Technologies of Population: Forensic DNA Testing Practices and the Making of Differences and Similarities

This article is about population. My aim is to answer the question, what is population? Instead of defining it myself or asking geneticists what it is, I want to trace population in genetic practices and to observe how it is embodied in them. Toward this end, I analyze a forensic case. My analysis results in two arguments: first, that geneticists cannot know the individual without a population; second, that in genetic practices neither the individual nor the population is inherently "biological"--both are technologically assisted categories.

Population is a category of debate specifically in the Human Genome Diversity Project, ¹ and in population genetics at large. Geneticists aim at achieving a consensus definition of what population is, in order to sample, study, and compare populations. In this article, however, I examine practices of population and attend to its variety in laboratories. In order to "know" a population, geneticists study the cell material of collections of individuals. In forensics, on the other hand, the vantage point is quite different. Forensic geneticists are interested in the individual: their aim is to identify individual A as similar to, or different from, individual B. Yet, I have chosen this very practice as a site for examining population. For, in order to know an individual, forensic geneticists apply a category of population as well. Hence, in order to produce differences (between individuals), geneticists need to presuppose similarities (within a population). I will examine practical decisions about individuality and population, and hence about similarities and differences. On the basis of one forensic case, various concepts of population will be interrogated.

Taking population as the main focus of my analysis, I will pay little attention to legal aspects of forensic DNA, a highly important matter in its own right. Rather, the site studied is a laboratory, the Forensic Laboratory for DNA research in Leiden. Since my argument is organized around a forensic case, the narrative unfolds as a "trip" back and forth between laboratory and courtroom, observing the process of identification and examining concepts of population embodied in the case.

In Court

We are in a courtroom somewhere in the Netherlands. A murder case is in progress. Both the victim and the suspect are Turkish. The victim was kidnapped and killed. Evidence was found in a house next to the victim's body, and also in a car belonging to one suspect; the evidence material consists of traces, such as blood spots, chewing gum, and cigarette butts. The evidence at the scene of the crime indicates that more people were present. Other circumstantial evidence made the prosecutor suspect one person in particular. The main suspect has denied any involvement. Since the victim no longer has a voice, the question remains: can the suspect be identified as the perpetrator?

In court, a relatively new type of expert witness is present to help in the process of identification. ² This expert witness is a geneticist, called in to present and clarify the DNA evidence based on the suspect's cell material and on the evidence: the blood spots and chewing gum, and especially the cigarette butts. The DNA evidence consists of a DNA fingerprint with a number, 10^-7, which represents the likelihood that the evidence comes from any other person in the population; according to the expert witness, this number indicates that evidence and suspect DNA coincide. The DNA evidence supports the findings of the prosecutor that were based on other circumstantial evidence. The defense objects to the results of the DNA tests and questions the testimony based on a power of 10^-7.

In order to trace where the results presented in court came from, what they mean, and how they play a role, we may best enter the Forensic Laboratory. This site is of great importance to the significance of the DNA evidence presented in court. We will first consider this laboratory...