Ear Bones Suggest Prehistoric Aquatics

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March 23, 2007 — Determining the daily activities of prehistoric people is difficult without written records, but scientists have figured out a way to identify individuals who often engaged in intense water-related activities, such as diving, surfing and fishing.

The clue is in their ears.

According to a paper accepted for publication in the American Journal of Physical Anthropology, abnormal ear canal bone masses, called auditory exostoses, can be linked to aquatic activities. Like a sort of skeletal tattoo, the masses mark the remains of some early individuals.

"Auditory exostoses can develop when the ear is exposed to cold water (below around 66.2 degrees Fahrenheit) and/or to warmer water chilled by the action of cold atmospheric temperature and/or strong winds," explained Sabine Eggers, who worked on the study with Célia Boyadjian and Maria Okumura.

Eggers, a researcher in the Biological Anthropology Laboratory in the Department of Genetics and Evolutionary Biology at the University of Säo Paulo, Brazil, said that the "external region of the ear canal responds to chill with increased blood flow and inflammation."

Bone tissue then produces new cells and, over time, this can lead to bony outgrowths that may be helpful for scientific study, but can cause hearing loss in the subject.

The researchers analyzed 676 skeletons dating from 5,000 years ago to more recent times from 27 coastal and inland native Brazilian groups. As predicted, few inlanders possessed the bone masses, but many coastal groups had them. Skeletons from only one region, the southern part of the state of Santa Catarina, presented differences between the sexes, suggesting that women usually, but not always, went out on the water as men did.

Other clues hint at what the coastal dwellers did above and under water.

"They certainly fished habitually, since fish was their main source of protein," said Boyadjian. "We know that from the fish remains scattered throughout the sites, and the chemical analysis (stable isotopes) from the human bones."

Mollusk shells from shellfish that they could only obtain by diving indicate they frequently swam underwater, while hooks and weights suggest they fished from shore and boats too.

They probably surfed as well.

"One could imagine that kids would use any piece of wood they found to play in the waves, just as kids and adults do today with their boards," Okumura said.

The study confirms earlier speculation about exostoses, which have been identified in ancient skeletal remains from Yugoslavia, the Canary Islands, Middle Europe, other parts of South America and even Imperial Rome.

Paleoanthropologist Georgio Manzi of La Sapienza University in Rome and colleagues studied the Roman skeletons, which dated from the first to the third centuries. The scientists established "close links between the occurrence of auditory exostoses and prolonged cold water exposure, generally due to the practice of aquatic sports, or to working activities involving water contact or diving."

In many of the Roman cases, it appeared that frequent thermal bathing led to the ear canal bone masses, since men would often warm up in saunas and hot baths before plunging in icy pools. Roman women, who usually skipped the freezing cold water routine, had far fewer exostoses.

Eggers thinks Eskimos warded off the problem because they often wore hoods, a fact that should be taken note of today by water sports fanatics.

She said, "Although the use of a hood or earplugs has not been proven to completely prevent the development of auditory exostoses, wearing this equipment can help individuals who have intense contact with water to avoid the development of this anomaly."