The auditory section of the inner ear, or the "cochlea," does not have the same shape from birth depending on whether one is a man or a woman. This is due to the torsion of the cochlear spiral, which differs based on gender, especially at its tip.

Demonstrated by a group of scientists, these results have helped develop the first reliable method for sex determination, including among children and cases where DNA is missing or too altered. Until now, it was impossible to determine the sex of a child from its skeleton, while for adults this could be done reliably only from studying the pelvis, which is not always preserved.

The authors observed 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 the study allows sex assessment from the human skeleton with a mean accuracy ranging from 0.91 to 0.93 throughout life.

Since the cochlea is among the hardest bones in the skull--a bone that is found very frequently at archaeological sites--this technique can determine the sex of very old fossils, even when fragmentary or immature. This research was featured in an article published by Scientific Reports.

https://www.cnrs.fr/en/inner-depths-ear-shape-cochlea-indicator-sex

https://www.nature.com/articles/s41598-019-47433-9

http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Fcochlear-shape-reveals&filter=22