To cast light on whether friendship causes similarity of scent, or similarity of scent causes friendship, Dr Ravreby, Dr Snitz and Dr Sobel investigated whether e-nose measurements could predict positive interactions between strangers -- the sort of “clicking” that is often the basis of a new friendships.
To this end they gathered another 17 volunteers, gave them t-shirts to wear to collect their body odours, ran those odours past the e-nose, and then asked the participants to play a game.
That game involved silently mirroring another individual’s hand movements.
Participants were paired up at random and their reactions recorded.
After each interaction, they demonstrated how close they felt to their fellow gamer by overlapping two circles (one representing themselves, the other their partner) on a screen.
The more similar the two electronic smell signatures were, the greater the overlap.
Participants also rated the quality of their interaction in the game along 12 subjective dimensions of feelings that define friendship.
Similar odours corresponded to positive ratings for nine of these dimensions.
Intriguingly, however, two participants smelling alike did not mean they were any more accurate at the mirroring game than others, as measured by a hidden camera.
Why scent might play a role in forming friendships remains obscure.
Other qualities correlated with being friends, including age, appearance, education, religion and race, are either immediately obvious or rapidly become so.
But while some individuals have strong and noticeable body odour, many -- at least since the use of soap has become widespread -- do not.
It is present.
But it is subliminal.
Dr Ravreby speculates that there may be “an evolutionary advantage in having friends that are genetically similar to us”.
Body odour is known to be linked with genetic make-up (particularly with the genes underlying part of the immune system called the major histocompatibility complex).
Smelling others may thus allow subconscious inferences about genetic similarity to be drawn.
That still, however, does not quite answer the question.
Dr Ravreby speculates that odour-matching of this sort may be an extended form of kin selection, which spreads an individual’s genes collaterally, by helping the reproduction of relatives who are likely to share them.
If those who smell similar are kin enough for this to apply, their children will be as well.
“So by helping friends,” Dr Ravreby offers, “we help spread our own genes.”