Validating the probabilistic sex diagnosis (DSP) method with a special test case on Pre-Columbian mummies (including the famous Rascar Capac)

Many museums have either one or more mummies in their collections. The Royal Museums of Art and History in Brussels is no exception and houses several Pre-Columbian mummies, including the one that inspired Hergé, author of the Tintin comics, to create the character of ‘Rascar Capac’. The accurate identification of the sex of a particular mummy is important for testing hypotheses about social structures in ancient societies. Sexing of mummies is mostly based on visual analysis from CT and MRI scans and macroscopic examination from the skeletal tissue such as genitalia and breasts, although skeletal tissue is not always well preserved. Probabilistic Sex Diagnosis (DSP: Diagnose Sexuelle Probabiliste) is a sex estimation method which has recently proved to be highly effective on different modern human and ancient European populations. The aim of this study was to see if it was possible to apply and validate virtual DSP on a study of four ancient Pre-Columbian mummies from South America (which are outside the reference population of DSP). Virtual DSP was performed in the software ‘lhpFusionBox’. All mummies were CT scanned, 3D models were created and virtual DSP was performed. Sex was determined with a probability of 99.9% or over in all cases (DSP determined one male and three females). Preserved skeletal tissue remains confirmed DSP results in half of the mummies. A Principal Components Analysis (PCA) was performed on the DSP results of the mummies and a modern human (MH) population. Half of the mummies were outside the 95% range of the DSP values of MH, largely due to their smaller size. When size was accounted for, they were within the MH range. The unknown sex mummies identified as females by DSP were found to be grouped with the known sex female mummy and the MH females. Similarly, the unknown sex mummy identified as male by DSP was also found to be grouped with MH males. The use of PCA analysis on DSP results is an effective tool to validate DSP results, even with individuals outside of the reference population. Despite differences in size from ancient to modern humans, DSP was found to be accurate and can be used with mummies and other ancient populations from different countries around the world.