Proving Paternity – Part 1

  Identifying a person’s father and mother is of great significance in Halacha. A father is obligated to provide for his children; a child is commanded to honor both parents; and after the parents’ passing, the children mourn them and inherit their property. Determining Yichus also depends heavily on parental identity: Jewish status is determined by the mother; the status of Kohen and Levi passes from father to son; and if a married woman becomes pregnant by a Jewish man who is not her husband, the child is considered a Mamzer and is forbidden to marry within the community.

There are situations in which a person’s lineage is uncertain. For example, during divorce proceedings, a husband may claim that a child presumed to be his and his wife’s is not actually his and seek to be released from the obligation to support the child.

      Advances in scientific research have introduced several methods for establishing or ruling out parentage, each with distinct levels of reliability:

• Blood type testing is the most basic approach, comparing the ABO (and sometimes Rh) blood types of the child and the alleged father. Because blood type is genetically determined, certain parental combinations make specific child blood types biologically impossible. Where the child’s blood type contains elements inconsistent with the alleged father’s type, testing can exclude paternity with approximately 93% certainty.
• Tissue typing (HLA typing) examines the human leukocyte antigen system – the genetic markers responsible for immune and tissue compatibility – which a child inherits in equal halves from each parent. Because HLA markers are highly polymorphic and individually distinctive, the absence of any match between the alleged father and the child yields an exclusion probability of 98%–99.9%.
• DNA testing is the gold standard of paternity determination. By comparing specific DNA sequences, such as short tandem repeats (STRs), between the child and the alleged father, this method can establish or exclude paternity with results approaching 100% certainty. However, as we will see below, its halachic decisiveness may vary by context, even when the statistical certainty is extremely high.

The development of these technologies has sparked considerable debate among leading Poskim regarding their Halachic validity, with far-reaching practical consequences for the areas of Halacha related to parenthood mentioned above. A further application where such testing may prove especially significant is the relief of Agunos. When a person dies under tragic or violent circumstances, and the condition of the body renders conventional identification impossible, DNA testing may offer a means of establishing identity with sufficient certainty to permit the widow to remarry.

In practice, Poskim are divided on how to treat these tests, with a range of opinions. As we will see below, different areas of Halacha require diverse levels of certainty, and accordingly, the legal status of genetic evidence varies from one context to another. In this essay, we will examine some of the sources cited by Poskim in this debate and consider how leading Poskim have ruled on the matter.

The earliest source that is often cited in this context is the Sefer Chasidim (232), which recounts an unusual case involving R’ Saadia Gaon. A man once traveled abroad with his servant, leaving his pregnant wife behind. The man died, and the servant seized his estate, claiming to be his son. When the actual son grew up, he wished to reclaim the inheritance but feared confronting the servant, who had ties to the authorities. He eventually turned to Rav Saadia Gaon for help.

R’ Saadia devised an unconventional test: Blood was drawn from the son into one vessel and from the servant into another. A bone from the deceased was then placed into each vessel. When the bone was placed in the servant’s blood, nothing happened, but when it was placed in the son’s blood, it absorbed the blood. This was taken as proof of the son’s identity, based on the idea that a father and son are, in essence, one body, and thus the son’s blood would be absorbed by his father’s bone.^[1] Sefer Chasidim cites this story to support a ruling in the laws of mourning: a son should fast annually on the anniversary of his father’s death, reflecting the concept that father and son are considered as one Guf.

At first glance, this may suggest a precedent for using physical phenomena as evidence in questions of paternity, not only in matters of Isur v’Heter but also in financial disputes. Moreover, Sefer Chasidim derives a broader idea from this episode, namely that a father and son are considered “like a single body,” which is linked to the practice of fasting on the anniversary of a father’s death.

