Human Male Superiority in Olfactory Sensitivity to the Sperm Attracting Odorant Bourgeonal

Abstract: The present study aimed at assessing possible gender differences in human olfactory detection thresholds for three odorants; bourgeonal, an aromatic aldehyde, helional, a structural analogue of bourgeonal,  and n-pentyl acetate, an aliphatic ester. A total of 500 subjects, 250 males and 250 females between 18 and 40 years of age, were tested using a triangular forced choice method with an ascending staircase procedure. The subjects were asked to sniff the contents of three bottles and to identify the one containing the stimulus presented at a given concentration. Males were found to have a significantly lower olfactory detection threshold for bourgeonal compared to females (3.4·1011 molecules·cm-3 air and 5.9·1011 molecules·cm-3 air, respectively) whereas no significant gender difference in the olfactory detection thresholds for helional (1.4·1013 molecules cm-3 air and  1.3·1013 molecules·cm-3 air, respectively) or n-pentyl acetate (1.4·1014 molecules·cm-3 air and  1.1·1014 molecules·cm-3 air , respectively) were found. This is the first study ever to report a human male superiority in olfactory sensitivity for a monomolecular odorant. One possible explanation for this finding is that bourgeonal may differ in its biological significance for males and females. It has recently been demonstrated that bourgeonal elicits chemotaxis in human sperm cells and olfactory receptors activated by bourgeonal might thus be subject to sexual selection.