DNA as ‘ready-made evidence’: An analysis of Portuguese judges’ views

The introduction of biological evidence in judicial settings raises particular modes of entanglement between professional cultures and perceptions of the probative value of evidence. When DNA evidence reaches court, it also challenges the perceived margins of critical assessment of the work and understandings of previous links in the chain of custody, like the criminal police, forensic experts and the public prosecution services. Given the apparent neutrality of judicial institutions, how do Portuguese judges perceive and value biological evidence? And how do judges see their articulation with other operators of the criminal justice system? An analysis of 14 interviews carried out with Portuguese judges reveals the challenges in the evaluation of biological evidence, which is characterised as a ‘safe haven’, grounded as it is on an indisputable scientific authority. The suggestion of the presence of a cultural rift emerges, which, taken with the work of other epistemic cultures, leads to biological evidence being seen as ‘ready-made evidence’ on its arrival in court, thus limiting the role of judges in its appraisal.

A 3,000-year-old, basal S. enterica lineage from Bronze Age Xinjiang suggests spread along the Proto-Silk Road

Salmonella enterica (S. enterica) has infected humans for a long time, but its evolutionary history and geographic spread across Eurasia is still poorly understood. Here, we screened for pathogen DNA in 14 ancient individuals from the Bronze Age Quanergou cemetery (XBQ), Xinjiang, China. In 6 individuals we detected S. enterica. We reconstructed S. enterica genomes from those individuals, which form a previously undetected phylogenetic branch basal to Paratyphi C, Typhisuis and Choleraesuis–the so-called Para C lineage. Based on pseudogene frequency, our analysis suggests that the ancient S. enterica strains were not host adapted. One genome, however, harbors the Salmonella pathogenicity island 7 (SPI-7), which is thought to be involved in (para)typhoid disease in humans. This offers first evidence that SPI-7 was acquired prior to the emergence of human-adapted Paratyphi C around 1,000 years ago. Altogether, our results show that Salmonella enterica infected humans in Eastern Eurasia at least 3,000 years ago, and provide the first ancient DNA evidence for the spread of a pathogen along the Proto-Silk Road.

Projecting Ancient Ancestry in Modern-Day Arabians and Iranians: A Key Role of the Past Exposed Arabo-Persian Gulf on Human Migrations

The Arabian Peninsula is strategic for investigations centered on the early structuring of modern humans in the wake of the out-of-Africa migration. Despite its poor climatic conditions for the recovery of ancient human DNA evidence, the availability of both genomic data from neighboring ancient specimens and informative statistical tools allow modeling the ancestry of local modern populations. We applied this approach to a data set of 741,000 variants screened in 291 Arabians and 78 Iranians, and obtained insightful evidence. The west-east axis was a strong forcer of population structure in the Peninsula, and, more importantly, there were clear continuums throughout time linking western Arabia with the Levant, and eastern Arabia with Iran and the Caucasus. Eastern Arabians also displayed the highest levels of the basal Eurasian lineage of all tested modern-day populations, a signal that was maintained even after correcting for a possible bias due to a recent sub-Saharan African input in their genomes. Not surprisingly, eastern Arabians were also the ones with highest similarity with Iberomaurusians, who were, so far, the best proxy for the basal Eurasians amongst the known ancient specimens. The basal Eurasian lineage is the signature of ancient non-Africans who diverged from the common European-eastern Asian pool before 50,000 years ago, prior to the later interbred with Neanderthals. Our results appear to indicate that the exposed basin of the Arabo-Persian Gulf was the possible home of basal Eurasians, a scenario to be further investigated by searching ancient Arabian human specimens.

CHILDREN’S EVIDENCE IN SEXUAL CASES IN THE CONTEXT OF S v QN 2012 (1) SACR 380 (KZP)

This case note considers a number of issues in the context of the case of S v QN (2012 (1) SACR 380 (KZP)). These are: the competence of a childwitness, the admonishment of a child witness, the evaluation of evidence given by a child witness, the non-production of DNA evidence, and theprocedures followed regarding the use of an intermediary in terms of section 170A of the Criminal Procedure Act 51 of 1977.

Assessing the Forensic Value of DNA Evidence from Y Chromosomes and Mitogenomes

Y chromosome and mitochondrial DNA profiles have been used as evidence in courts for decades, yet the problem of evaluating the weight of evidence has not been adequately resolved. Both are lineage markers (inherited from just one parent), which presents different interpretation challenges compared with standard autosomal DNA profiles (inherited from both parents). We review approaches to the evaluation of lineage marker profiles for forensic identification, focussing on the key roles of profile mutation rate and relatedness (extending beyond known relatives). Higher mutation rates imply fewer individuals matching the profile of an alleged contributor, but they will be more closely related. This makes it challenging to evaluate the possibility that one of these matching individuals could be the true source, because relatives may be plausible alternative contributors, and may not be well mixed in the population. These issues reduce the usefulness of profile databases drawn from a broad population: larger populations can have a lower profile relative frequency because of lower relatedness with the alleged contributor. Many evaluation methods do not adequately take account of distant relatedness, but its effects have become more pronounced with the latest generation of high-mutation-rate Y profiles.