Read the passage. Sign Language on Martha's Vineyard
While researching Martha's Vineyard, an island off the coast of Massachusetts,
anthropologist Nora Groce made a remarkable discovery. She learned that from the
1600s until the early 1900s, almost all the residents of two towns on the island-West
Tisbury and Chilmark-were fluent in sign language. During these years, the towns had
an unusually high population of deaf people, due to a form of hereditary deafness that
ran in many Martha's Vineyard families. Consequently, a bilingual society developed. The
islanders didn't attend special sign language classes; they simply learned the language as
they grew up. One of the most interesting aspects of the phenomenon was that, in the
absence of language barriers, deafness was not perceived as a disability. As one
Vineyarder explained to Groce, deaf people were seen as "just like everyone else."
What is the main idea of the passage?