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Evolution in Court

FERNÁNDO GONZÁLEZ CANDELA/ PHOTO: MIGUEL LORENZO. 31/07/2013 When Galileo Galilei, Giordano Bruno or Miguel Servet, among others, were put on trial, they were tried in ecclesiastical courts, not civil courts, and mostly they were convicted based on religious clashes...

VALENCIA. Scientific theories are not tried in the courtroom, or at least they have not been for several centuries. When Galileo Galilei, Giordano Bruno or Miguel Servet, among others, were put on trial, they were tried in ecclesiastical courts, not civil courts, and mostly they were convicted based on religious clashes and not necessarily due to heresy arising from new scientific theories. There is one notable exception: the theory of biological evolution, formulated by Charles Darwin and Alfred R.Wallace in the mid nineteenth century. Evolutionary theory is regularly questioned in U.S. courts at all levels, which have shed doubt on its validity as a scientific theory worthy of inclusion on secondary education curricula. But here we are concerned with its presence in the courtroom in quite another context.

Evolution has been appearing in court since the 1990s. In a growing number of cases, evolutionary biologists are called to testify as expert witnesses in civil and, occasionally, criminal lawsuits. There is a common thread joining them all: the transmission of an infectious agent, usually a virus such as human immunodeficiency virus (HIV) or hepatitis C virus (HCV) from a common source to one or more infected recipients. Given the severity of these infections, which can lead to the patient's death, people generally seek compensation in court for physical, psychological and economic damages. Frequently the source is related to a medical procedure, a transfusion with contaminated blood or another substance, or the use of an unsterilized product or equipment, but we also find cases of malpractice, even criminal acts.


In the late nineteen eighties, the AIDS epidemic spread unchecked through many different countries and communities. Then there were no drugs available to slow down the progression of AIDS and its diagnosis represented little more than the announcement of imminent death. It was known that the disease was caused by a retrovirus and that it was passed from person to person through bodily fluids, especially blood, but could also be transmitted by intermediate vectors, such as hypodermic needles. Then HIV infection was diagnosed in a woman who did not engage in any known risk practices, and this led to an investigation that pointed to her HIV-positive dentist as the possible source of infection. Until that time it was not thought possible for HIV to be transmitted through dental instruments, thus no safety measures were taken.

The woman in question decided to take a civil action against her dentist, and sue him for damages. The case became more complicated when it was discovered that six other patients of the same dentist were also infected with HIV. The question now was no longer whether, or not, the first patient had been infected by the dentist, but how many and which patients had been infected by him, as some of them did engage in risk practices. To answer this, an expert team was called in, which sequenced a fragment of the viral genome in samples obtained from both the dentist and his patients, and 35 other people unrelated with them but also infected with HIV.

The judge in charge of the case was not competent enough to take a decision on the validity of the evidence presented. Basically, a phylogenetic study linked samples from five patients, including the first petitioner, with the dentist but ruled out the other two, whose source of origin was undetermined. Therefore the following resolution was adopted: the judge would accept the validity of the test if the scientific community ratified it. To do so, the results should be communicated in the usual way, as a scientific article to a peer-reviewed journal, and thus be submitted to the appropriate scrutiny and evaluation before publication. The article was published in the journal Science on May 22, 1992 (Ou et al., 1992) and the dentist was condemned to compensate five of the victims for damages.

Unlike other genetic evidence commonly employed in court cases, here it did not seek to establish identity between the alleged victims' genetic data and that of the source of infection, but rather to distinguish between their common co-ancestry and the possibility that they came from other sources, which were not identified in the general population. All this could be revealed by analysing the differences found between the corresponding gene sequences. Since then, there have been countless cases where we have used the rapid evolution of viruses, like AIDS, to settle claims related to person-to-person infection or infection through medical procedures. On occasion, proceedings have been held in a criminal court, rather than a civil one, as in the case of Richard Schmidt, a physician from Louisiana State (U.S.A.) charged with attempted murder.

This American doctor used blood infected with human immunodeficiency virus and hepatitis C virus from one of his patients to transmit these diseases to his former lover, who had decided to break off their relationship (Metzker et al., 2002). Although both viruses were transmitted to the recipient, the prosecution relied on the HIV study to demonstrate the connection. Indeed, numerous advances can be witnessed in the decade separating this case and the case of the Florida dentist, both in terms of the methodology employed and the courts' acceptance of this evidence. However, it should be mentioned that in both cases doubts were raised about the statistical validation of the results, especially given the importance of the findings.

One solution to this problem is the use of statistical methods that are more advanced than the pseudorandom re-sampling (bootstrapping) used until that time. Specifically, the introduction of maximum likelihood estimates of trees means alternative hypotheses can be compared on a solid statistical basis. In fact, two of the authors of reference in forensic genetic applications propose the application of Bayesian inference, based partly on calculating the plausibility of a hypothesis from the available evidence, to report on the likelihood that certain biological elements come from the accused, or not (Evett and Weir, 1998). To do this, the researcher must calculate the probability of observing the data they have under different assumptions as to how these data might have been generated. 


Our research group has had occasion to employ these procedures in what is probably one of the most complex cases of applying evolutionary theory to expert forensic evidence (González-Candelas et al., 2013). In February 1998, an outbreak of hepatitis C viral infection was discovered in Valencia, which was quickly attributed to the less than negligent work performance of the anaesthetist Dr. Juan Maeso. The so-called «Maeso case» went on for almost 10 years, during which the extensive judicial investigation was followed by a trial in the Provincial Court lasting over a year, with a subsequent appeal to the Supreme Court.

As a result the defendant was sentenced to almost 2,000 years in prison for malpractice leading to the infection of at least 275 patients, five of whom had died by the time the trial was held. In this case, the problem was aggravated by the sheer dimension of the outbreak, the largest as yet, which came from the same source over a time period, which had to be determined (it proved to be almost ten years). During this time, the virus had continued to evolve at the source, so it was quite different in the population infected at first from those affected towards the end.

The hypothesis on which we based our report was the same as in previous cases: if transmission had occurred from a common source, then the viruses isolated from these patients would share with each other and with the viruses isolated from the source, a nearest common ancestor. This relationship would be closer than with any other viral population not linked to the source.

However, in this case we could not just test this hypothesis: it was necessary to establish which of the patients, numbering just under 400, treated by this anaesthetist and diagnosed with HCV infection of the same type, had been infected by him and which ones had been infected from other sources. It is estimated that about 2.5% of the Spanish population is infected with HCV, although many of those infected are unaware of their status as the virus may be latent, without causing apparent disease for years. Notwithstanding it can still be transmitted in this «dormant» state.

Full text available at Mètode's website


Fernando González Candelas. Full Professor of Genetics. University of Valencia.

Photo: Miguel Lorenzo

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