What is unusual about the island of Martha’s Vineyard?

Good morning. students. I hope you have been able to read the books about speech and hearing problems that I put in the list. [14]Today’s lecture deals with the presence of the unusually large deaf population that existed on the Massachusetts island of Martha’s Vineyard for about three centuries. From the settlement of the island in the 1640’s to the twentieth century, the people there，who were descended from only twenty-five or thirty original families, married mainly other residents of the island. They formed a highly inbred group, producing an excellent example of the genetic pattern for the inheritance of deafness. Indeed in the late eighteen hundreds one out of every twenty-five people in one village on the island was born deaf, and [15]the island as a whole had a deafness rate at least seventeen times greater than that of the rest of the United States. [16]Even Alexander Graham Bell, the inventor of the telephone and a prominent researcher into hearing loss, visited Martha’s Vineyard to study the population. But because the principles of genetics were still unknown, he was not able to explain the pattern of deafness and why a deaf parent did not always have deaf children. [17]In the twentieth century, the local population has mixed with people off the island and the rate of deafness has fallen.