among the skulls that still had intact ear canals on both sides, 12.2 percent of the men and 3.3 percent of the women had surfer’s ear on at least one side. Most had mild or moderate cases, but one man had enough growth to block more than two-thirds of his ear canal, which may have been enough to cause noticeable hearing loss.

The relatively low frequency of the growths suggests a select group of mostly men who, for some reason, regularly ended up with cold water in their ear canals.

Panama is a tropical spot, but the water in Gulf of Panama, on the country’s central Pacific coast, can get pretty chilly. That's because from January to April trade winds from the north blow most of the warm surface water out to sea, and colder water wells up from the depths to replace it. At an average surface temperature of 19C (66.2F), the Gulf is cold enough to present a risk of surfer’s ear.

Most people living along its shores, especially men, probably spent a lot of time on the water, because fishing from boats was an important part of the local economy. If the cool salty spray and brisk ocean wind were enough to cause surfer’s ear, you’d expect more than one man in ten from pre-Columbian villages along the Gulf to develop the problem. The relative rarity of the condition suggests that a small number of people on the Panamanian coast were doing something more immersive—and diving for oysters fits the bill.

The divers would have played an important role in Panama’s pre-Columbian economy. Jewelry made from conch shells, silvery mother-of-pearl, and orange and purple thorny oysters traveled along trade routes as far north as Mexico and as far south as the Andes. Archaeologists have found shell jewelry in graves dating back to 400 BCE. The organisms that made the largest and most prized of these shells would have anchored themselves to the rocky seafloor in clear water, deep enough that only skilled free divers could reach them. Spanish conquistador Vasco Nuñez de Balboa described expert divers swimming 7.9 meters (24 feet) down to pry oysters from the rocks.

Those divers, according to Balboa, began their training as infants. All of the individuals in Smith-Guzman and Cooke’s study with surfer’s ear lived to be at least 35, so they would have spent decades diving down into the cold water of the Gulf of Panama to bring up valuables. That long-term exposure could explain the cases of surfer’s ear, which takes several years to develop.

Doctors think surfer’s ear happens because the thin skin of the ear canal doesn’t protect the bone from cold water, which causes inflammation in the membrane on the outside of the bone, called the periosteum. Over time, that inflammation turns causes the bone to lay down extra layers, similar to the way bone spurs form. That increases the risk of infection, because it’s harder to clear water and debris out of the ear. A severe enough case—one that blocks more than about two-thirds of the ear canal—can cause hearing loss.

Elsewhere in coastal Panama, the water stays warmer year-round. No signs of surfer’s ear turned up in remains from sites along those coasts, even though people there almost certainly also dived for oysters and conch. But Smith-Guzman and Cooke could only examine five skulls from sites along the Caribbean coast and the Gulf of Chiriqui, so they don’t have enough information yet to say for sure that pearl divers in those places definitely didn’t suffer from surfer’s ear. They’re hoping to change that with future studies.

“We want to do a follow-up study in which we look at skulls from a much wider area and also a survey of doctors in Panama to find out if surfers or divers ever show up with surfer’s ear these days,” said Smith-Guzman in a statement.

American Journal of Physical Anthropology, 2018. DOI: 10.1002/ajpa.23757;( [doi.org]About DOIs [arstechnica.com]). [doi.org]

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