Blood Tests and DNA – Part One by Rabbi Chaim Jachter


This week, we shall begin a four part series discussing the admissibility of blood tests and DNA as evidence in Beit Din.  In the first installment, we shall discuss the admissibility of blood tests in Beit Din.  We shall go on to review four rulings regarding DNA evidence that were issued before the World Trade Center terrorist attacks.  Afterwards, we shall discuss why Poskim accept DNA evidence to identify the remains of missing husbands from the World Trade Center and other disasters.  In the final essay, we shall examine the implications of DNA evidence on the Halachot of Mamzeirut. 

Blood Tests to Determine Paternal Identity – Majority Opinion

Since the early twentieth century, Poskim have been faced with the question of whether blood tests are admissible evidence in Beit Din to determine paternal identity.  In many countries, blood tests were commonly used as evidence that a husband was not the father of his wife’s child.  Most Rabbanim ruled that such evidence is inadmissible in Beit Din.  It seems that Rav Ben Zion Chai Uzziel (the Sephardic Chief Rabbi in Eretz Yisrael from 1936-1953) was the first to address this matter (Shaarei Uzziel 2:40:1:18).  He rules that blood tests are not admissible evidence based on the celebrated Gemara (Niddah 30a) that states that there are three partners in the creation of a person- Hashem, mother and father.  The Gemara goes on to explain what each partner contributes to the creation of the child.  The mother, states the Gemara, contributes the red material from which blood is created.  Rav Uzziel concludes from this that Chazal believe that blood type is determined exclusively by the mother.  Thus, argues Rav Uzziel, the modern scientific belief that blood type is influenced by both mother and father contradicts Chazal.  Rav Uzziel claims that the Halacha is determined by Chazal’s belief and not by scientific assertion, and he accordingly rules that blood tests are not admissible evidence regarding paternal identity.

Most Poskim agreed with Rav Uzziel’s ruling.  These authorities include many of the great Dayanim of the twentieth century, including Dayan Ehrenberg (Teshuvot Dvar Yehoshua 3: Even HaEzer 5; Dayan Ehrenberg was the leading figure in the Tel Aviv Beit Din for many decades.  When I visited the Tel Aviv Beit Din in 1992 to watch its Get administration, Dayan Ehrenberg, who died in 1976, was often quoted as the authoritative figure in determining Halachic policy), Rav Eliezer Waldenberg (Teshuvot Tzitz Eliezer 13:104), Rav Ovadia Yosef (Teshuvot Yabia Omer 10 Even HaEzer 12 and 13) and Rav Shalom Messas (Teshuvot Shemesh UMagen 3: E.H. 17-18; Rav Messas was the Sephardic Chief Rabbi of Yerushalayim from 1973 until his death in 2003 and is regarded as the leading Halachic authority for Moroccan Jews). 

Rav Waldenberg adds that scientific approaches are very much subject to change, and that which is accepted today is often rejected soon after.  This skeptical attitude towards scientific conclusions is commonplace in rabbinic thought throughout the ages, as Rav Waldenberg notes (for a summary of the Halachic literature regarding the admissibility of scientific evidence regarding Halachic matters, especially Hilchot Niddah, see Nishmat Avraham Yoreh Deah pp.82-85).  Therefore, Rav Waldenberg (writing in 1977) echoes the ruling of many rabbinic judges that we accept the divinely inspired assertions of Chazal of which we are certain, and not scientific assertions which are subject to revision. 

Indeed, Rav Kook (Teshuvot Daat Kohen number 140) notes the Halacha (Shulchan Aruch Orach Chaim 618:1) that if a doctor determines that a patient will not endanger his life by fasting on Yom Kippur and the patient disagrees, we permit the patient to eat on Yom Kippur, even though the Halacha also permits the patient to eat in the reverse case (where the patient insists that he need not eat and the doctor states that he must in order to preserve his life).  Rav Kook concludes from these Halachot that we regard scientific knowledge as only possibly correct.  We must consider both the possibility that the doctor is correct and that he is incorrect, and therefore in both instances the patient is instructed to eat on Yom Kippur (Safeik Nefashot LeHakeil).   

Blood Tests to Determine Paternal Identity – Minority Opinion  

Not all Poskim agree with this approach.  Rav Yitzchak Herzog (who served as Chief Ashkenazic Rabbi of Eretz Yisrael from 1939-1959) argues (in a letter published in Assia 35) that rabbis who adopt this approach are “sticking their heads in the sand” and ignoring scientific facts.  Rav Shlomo Zalman Auerbach (cited in Nishmat Avraham E.H. 4:1) notes that the Gemara in Niddah 30a need not necessarily be interpreted as teaching that blood type is determined exclusively by the mother.  It could be understood as teaching that the mother merely provides the catalyst for the production of blood, thereby leaving open the possibility of paternal influence on blood type even according to Chazal.