However, the Acharonim caution against relying too heavily on this source. To begin with, this is not an explicit discussion in the Gemara or a formal ruling in the classic Sifrei haPoskim, but a narrative brought in Sefer Chasidim. In addition, the nature of the test itself is unclear – how exactly did it work, under what conditions was it performed, and how would Halacha evaluate such a method? Finally, even if the story suggests a conceptual precedent for biological verification of paternity, it does not necessarily follow that it can be applied to all types of testing or to every Halachic context.

The Elya Raba (O.C. 568:15) cites this story and challenges it based on a passage in the Gemara (Bava Basra 58a). There, a man reportedly told his wife that only one of their ten sons was truly his. Before his death, he declared, “All my property goes to one son,” without specifying which. The sons came before R’ Bena’a for a ruling. He instructed them to go and strike their father’s grave until he would rise and reveal the intended heir. All of them went – except for one. Based on this, R’ Bena’a ruled that the one who refrained was the true son and awarded him the entire estate.

The Elya Raba asks: If there were a way to determine paternity through some physical test, why did R’ Bena’a not use such a method, instead relying on a behavioral test? By challenging the story of R’ Bena’a using the case of the Sefer Chasidim, the Elya Raba indicates that he considered its implications potentially relevant even to monetary matters. Nonetheless, it seems to stand in tension with the Gemara.

The Rashbam (in his comments to this Gemara) initially explains that R’ Bena’a assumed the illegitimate sons would be willing to strike the grave, while the legitimate son would refrain. But he then offers a different explanation: R’ Bena’a awarded the estate to the son who refused because his restraint showed he was the most modest and respectful. It was therefore reasonable that the father loved him most. But this raises a difficulty: Why didn’t the Rashbam say that R’ Bena’a identified him as the man’s true son?

The Rashash addresses this point and suggests that the Rashbam may have been aiming to resolve the question raised by the Elya Raba. The test attributed to R’ Saadia Gaon could indeed determine biological paternity. However, according to the Rashbam’s interpretation, R’ Bena’a was not trying to identify the biological son at all. Rather, he was trying to discern the father’s intent – namely, which son he wished to favor. To uncover that, a behavioral test was necessary; the kind of examination described by Rav Saadia would not have helped.

The Rashash offers an additional approach: even if a biological test could have identified the true son, perhaps R’ Bena’a deliberately avoided it because it would have definitively exposed which of the sons were illegitimate. By sending them to strike the grave, he avoided revealing anyone’s disqualification and instead identified the most refined among them. The Rashash concludes that this explanation is more convincing.

From the Rashash’s wording, it appears that, in principle, he regarded such a test as capable of establishing illegitimacy with certainty. As an aside, this idea – that one should avoid procedures likely to uncover a status of Mamzerus – is applied in contemporary Batei Din. In cases involving married couples, DNA testing is often avoided so as not to raise doubts or increase the number of individuals whose status could be called into question.

In Shu”t Minchas Asher (3:87), haGaon Rav Asher Weiss shlit”a discusses the halachic standing of DNA testing at length, and revisits the episode recorded in Sefer Chasidim in that context. He concludes that one cannot take that story as proof that such a test would be valid for determining Mamzerus.

To begin with, there are other plausible reasons why R’ Bena’a may have avoided such a procedure, even if it had no Halachic force in establishing lineage. For example, he may have wished to avoid desecrating the deceased. It is also possible that too much time had passed since the man’s death, making such a test impractical.

Furthermore, the Rashash’s explanation (that R’ Bena’a refrained from testing to avoid exposing the sons’ disqualification) remains relevant even if the test itself is not Halachically decisive. After all, even raising suspicion or casting doubt on their status would have profound consequences. For this reason, no definitive conclusion can be drawn from the Rashash regarding the halachic validity of such a test in determining Mamzerus.

The next stage of this discussion will address the fundamental principles at play in Halacha, examining the considerations raised by the Acharonim, particularly in the Teshuvos of Rav Asher.

[1] It is noteworthy that the standard of proof required to remove property from someone in possession of it is extremely high – typically, even a Rov is insufficient. Yet despite this, Rav Saadia relied on this test even in a financial dispute.