A post on kissing by fellow SciBling Sheril caught my eye, and I figured, why not pick a friendly argument as my inaugural post at Pure Pedantry (sorry, Jake).
She pointed out a recent SciAm writeup summarizing work by a team of kiss-intrigued researchers, including psychologist Gordon Gallup, PhD, of SUNY, and quips:
"You see, kissing undoubtedly allows us to find out all sorts of information about our partner. We're exchanging pheromones. In fact, when we're engaged, our bodies release a cocktail of chemicals related to social bonding, stress level, motivation, and sexual stimulation. We become, in effect, 'under the influence.' It's powerful."
But I gotta disagree.
As far as humans go, I think that we can pretty much rule out a role for pheromones playing any sort of substantial modulatory role at all. If they do, it's minor and quickly overwhelmed by loads of other factors.
Pheromones undoubtedly play a pivotal role in the attractiveness, solicitations, and mating behaviors performed by most small mammals (think rats, ferrets), amphibians (newts, salamanders), and other crawly little things. In fact, pheromones can be so overwhelmingly powerful to these little critters, the male doesn't even have to be present - sponges soaked in miniscule amounts of sodefrin, a pheromone emitted by male red-bellied newts, attracted female newts from across the pond.
Through studies like this, pheromones have been defined as tiny little chemicals that travel through air or water to affect the physiology and/or behavior of another animal. In essence, they're chemosignals sent by one animal and received by another.
While signals can be sent that (typically sounding something like "mate with me! mate with me!"), who is doing the receiving?
Just about anyone with a vomeronasal organ, as it turns out. Ever seen a deer exhibit a flehmen response? You know, when a male buck will stretch out his neck and peel back his upper lip? Think Mr. Ed, the talking horse. Turns out that you're not seeing the actual magic - when the male assumes this posture, he flattens his tongue against the roof of his mouth to press the pheromonal signals into his vomeronasal organ. Most ungulates, carnivores, even rodents do it...but if you see your date doing it across your candlelit dinner table, I'd make a break for it.
But humans don't have vomeronasal organs at all. They've been relegated to our little group of vestigial organs, right alongside our appendix.
To be fair, we've recently learned that pheromones may also act through the main olfactory epithelium, which we humans most certainly do have - fully functional, intact, and raring to go. So, humans can't be labeled as incapable of receiving these chemosignals.
Now we're getting to the good stuff.
First of all, there are very few papers assessing the role of pheromones in humans. Period. But one of the most seminal studies on pheromones in humans - performed in 1971 by McClintock - is an intriguing example to talk about, as it's still hotly contested.
McClintock and others found that women who lived together on college campuses (i.e. shared a dorm) started cycling together, a phenomenon known as menstrual synchrony. They theorized that pheromones released by the women helped to coordinate the synchronization of their periods; such synchrony is also seen in primates and other social species that live in close proximity, and it's considered to give all females a competitive advantage in the mating world - if you are fertile in the same window that everyone else is fertile, you won't be missing out on any opportunities for male attention. Or so they thought.
But numerous follow-up studies have failed to replicate this synchrony. Mass media and college-aged girls alike latched onto the idea and it stuck, but scientists are still divided. Personally? I certainly don't doubt that humans release pheromones that affect others and that humans may still be responsive to pheromones released by others.
I'm just skeptical of what other factors might be influencing the results.
A while back, researchers revealed a link between the menstrual status of a female lapdancer and the amount of tips that she receives, with dancers earning the most during their peak fertility. They posit that one explanation might be that males that receive a lapdance (and thus doing the tipping) were subconsciously aware of the females' fertility through pheromones that she was releasing upon "close contact."
The idea is intriguing and the speculation warranted. But whether you flip back to the description of what constitutes a "gentleman's club" in the Methods section of the paper (which, by the way, is really endearing; read it for a good chuckle) or go off of your own personal experience (ahem), I imagine that you'll note the 1. noise, 2. smells, particularly if club-goers are smoking and/or drinking, 3. surrounding people and their attitudes and influences, and 4. movements of the dancer herself (which are also associated with cyclicity and hormone levels) would all trump the role of those puny little pheromones. Thoughts?
So, how exactly do menstrual synchrony and lapdancing relate to the role of pheromones in kissing? Think about all of the other factors - which, I might add, Sheril certainly did justice to - that contribute to an encounter, a date, and eventually a kiss. If we are receiving pheromones through saliva that contribute to our feelings of desire and connection with The Other, I don't see how the cultural, psychological, societal, and emotional aspects leading up to a kiss wouldn't completely squelch the already contentious role of the pheromones flying around in that kiss.
Or perhaps I need a bit more hopeless romantic in me :)
Any female who works in a small office where the women's bathroom has a tampon/kotex dispenser has evidence that the synchronized cyle thing is true. There's one week a month when it runs out. And not because that's the week they refill it.
Should be fairly easy to design an experiment.
Hi Kate! Admittedly I'm still not sure why we humans kiss, although I'm glad we do. I also hope you'll check out my post coming tomorrow because I'll be interested to hear your perspective on that one. It's great we're interested in similar subjects and more importantly, I'm so glad you've joined us here on Science Blogs!
There's a big difference between saying that humans don't have vomeronasal at all versus that they're vestigial. But going slightly further along those lines: While it's clear that pheromones no longer serve our species as a receptivity signal over longer distance, that does not preclude the persistence of other functions that operate better at close range. (Apologies in advance, this runs a bit long...)
In particular, I'm thinking about selectivity that optimizes immune function. I wish I could find the paper I read on this -- you have probably seen it yourself, may have even linked to it -- but the gist was an examination of preference for mates with a larger difference in set of disease resistances.
Brief aside: I don't remember whether it tied into the study on women's preferences for shirts previously worn by family-member versus non-family males, and shift of those preferences over the course of the menstrual cycle. IIRC, the authors' conclusions were more along sociological lines, but I could see such a purely biological function figuring into the preference.
Back to the long- and short-range differentiation. Some mating signals have value at either or both ranges. Consider male displays of suitability ("puffery") and, more specifically, within a group setting. Neither of these are specific to humans, but certainly apply. Behavioral displays are typically visual in nature, which has two keys implications. First, it makes them effective at a distance, thus often serving as the initial volley in the mating dance. Second, these displays in some cases can be indiscriminate with regards to target; IOW, undirected advertising to multiple targets potentially may get a better result than directing at a single target.
For the same reasons as behavioral displays, pheromones functioning as a receptivity signal have value at any range. This use of pheromones by humans, however, is vestigial at best, as you say.
On the other hand, the immune selectivity function is very much specific to the individual. But because the overall utility of the pheromone mechanism has led to a weaker receptor system, the emitter needs to "boost their signal". (I mean this metaphorically) That means either increasing their output or... getting closer to the receptors. And so here's a theory: Kissing may simply be a by-product of getting literally in the face of a potential mate.
As for the 10% of the world's people that don't kiss: They're still nuzzling or breathing on each other's faces, which would go toward the same purpose. Aside from the far-from-insubstantial implication of cultural dictates for or against the practice, lip-lock is functionally a double-edged sword and so not an automatic win: It's an effective "docking mechanism", but it also an effective way to transmit communicable disease. Are those non-kissing cultures in areas where (ahem) swapping spit is a greater vector for disease?
I'm totally shooting from the hip on this, so if you've seen any further research along these lines, please to post it!