DNA and Jewish Law

Question

Why isn't DNA seen as a valid source of Halachic decision making? Is it because it's too small for the naked eye? A margin of error problem? What?

Normally, physical evidence is plenty of information to make halachic decisions off of. For example, a piece of unmarked meat found in a Jewish neighborhood is assumed kosher, because it's in a Jewish neighborhood. And the gemorah responds, to the person who says he wished he had a drawing tablet to draw the tzizit of the generation of the desert, by saying that if he had just memorized it in his head, that would have been good enough!

Source for the question: http://www.jewishpress.com/pageroute.do/49607

Some of the authors in Contending with Catastrophe recount that several rabbis deliberated at length concerning the reliability of DNA evidence in identifying dead bodies or body parts (with a few even coming to the conclusion that it cannot be relied upon exclusively). Isn't the reliability of DNA evidence a well-known fact that was settled by scientists and statisticians a long time ago? How is it that rabbis in 2011 are spending their time on this matter? Don't their actions give ammunition to those Jews who argue that rabbinic leaders are behind the times?

Answer 1

I haven't studies the sources inside, but a couple observations, and some places to do more research:

• There are several different ways that DNA may be used in Halacha, and these ways may have different laws.

  • There's using DNA for paternity tests in cases of inheritance, which may (or may not) be different than paternity cases that concern Mamzerut. In other words, the Halacha of DNA may (or may not) be different depending on whether or not it is a judgment of money or a judgment of lineage.
  • There's also using DNA to prove that someone did or didn't murder someone. This would be used to either contradict existing witnesses or instead of witnesses. [which may, (or may not), have different Halachot].
  • There may also be other uses that I'm missing.

• With regards to the meat. In Halacha there is a difference whether the Meat is found on the street (where we say it is permitted, since we go after the majority) and whether the meat was bought in one of the stores and the person forgot which store (where we say it is forbidden, since there is an equal probability that the person went into each store - either he did or he didn't). In halacha, these two possibilites are referred to as kol d'parish me-ruba parish and "kol kavua k'mechtsah al mechtsah dami" - see this article for a thorough breakdown [I haven't read the whole thing]. - It may very well be that DNA is considered "kavua", and if so, even the 99.9% certainty of DNA would still be considered 50/50 halachically (and again, there may be halachic differences if money or lineage is being determined.)

• I glanced at the Talmud in Ketubot 15A, and the Gemara seems to say pretty strongly that normal leniences of majorities don't apply when it comes to lineage (Yuchsin), although I didn't really study it in depth and that may not be the conclusion.

Here are some places online that point to sources that discuss DNA in Halacha, (I haven't looked at them in depth). Follow the sources and see what they say about DNA:

• Blood Tests and DNA - by Rabbi Chaim Jachter (links from archive.org): part 1, 2, 3, 4. - These articles were also printed in Gray Matter vol 3, and can be read on Google Books. In this series of articles, Rabbi Jachter mainly focuses on the use of DNA in paternity testing, in particular if it can be compared to blood testing for paternity testing, which is discusses in Halachic sources. It also discusses the use of DNA testing to permit Agunas after the World Trade Center Attacks, and finishes off with the discussion of whether even the Rabbis who permit DNA testing for paternity would permit using it to prove Mamzerut.
• Shas Daf: DNA in Halacha - brings different halachic opinions about the acceptance of DNA in halacha
• R' S.Y. Zevin in L'Ohr HaHalacha (discussed in the Shas Daf article)

Answer 2

I think R' Broyde answered it pretty well. Technology progresses quickly, it takes time for everyone to be willing to fully accept the latest results. Not everything always ends up being certain as once thought, so sometimes some rabbis are a bit extra conservative and cautious. Also, many rabbonim are willing to rely on DNA evidence alone, so it is "seen as a valid source of Halachic decision making".

Answer 3

In terms of the case of the quote of your question, when it comes to identifying a dead body for the purpose of permitting the wife/widow to remarry, there was an argument put forth to not use DNA for such. It went as follows:

The strength of DNA results is in the matching up of several loci. A match between two DNA samples in one location is not very significant. Therefore, it is only the combination of several pieces of information, each of which on their own are not overwhelmingly significant, that creates the incredibly low chance of a false-positive. (Disproving a match, on the other hand, requires much less.)

That being the case, a possible problem arises in using this information for aguna cases. The halacha in testimony for an aguna is that while a siman muvhak, a single definitive marker, is enough, non-definitive markers do not combine, no matter how many there are (Rema Even Haezer 17:24). There is a dispute if this only excludes low-quality markers (Beis Shmuel #73), or even average markers (Chelkas Mechokek cited in Beis Shmuel). However, my (brief) research seemed to indicate the odds of any one location match to be about 8%, which is not at all a significant statistic (about 1 in 12!). This being the case, the DNA evidence, which relies on the combination of non-definitive markers, would be invalid.

I would note that many prominent authorities have explicitly said that DNA evidence is valid. R' Elyashiv, cited by Nishman Avraham E.H. 4:14 (along with R' S.Z. Aurbach), R' Z.N. Goldberg in several letters, and I was present when R' Moshe Heinemann said as much.

Answer 4

Scientists usually throw the number one trillion in regards to how many possible distinct dna possibilities for humans.

This would mean that statistically one in 140 people has a "dna twin".

Given that testing relies on the words of pasul eidos, the fact that usually they only have a partial sample and the reality that paternity tests rely on similarity as opposed to "identicality"; the question should be why some do rely on DNA evidence