Free The People of the Eye: Deaf Ethnicity and Ancestry by Harlan Lane, Richard C. Pillard, Ulf Hedberg Page B

of the children in the "other" category would be recorded as hereditarily Deaf. Third, the "other" category can contain hereditarily Deaf children who have no Deaf relatives or ancestors whatsoever (as we explain later). Thus we have an estimate of three-fourths of the children in the ASL-prone subset were probably Deaf due to heredity.124
    A comparable result comes from a follow-up polling of parents whose children were included in the 1988 annual survey, where they were said to have become "profoundly hearing impaired" before age two without an environmental cause.'25 Replies identified whether each parent was hearing, Deaf, or status unknown; this yielded six mating types from which it was statistically estimated that 63 percent of these Deaf children were Deaf for hereditary reasons and the remainder for reasons unknown. Sixty-three percent is probably an underestimate of the importance of heredity since it does not take into account the hereditarily Deaf children with hearing parents but Deaf ancestors or relatives-in some cases even unknown to the family. As one investigator put it, "Limited knowledge of family history is frequently observed." 26 These estimates of two-thirds to three-fourths of the Deaf-World as being hereditarily Deaf are based on contemporary surveys. The figures could well prove quite different for the eighteenth and nineteenth centuries, when childhood illness (but also death from illness) was more common.
    When ancestry is taken in its most literal sense in the West-that is, the connection by blood of successive generations-it applies to all hereditarily Deaf people. No matter if the Deaf trait is expressed in every generation of their ancestry or if that expression skips some generations, the genetic heritage is always there in every generation. So most Deaf people in the United States today are hereditarily Deaf, but do they tend to share ancestors? As we will show, the practice of Deaf founding families to unite with others through intermarriage tended to proliferate the Deaf trait, expressed or unexpressed, down through the generations and thus their Deaf descendants had shared ancestry.127 There is a further reason why two hereditarily Deaf people are likely to have an ancestor in common. Suppose we knew the lineages of everyone back to Adam. We would see that, from time to time, a gene associated with being Deaf will originate here and there by random gene variation. The descendents of these originators will spread out geographically, down through the ages. The shared ancestry of those descendants will be all the more likely because any given gene will tend to spread locally since people tend to choose marriage partners who live nearby.
    So even if a particular gene is rare among the Deaf population in general, those who do have it will tend to form "islands" of kin related by common descent. After countless generations, the descent group of Deaf people with any given gene variant must be large indeed. As Parts II and III show, the Deaf descent group originating in the English county of Kent spread out in the United States to include Martha's Vineyard, then Maine, and on to other regions of the country. However, the DeafWorld in the United States is undoubtedly comprised of more than one such descent group with a common ancestor. Thus, "Deaf American" is like "Hispanic American"-an umbrella term that, based on shared language and culture, gathers numerous distinct descent groups, each with its own common ancestor.
    And what of Deaf ASL signers who are not hereditarily Deaf? Like Pashtun and Yao ethnicity, the Deaf-World includes unrelated members; those members qualify because they have the properties of Deaf people (visual orientation, sign language), acquired in childhood. Thus, there is biological unity, as well as linguistic and cultural unity, among the members of the Deaf-World. And as with the ethnic groups discussed above, these unrelated members of the Deaf-World are seen as