Hello yehudayona and all,
I wanted to mention that the book takes great pains to emphasize that what the author is talking about are genetic indications of Jewishness and various smaller groups within the larger whole (e.g., Levites and Cohanim). Dr. Ostrer has concerns that the genetic findings could potentially be used to exclude people from various Jewish groups when these people have always understood from family history and in Halachic terms that they were Jews and/or members of certain smaller Jewish populations. He is emphatic that genetics should not replace Halachic determinations. His great passion for genetics of the Jewish people seems to be about preventing suffering from certain illnesses and conditions that have been and continue to be linked with various genes.