Book Review: David Kaye’s The Double Helix and the Law of Evidence

The Double Helix and the Law of Evidence by David H. Kaye.  Harvard University Press: Cambridge 2010, pp. 352. $45.00.

“If it doesn’t fit, you must acquit.”

— The late Johnny Cochran, September 1995.

Almost fifteen years have passed since O.J. Simpson was acquitted of the double murder of Nicole Brown Simpson and Ronald Goldman.  Called the trial of the century, the Simpson case is still seen as a key point in legal history, even though the case created no significant legal precedent.

Experts at the time were still debating fundamental questions about the reliability,  acceptance, and admissibility of DNA testing.  The Supreme Court had handed down its watershed opinion in Daubert only a few years earlier.  As Professor David Kaye explains in his new book The Double Helix and the Law of Evidence, Simpson’s attorneys challenged the admissibility of the DNA evidence on numerous grounds.  But, at the end of the day, the most memorable moment of the trial is not the arcane issue of whether experts correctly calculated genetic probabilities using statistical estimation methods but Johnny Cochran’s statement in his closing, “If it doesn’t fit, you must acquit.”

Professor Kaye, distinguished professor of law and Weiss Family Faculty Scholar at Penn State Law, offers far more than just an account of the Simpson DNA evidence.  Kaye provides an in-depth review of how the law of DNA evidence progressed from its beginnings in the 1980’s to its current state.  His book is, in his own words, “part history, part legal analysis, part popular science, and part applied statistics.”  Kaye provides vignettes of many key developments in DNA evidence, from the first conviction and first exoneration based on DNA evidence in the 1986 Pitchfork case to the Simpson case to the use of mitochondrial DNA in analyzing the remains of Tsar Nicholas II and his family.  Kaye also examines legal milestones, such as People v. Castro, 545 N.Y.S. 985, 999 (Sup. Ct. 1989), in which Barry Scheck and Peter Neufeld convinced Judge Gerald Scheindlin to restrict the admissibility of the prosecution’s DNA evidence because the private testing laboratory “failed in several major respects to use the generally accepted scientific techniques and experiments for obtaining reliable results, within a reasonable degree of scientific certainty.”

Kaye’s book is not what I expected from the title, but surprises can be pleasant, as was this one.  Kaye draws from his substantial experience and his prior legal scholarship to create a concise and highly readable text devoted to the basics of DNA evidence and its historical development.  The book is not a comprehensive analysis of legal precedent governing DNA evidence, but that was not Kaye’s goal.  As Kaye explains, his work “is a tale of scientific egos, journalistic hype, lawyerly maneuvering, and judicial doctrine and disposition.”  Kaye starts the tale with biological evidence before DNA, such as the common A, B, and O blood types, and moves through the various stages of how courts and litigants reacted to the new actor on the legal stage.

Kaye’s explanations of the intricacies of DNA evidence are accessible to lawyers not having any specialized scientific training.  Kaye details the contributions of the major players, including experts such as Richard Lewontin, Daniel Hartle, and Eric Lander, lawyers Scheck and Neufeld, and the 1992 and 1996 reports of the National Research Council.  Kaye similarly explains the now classic “prosecutor’s fallacy” as applied to DNA evidence.

A fundamental question is whether certain differences in probabilities of guilt or innocence based on DNA evidence matter.  What struck me, particularly when reading certain sections dissecting the legal arguments pertaining to genetic probabilities, was whether jurors can rationally distinguish between various degrees of certainty in DNA testing.  From a reasonable juror’s perspective, is there any meaningful difference between one-in-a-million odds version one-in-a-billion odds?  Perhaps the average person cannot cognitively discern any difference between such odds.  Furthermore, the fact that Cochran’s mantra pervaded the theme of the Simpson trial underscores the effect of personal perceptions on conclusions about scientific evidence.  Other evidence may overshadow real and substantial disputes about the DNA evidence.  How jurors view the evidence is the ultimate question in any jury trial.  And what’s now called the “CSI effect” certainly colors (or taints?) the juror’s perspective.  See, e.g., Hon. Donald E. Shelton, et al., Study of Juror Expectations and Demands Concerning Scientific Evidence: Does the CSI Effect Exist?, 9 Vand. J. Ent. & Tech. L. 331 (2006-2007).

