20th

Good morning, student. I hope you have been able to read the two books about speech and hearing problems that I put in the library. Today’s lecture deals with the presence of the unusually large deaf population that existed on Massachusetts Island of Martha’s Vineyard for three centuries. From the settlement of the island in the 1640s to the 20th century, the people there, who had descended from 30 original families, married mainly other residents of the island. They formed a highly inbred group, producing an excellent example of the genetic patterns for the inheritance of deafness. Indeed in the late 1800, this island as a whole had a deafness rate 17 times greater than that of the rest of the United States.
     Even Alexander Graham Bell, the inventor of the telephone and the prominent researcher into deafness, visited Martha’s Vineyard to study the population. But because the principles of the genetics and inheritance were still unknown, he was unable to explain the patterns of deafness and why a deaf parent did not always have deaf children.
     In tile 20th century the local population has mixed with people off the island and the rate of deafness has fallen.