Major histocompatibility complex (MHC) social signalling has been found in over
20 vertebrate species so far and is ‘likely the basis for a vertebrate-wide chemosensory
communication system’ [1]. Numerous further examples of MHC social
signalling have been published since Ruff et al.’s [1] exhaustive review, both
demonstrating female reactions to MHC sharing with males (e.g. [2,3]) and
male reactions to MHC sharing with females (e.g. [4–7]). When concentrating
on experimental studies in humans, 15 papers so far claimed to provide evidence
for MHC-linked odours and/or odour preferences (electronic supplementary
material, table S1), and a recent meta-analysis concluded thatMHC-linked preferences
are ‘likely conserved across primates’ [8]. Well-worked-out cases of absent
MHC social signalling would therefore be interesting exceptions of what seems to
be a general rule, and it is important to find and document such exceptions
to learn more about the principles of social signalling. However, easy as it is to
miss an existing effect (e.g. because of problematic experimental protocols or
low statistical power), it is just as challenging to demonstrate that an effect does
not exist.
Probst et al. [9] argue that ...