The organ of hearing, sexual marker

L'organe de l'audition, marqueur sexuel

A recent press release from the CNRS (French National Center for Scientific Research) throws a spanner in the works following research carried out jointly by a Franco-South African and interdisciplinary team of scientists from the CNRS (French National Center for Scientific Research), the UT3 Paul Sabatier (University of Toulouse) and the University of Clermont Auvergne, as well as from Johannesburg and Pretoria. The results of the study are consistent for all these teams.

The cochlea, the snail-shaped organ of hearing where the hair cells are located and which, stimulated by the liquid in which they are immersed (endolymph), excite the nerve fibers of the auditory nerve, would be different according to sex, and this, from birth.

It is thanks to the use of micro scanners and 3D reconstruction of cochlea sections that we have been able to observe these fundamental differences. Thus, if the shape of the cochlea is oriented in the same way for male and female cochleas, the geometrical differences are clear with a more pinched aspect of the extremities of the first and second cochlea, in men, whatever the age.

Female (left) and male (right) mean shapes of the cochlear spiral on which torsion is color-coded While the 2 shapes are oriented in the same way, the geometric differences are clearly visible here © C. Samir, A. Fradi, and J. Braga


What applications can we draw from these elements ?

First, and anecdotally, it seemed logical that the South African studies should also look for a difference in the shape of the cochlea according to ethnic origin. This difference turned out to be non-systematic, although it is known that human skulls, according to their shape, can be classified as mongoloid, negroid and Caucasian.

On the other hand, whatever the origin of the cochleae, all showed a significant difference according to sex.
The number of cochleae studied in France was 32 for women and 22 for men.
In South Africa, the figures were 18 women and 22 men.
The method developed by the researchers gives an accuracy rate between 0.91 and 0.93, which is excellent.

The identification of a skeleton and in particular its sex, can be done in different ways :
• By DNA, if the bone is analyzable and therefore if the skeleton is not too old ;
• By the study of its pelvis, wider in women, with the same restrictions (because the pelvis destroys quickly).

When the skeleton is older and, in particular, during archaeological excavations, the two previous identifications are generally impossible. The sex, to this day, was therefore not identifiable.
Indeed, the search for DNA is very difficult when there is only bone debris.
The same is true for the pelvis, which is often destroyed in women and is of similar size for both sexes before adolescence.

But the cochlea, on the other hand, is a very hard bone and one of those most frequently found during archaeological excavations.
It is therefore now possible, thanks to this Franco-South African work, to attribute a sex to a large number of skeletons kept in museums.

Moreover, this form of cochlea specific to men and women would explain why women perceive high frequencies better than men . Perhaps this would also explain a lesser damage with the years in the female sex on these high frequencies.

To date, no scientific explanation is advanced to explain these anatomical differences.


Sources :

In the hollow of the ear: the shape of the cochlea is a sexual marker
Press release, August 5, 2019.

J. Braga and al
Cochlear shape reveals that the human organ of hearing is sex-typed from birth-
Nature, Scientific reports 9, article number 10889 (July 2019)


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