Browsing by Author "Gibbon, Victoria"

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    Assessment and improvement of current sex estimation standards for application in Holocene San and Khoekhoe populations
    (2022) Malek, Sadiyah; Gibbon, Victoria; Sealy, Judith
    Skeletal sex estimation is important in biological anthropology. Population-specific sex estimation standards do not exist for southern African Holocene San and Khoekhoe (HS-K) population. Due to their markedly small stature, skeletal gracility, and physically active lifestyle, they exhibit reduced sexual dimorphism. In this study I aimed to assess the accuracy of current sex estimation methods, and to optimise the assessed methods for population-specific application in the HS-K population. Seven morphological traits (cranial and mandibular) and six metrical parameters (mandibular, humeral, and femoral) were analysed in 175 adult HS-K skeletons. Accuracy was determined by comparison with pelvic sex estimates. Results were analysed using chi-squared tests, univariate statistics, and cross-validated discriminant function analysis. Trait/parameter preservation rates were assessed and reported: Of the traits, supra-orbital margin and glabella were best preserved (90% and 88% respectively), and mandibular shape least (71%). Of the metrical parameters assessed, femoral and humeral vertical head diameters (FVHD and HVHD) were best preserved (89% and 80% respectively), and bicondylar breadth (BB) least (44%). The highest sex classification accuracies obtained were for mastoid process (73%) and mandibular shape (72%), whilst the lowest were for mental eminence (53%) and nuchal crest (53%). Following categorisation by pelvic sex, the highest accuracies in females were for nuchal crest (98%) and mental eminence (95%), and in males, mandibular shape (80%) and gonial eversion/flaring (81%), illustrating differential sexual dimorphic expression for certain traits. All six metrical parameters were sexually dimorphic, with dimensions of FVHD and HVHD being the most discriminatory. The highest discriminant function accuracy for a single measurement (univariate) was 75% for FVHD, and for combined measurements (multivariate) were 77% for direct combination of BB, FVHD and HVHD, and 73% for stepwise combination of FVHD and HVHD. Whilst all traits/parameters assessed were sexually dimorphic, they produced lower accuracy rates than in other populations. This confirms that the range of sexual dimorphism exhibited by the HS-K does not conform to existing standards, illustrating the need for methodological adjustments. This study identified the most accurate areas to target for sex estimation in the HS-K and generated the first population-specific discriminant functions for sex estimation with known accuracies.
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    The effect of clothing and carrion biomass load on decomposition and scavenging in a forensically significant thicketed habitat in Cape Town, South Africa
    (2022) Jan Spies, Maximilian; Gibbon, Victoria; Finaughty, Devin; Friedling, Jacqui
    Estimating the post-mortem interval is important to help identify the deceased in forensic death investigations and requires biogeographically specific knowledge of the rate of decay. Decomposition is influenced by numerous variables, including clothing, climate, and vertebrate scavenging guilds, requiring local studies. Conflicting results have been reported for clothing's effect on decomposition from various international habitats, with no data for Cape Town, South Africa, despite most local forensic cases involving single clothed decedents. Most taphonomic research uses large samples of unclothed human/animal remains to increase statistical reliability, despite this design not simulating common forensic scenarios. This study examined the effect of seasonally appropriate clothing and carrion biomass load on decomposition and scavenging in the thicketed Cape Flats Dune Strandveld, a forensically significant local habitat. Clothing was identified from forensic case files and tailored to ensure an appropriate fit, preventing unrealistic scavenger access. The decay of ten ~60 kg porcine carcasses, as proxies for human decomposition, was quantitatively examined using daily weight loss. This occurred over two consecutive summers and winters between 2018 and 2020, initially comparing clothed versus unclothed carcasses, then examining single clothed carcasses to ascertain the effect of carrion biomass load. On average, double-layer coolweather clothing notably delayed decomposition in winter, but single-layer warm-weather clothing had a comparatively negligible impact in summer. Weight loss correlated with scavenging activity by the Cape grey mongoose (Galerella pulverulenta), which displaced clothing to feed on the abdomen, more so during winter. Scavenging was hindered by the denim trousers, altering feeding patterns and causing preferential scavenging on unclothed carcasses. Single carcasses received more, longer mongoose visits and decomposed quicker than multi-carcass deployments. These results suggest that clothing delays decomposition locally by modulating the effect of seasonal weather and scavenging behaviour. Additionally, research forgoing forensic realism, with large unclothed samples deployed simultaneously, will inadvertently alter the decay rate, creating inaccurate decomposition models for postmortem interval estimation. Future studies should balance statistical robusticity and forensic realism, especially in environments where scavenging is prevalent. Single carcasses clothed in forensically realistic season-specific appropriately tailored clothing should be considered with statistical replication obtained via temporally separated repeat deployments.
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    The effect of clothing on decomposition and scavenging in two forensically significant habitats in Cape Town, South Africa
    (2024) Adams, Kara Sierra; Gibbon, Victoria
    In South Africa, identifying unknown human remains presents an ongoing challenge given the high murder rate in the country. A crucial aspect of the forensic death investigation involves estimating the postmortem interval, which is influenced by biogeographic factors specific to the region. To ensure the collection of forensically relevant data, the experimental design incorporated single, clothed individuals, as they constitute the majority of unidentified human remains in the Western Cape province. The effect of clothing on scavenging and decomposition were examined in two forensically significant habitats in Cape Town, South Africa. To explore the impact of clothing on scavenging and decomposition, research was conducted in two open habitats, one periurban habitat and one suburban habitat. Six clothed and uncaged porcine carcasses weighing 60kg each were deployed between July 2021 and January 2023 (FHS SEC REF 018_023 & 022_001). Data were collected on carcass mass loss over time, vertebrate scavenger activity, prevailing weather, and carcass tissue desiccation. A comparative sample of 16 unclothed carcasses deployed between 2014 and 2016 was analysed to assess the impact of clothing and biomass load on the decomposition rate. Overall, winter-season clothing delayed decomposition, but summer-season clothing accelerated the process. Carcass weight loss was directly affected by the scavenging of the Cape grey mongoose (Galerella pulverulenta), which accelerated the decomposition rate. Additionally, single carcasses within the same habitat decomposed quicker than the multi-carcass deployments. Natural precocious mummification is a unique phenomenon documented in the Western Cape province, and a novel component of this research was that it formed the first quantitative assessment of desiccation leading to precocious mummification. Printed computing boards inserted into the carcass tissue recorded full-thickness tissue moisture content from three sites on each carcass in 15-minute intervals. The data were analysed through generalised additive modelling with environmental temperature, humidity, solar radiation, and precipitation as covariates. Desiccation in summer appeared to follow an exponential decline, and temperature was the most influential environmental factor. These novel data demonstrate the potential of utilising accumulated degree days and moisture content to estimate the postmortem interval. The combined results advocate using single-clothed carcasses deployed across multiple seasonal trials in forensically significant locations to produce data that can be considered forensically realistic.