Rav Shlomo Dichovsky (a leading contemporary Dayan who sits on the Israeli Rabbinate’s Rabbinic Court of Appeals) notes that the Rambam (Moreh Nevuchim 3:14) and the Tashbeitz (1:163-165) write that the many medical assertions that appear in the Gemara are not derived from divine sources but rather from the medical knowledge of the time.  According to this approach, the accepted scientific evidence of the time should constitute admissible evidence in a Beit Din hearing.  Rav Dichovsky notes, though, that the Rivash (number 447) disagrees with the Rambam and Tashbeitz and argues that the medical assertions that appear in the Gemara are in fact divinely inspired just like the rest of the Talmud.  For a summary of the debate regarding the nature of Chazal’s medical claims, see Elli Friedman’s article on the subject available at

Incidentally, this approach of the Rambam to scientific claims in the Gemara is not rejected as heretical (as some have claimed in the recent controversy surrounding the publication of the books of Rav Natan Slifkin).  No less of an authority than Rav Dichovsky, a Chareidi Rav who sits on the Rabbinic Court of Appeals in Yerushalayim, regards the Rambam as a viable opinion and considered it in a ruling he issued in 1982.  The Tel Aviv Beit Din (cited in Assia 35) makes the same assertion as Rav Dichovsky.  Rav Dichovsky also cites two important late twentieth century Rabbanim, Rav Aharon Preiss (Mishnat Chassidim to Sefer Chassidim 1:291) and Rav Chaim David Regensburg (Mishmeret HaChaim number 37), who adopt this approach.  These opinions are cited in Nishmat Avraham (Even HaEzer 1:32-33), a highly regarded and widely read Sefer which bears Haskamot from eminent Rabbanim such as Rav Yehoshua Neuwirth. 

Rav Saadia Gaon’s Blood Test

It seems to me that another major consideration lurks beneath the ruling of the majority opinion of Dayanim who do not accept blood tests as admissible evidence in Beit Din.  A fascinating case involving Rav Saadia Gaon is recorded in the Sefer Chassidim (number 232).  The case involved a wealthy man who traveled a long distance with his pregnant wife and his slave.  The man died and the slave presented himself as the wealthy man’s son and was awarded the fortune by the local authorities.  The wife gave birth, and when the child came of age he went to Rav Saadia Gaon to complain about what the slave had done.  Rav Saadia Gaon exhumed the body of the father and removed one of the bones.  He took blood samples from both the son and the slave and placed the bone first into the blood from the slave and then into the blood of the son.  The bone absorbed the son’s blood but not the slave’s blood, thereby proving, in Rav Saadia’s opinion, the identity of the true son, since the bone absorbing blood demonstrated genetic similarity. 

The Eliyahu Rabba (an important Acharon often cited by the Mishnah Berurah) cites this story (chapter 568), but poses a question based on an incident recorded in Bava Batra 58a.  The Gemara records that a couple had ten children, but on his deathbed the husband said that only one of his sons was truly his child.  In order to determine who should inherit the estate, Rav Benaah devised an interesting plan.  He instructed the boys to hit their father’s grave, which would reveal the identity of the true child.  All of the boys hit the grave except for one, and Rav Benaah awarded the estate to the boy who did not hit the grave.  Rashbam (ad. loc. s.v. Amar Lehu) explains that the decision was an example of “Shuda DeDayni” (loosely translated as a Solomonic decision), as the true son would not have the audacity to hit his father’s grave (for further explanation see Kiddushin 74a Tosafot s.v. Shuda DeDayni). 

The Eliyahu Rabba wonders why Rav Benaah had to employ Shuda DeDayni if he could have used Rav Saadia Gaon’s blood test in order to determine who the son was.  The Rashash (commenting on the Rashbam ad. loc) asserts that Rav Benaah did not want to administer this test since it would reveal that nine of the boys were Mamzeirim.  Rav Benaah’s test merely revealed that one of the boys was a more refined person than his siblings, but did not necessarily prove the other siblings’ illegitimacy.  The Rashash bases his explanation on the Rambam and Bartenura’s comments (s.v. VeKirvah) to Eiduyot 8:7 that Mamzeirut should not be publicized. Rav Yosef Shalom Elyashiv (Kovetz Teshuvot 1:135) accepts Rashash as normative Halacha. 

An explanation of this approach is that a problem of Mamzeirut exists only when one has knowledge of the Mamzeirut, but one has no obligation to reveal such knowledge.  This approach is based on Kiddushin 71a, the Ran (Kiddushin 30 in the pages of the Rif s.v. Tannu Rabbanan) and Rama (E.H. 2:5; see the comments to this Rama summarized in the Otzar HaPoskim ad. loc.).  Indeed, in 1989 Rav Hershel Schachter showed me an article written by Rav Elchanan Wasserman supporting this approach, and he issued a ruling based on it in 1992.  Rav Aharon Lichtenstein told me (also in 1989) that the practice of many Rabbanim in pre-war Europe was to leave a locale when they heard that someone they knew to be a Mamzer was about to be married.  Indeed, my father-in-law Rav Shmuel Tokayer told me that Rav Moshe Feinstein advised him to conduct himself accordingly in a similar situation that he encountered when he served as a Rav in the 1960’s.  The Gemara refers to this lenient approach to Mamzeirut as a Tzedakah that Hashem does for Am Yisrael.  

It appears to me that this is a motivation behind the Dayanim’s refusal to admit blood tests as evidence of fatherhood in Beit Din.  They choose, as Rav Benaah did, not to administer a test that could potentially reveal that people are Mamzeirim.  It seems to me that the Dayanim did not wish to admit blood tests as evidence even in a case where Mamzeirut was not involved, since once we let the proverbial genie out of the bottle we cannot “put it back in.”  Accordingly, the consensus opinion among Dayanim was to avoid the use of blood tests, as its potential cost far outweighs any of its benefits.  It seems that the Gemara in Niddah 30a merely served as a Halachic basis for the Rabbanim to reject the use of blood tests but not as their main motivation to do so.  We should note that this type of an analysis of Rabbinic rulings is used by Rav Soloveitchik (cited in Nefesh HaRav pp.12-14) in a different context.

Next week, we shall (IY”H and B”N) present four rulings regarding DNA evidence that were issued by Poskim prior to the World Trade Center murders.

Blood Tests and DNA – Part Two by Rabbi Chaim Jachter

Do Walk-In Closets and Porches Require a Mezuzah? by Rabbi Chaim Jachter