But Lambert’s legacy was more than genetic. He came to the U.S. speaking what historians presume was a regional sign language from his home in Kent; over the years, it evolved and spread into what would become Martha’s Vineyard Sign Language. And while one in 25 people were deaf, something closer to 25 in 25 knew how to sign. Long before the development of American Sign Language, they used sign as naturally as spoken English, and in every combination: Between deaf people, between deaf and hearing, and even from one hearing person to another. The language didn’t belong to the deaf community; it belonged to the town.

“People tended to think of the deaf folks in Chilmark as individuals first,” Van Riper said, “and not about their disabilities, except in a peripheral way. No different than someone who’s very tall or only has one eye.”

Mainland scientists who heard of Chilmark were puzzled by it, including Alexander Graham Bell, who conducted genealogical research on Martha’s Vineyard in the 1870s in an attempt to isolate the cause of the deafness. “If you look at his research notes … it’s basically page after page of, ‘This person was this person’s grandfather and this was his great-grandfather,” Van Riper said. Mendelian genetics hadn’t yet gone mainstream, “so the actual details of how conditions like deafness were inherited from one generation to another were very poorly understood.”

To the people of Chilmark, though, the remarkably high concentration of deafness wasn’t something that needed to be understood, because it wasn’t remarkable at all. Largely cut off from the rest of the world, they didn’t know the difference.

“These were small-time farmers and coastal fisherman, and by and large they didn’t leave written records of their thoughts behind. It may well have been that they sat around the fire at the end of the day shooting the breeze and said, ‘Why do you suppose it is?’” Van Riper said. “On the other hand, there’s reason to think that it never occurred to them to ask the question.”

* * *

Among the islanders, signing was considered a life skill, like knowing how to fish, more than a formal language to be taught. “It was passed on to kids as part of, ‘Here’s the stuff you need to know to make a living in this corner of the world,’” Van Riper said. Children picked it up from their parents; no records indicate that it was ever taught in schools.

No records, in fact, indicate much of anything about Martha’s Vineyard Sign Language. Nearly all that’s known about it has come from oral histories from people who lived during the peak of the island’s deaf population. The last known person with Lambert’s hereditary deafness, Katie West, died in 1952, and the pool of hearing people who still know the language is dwindling. There are no photographs, videos, or diagrams that preserve it.