At the start of the book, Kaye recognizes that his “conclusions are colored by my own biases and beliefs, including the conviction that it is possible to grade, at least roughly, the truth of competing claims about what is scientifically known and unknown.”  Kaye touches on the issue of jury perception of DNA evidence near the end of the book with some discussion of jury experiments and jury polling.  But, for me, this is one of the most intriguing questions about DNA evidence, which often reduces to a simple statistical data point.  Statistics are built on assumptions in data gathering and analysis, and thus have inherent margins of error.  Understanding when a juror can comprehend statistical distinctions and when certain statistical evidence is overly persuasive is crucial to ensuring that the legal process achieves justice.

Indeed, perception and personal experience often are the determinative factors in how one views a historical fact.  Consider, for example, the discovery of DNA.  Ask the average trivia buff who the father of the genetic code is, and the answer you’ll probably receive is “Watson & Crick,” for James Watson and Francis Crick.  But that answer is wrong.  Those two Nobel laureates discovered the structure of DNA, which was groundbreaking, of course.  But the structure did little in setting the stage for DNA profiling and genetic analysis.  DNA’s potential as a powerful evidentiary tool began only when Marshall Nirenberg discovered the genetic code.  Nirenberg, along with Robert W. Holley and H. Gobind Khoran, won the Nobel Prize in 1968 for this work.  The father of the genetic code passed away earlier this year, but the public’s recognition of his legacy may not change.

Towards the end of the book, in a chapter titled “Learning from DNA,” Kaye explores the broader issues of evidence relating to nascent technologies, and what can be learned from the courts’ experiences with DNA evidence.  Will courts make the same errors when considering the admissibility of new technologies, such as facial recognition software or brain scanning technologies?  Will the ability to identify liars by microexpressions someday achieve “general acceptance”?  Those specific questions are beyond the scope of Kaye’s book, but the history of DNA evidence Kaye details will inform future debates about new types of scientific evidence.  In the words of Harry Truman, “The only thing new in the world is the history you don’t know.”  Or as Ziggy Marley crooned, “If you don’t know your past, you don’t know your future.”

One issue on which Kaye’s views would be particularly enlightening is the possible creation of a national DNA database.  In early March, President Obama announced his support of a national DNA database during an interview with John Walsh, host of the popular America’s Most Wanted show and father of murdered six-year-old Adam Walsh.  Not surprisingly, the database proposal has its proponents and opponents.  If abused, a national DNA database could raise significant privacy concerns.  One also has to weigh the detrimental effects of false positives—that is, people incorrectly identified as criminal suspects based only on an incorrect DNA test result.  At the same time, using an investigative tool as powerful as DNA profiling can conserve scarce resources, particularly when many local governments are reducing law enforcement budgets.  Kaye has written on the topic, see Rounding Up the Usual Suspects: A Legal and Logical Analysis of DNA Database Trawls, 87 North Carolina Law Review 425 (2009), but he leaves it for a subsequent book, which may be coming sooner rather than later.  Technology advances and inexpensive computing will, before long, pressure lawmakers to implement some form of a comprehensive DNA database for criminal purposes.

Overall, Kaye provides a highly readable volume about the development of DNA as legal evidence.  As a former-scientist-turned-lawyer (who now lives vicariously through my scientist/professor wife for my science fixes), I thought Kaye’s book struck an excellent balance between law, history, and science.  The Double Helix and the Law of Evidence offers something for lawyers and non-lawyers alike (including judges and judicial clerks), and should be a particularly welcomed resource for an upper-level seminar class in law school.


Matthew J. Dowd is an attorney at Wiley Rein LLP.  He represents clients in appeals before the U.S. Court of Appeals for the Federal Circuit and in district court litigation, including patent and general commercial litigation.

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1 Response

  1. Dave Hoffman says:

    Helpful & incisive review. Thanks!