DNA Testing

[xoxoxoBruce]

Unlike many of the police investigative tools, DNA testing, while slow and expensive, is at last a proof positive method.

Uh, no.

New York University law professor, Erin Murphy wrote a 23-page article for the Emory Law Journal, titled, "The Art in the Science of DNA: A Layperson's Guide to the Subjectivity Inherent in Forensic DNA Typing". link (pdf)

Often omitted from critiques of forensic methods, however, is a robust discussion of nuclear DNA typing. If anything, DNA typing is typically held out as the pinnacle of “good” forensic evidence, in that it exemplifies the kind of scientific rigor that first-generation techniques lack. After all, DNA analysis emerged from scientific processes, and it is a testable, reproducible, and falsifiable technique. DNA analysts even testify to their findings with expressions of statistical probabilities rather than arbitrary and unsupportable statements of certain identity.

Without question, this praise is well-deserved. DNA typing represents a marked advance beyond the shamanistic “sciences” of the first generation. Yet the seeming corollary—that DNA typing is therefore an exercise in purely objective, indisputable science—does not hold true.

This is not to suggest that DNA has no basis in objective science, or even that it is as subjective as other forensic techniques; comparing most first-generation methods to DNA typing is like comparing astrology to neuroscience. Nevertheless, not unlike neuroscience, the fact that DNA typing is scientifically grounded does not mean that there are not plenty of things that we still do not understand about it, and plenty of instances in which the best conclusions we can draw are nonetheless tentative ones.

Many people know this, but a surprising number of laypersons, and even lawyers, do not. To be clear, I am not saying that DNA typing done poorly entails an exercise of subjective judgment. Rather, DNA typing—done perfectly and precisely according to protocol—still often entails making discretionary calls and choices. But just because DNA typing is not wholly objective does not mean that it is wholly indeterminate—it simply means that it may be more like meteorology than mathematics.

Well that kind of throws a little reasonable doubt into the fray.