Human bony labyrinth is an indicator of population history and dispersal from Africa

Abstract

SignificanceThe cavity system of the inner ear—the so-called bony labyrinth—houses the senses of balance and hearing. This structure is embedded in dense petrous bone, fully formed by birth and generally well preserved in human skeletal remains, thus providing a rich source of morphological information about past populations. Here we show that labyrinthine morphology tracks genetic distances and geography in an isolation-by-distance model with dispersal from Africa. Because petrous bones have become prime targets of ancient DNA recovery, we propose that all destructive studies first acquire high-resolution 3D computed-tomography data prior to any invasive sampling. Such data will constitute an important archive of morphological variation in past and present populations, and will permit individual-based genotype–phenotype comparisons.

Use ancient remains more wisely

“…Last year, a team looking at the morphology of the inner ear noted that researchers were breaking open bony labyrinths and drilling into hundreds of petrous bones for DNA without first taking photographs, or using scanning techniques such as micro computed tomography (microCT) to make morphological records 9 .…”

To curate the molecular past, museums need a carefully considered set of best practices

“…It is important to consider that one residue or substrate can be subjected to several different techniques to address very different questions. The petrous bone, for instance, has become the preferred sampling site for paleogenomic studies of ancient population history because of optimal preservation of endogenous, organismal DNA (10), but the bone can also be useful for stable isotope analysis as a supplement or proxy for teeth in reconstructing diet during early life (11), and it carries important morphological signals of population histories (12). If the entire inner ear is used for DNA extraction, this information is lost, and if sampling involves removal of a large part of the petrous bone, morphological information about sex and childhood disease may be lost as well (13).…”

A Minimally Destructive Protocol for DNA Extraction from Ancient Teeth

“…However, accessing this optimal source of ancient DNA results in the destruction of the inner ear morphology, which is a valuable source of morphological information (de León et al 2018). While there are protocols that reduce the destructive nature of sampling, by sampling from the ossicles of the inner ear (Sirak et al 2020) or performing targeted drilling of the cochlea through the cranial base of complete or reconstructed crania (Sirak et al 2017), some destruction (including that of morphologically-informative inner ear components) is inevitable.…”