Abstract
Sex differences in behavioral and neural characteristics can be caused by cultural influences but also by sex-based differences in neurophysiological and sensorimotor features. Since signal-response systems influence decision-making, cooperative and collaborative behaviors, the anatomical or physiological bases for any sex-based difference in sensory mechanisms are important to explore. Here, we use uniform scaling and nonparametric representations of the human cochlea, the main organ of hearing that imprints its adult-like morphology within the petrosal bone from birth. We observe a sex-differentiated torsion along the 3D cochlear curve in samples of 94 adults and 22 juvenile skeletons from cross-cultural contexts. The cochlear sexual dimorphism measured in our study allows sex assessment from the human skeleton with a mean accuracy ranging from 0.91 to 0.93 throughout life. We conclude that the human cochlea is sex-typed from an early post-natal age. This, for the first time, allows nondestructive sex determination of juveniles’ skeletal remains in which the biomolecules are too degraded for study but in which the petrosal is preserved, one of the most common bone within archaeological assemblages. Our observed sex-typed cochlear shape from birth is likely associated with complex evolutionary processes in modern humans for reasons not yet fully understood.
Highlights
Signaling within a species influences decision-making, maximizes cooperative and collaborative behaviors involved in sexual or other forms of social selection[1,2]
We first tested the presence of sexual dimorphism in the 3D cochlear shapes in this sample of 94 adults by modeling mathematically the 3D cochlear shape by an open curve located along its outer periphery[20,35]
We reduced the dimensionality of the 3D cochlear shape variables through unsupervised learning and principal component analysis on the tangent space of shapes (TPCA, with the first and the second eigen projections) (Methods)
Summary
Signaling within a species influences decision-making, maximizes cooperative (e.g., sharing, communication) and collaborative (e.g., coordination) behaviors involved in sexual or other forms of social selection[1,2]. Previous studies investigated human sexual dimorphism in cochlear size and gave contradictory results[16,17,18]. This was likely caused by the fact that none of these studies[16,17,18] attempted to measure the allometric effect of the www.nature.com/scientificreports/. We further tested the applicability of our results for sex determination by measuring the accuracy of a method based on our observed sex-differentiated cochlear shapes. Any method for sex determination from the juvenile skeleton should be based on the description of purported sex-differentiated skeletal features but should provide repeatable accuracy
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