The Science Of Tissue Depth Libraries
One of the technical foundations of the Punín-2 reconstruction — the “libraries of data to determine the right thickness of tissues in particular places” that Rynn used — is worth explaining in more detail, because it illustrates both the scientific grounding and the inherent approximation involved in forensic reconstruction.
Tissue depth data for forensic facial reconstruction comes from studies that measure the distance between the bone surface of the skull and the surface of the skin at specific landmark points on the face. These measurements have been collected using multiple methods: ultrasound measurement in living subjects, caliper measurement at dissection of cadavers, and increasingly using medical imaging (CT scans, MRI) that can map the soft tissue profile of the face simultaneously with the underlying bone.
The measurements from these studies are compiled into tables that give average tissue depths at each landmark point, broken down by variables that affect the values: sex (because males and females have different average fat distributions and muscle volumes), age (because tissue depths change with age, particularly with weight changes and the changes of aging), and body mass index (because heavier individuals have more subcutaneous fat, which increases tissue depths).
For ancient individuals, the application of these tables involves judgment about which reference population is most appropriate. For the Punín-2 man — a Native American male in his fifties — the appropriate reference data would ideally come from measurements of Native American males of similar age. The degree to which the available tissue depth data represents this specific population affects the accuracy of the reconstruction.
The tissue depth libraries that exist for Native American populations are less comprehensive than those for European populations, which have been the subject of the most extensive data collection efforts. Research programs that have expanded the tissue depth data for under-represented populations have improved the accuracy of reconstructions from those populations over time, but the data gaps are not fully closed.
This is one reason why local consultation — the kind that Rynn undertook with people of the Chimborazo region — is valuable as a complement to the tissue depth data. The living descendants of the ancient individual represent a population that is more directly relevant to the reconstruction than any generic tissue depth table, and their feedback about whether the reconstruction “looks right” is a form of calibration that the data tables alone cannot provide.