You must have lived under a rock for the last 50 years if you haven’t heard about those chemical text messages called pheromones. Just look around you. No, truly observe. Dogs can’t resist the urge to mark their territory as they patrol the neighborhood. Laboratory mice cower in the corner of their cages when exposed to the smell of cat urine. And, we all know about those pesky mosquitoes drawn to your breath CO2 and body heat.
What we can learn about pheromones from Drosophila
Here is something puzzling and instructive at the same time. The male Drosophila fruit fly emits a volatile substance called CVA (11-cis-vaccenyl acetate) which works its magic on the female fly and makes her enthusiastically submit to his advances. But whatever residue of the aphrodisiac lingers on her body turns off an approaching male and he beats a hasty retreat. It’s the same chemical substance but it has opposite effect. From a natural selection point of view, it makes perfect sense. The impregnated female and the horny male don’t need to waste energy on pointless sex.
Is there a human sex pheromone?
In short, the behavior of everything around us is controlled by a symphony of odors. So is it any wonder that investigators have been on the hunt for the elusive human pheromone for the past 50 years? Just Google “human pheromones” and you’d get hundreds of thousands of hits.
Why this intense interest? Because there is money in it. Just go to the perfumes section of any department store and you’ll see the chemical warfare arsenal designed to lure you (if you are a male). Or check out the man-toiletries area of the store where products are hoping females will be captivated by the musk scents of the after-shave lotions. But, does it really work?
Pheromones will improve your sex life, a common sales pitch goes. But despite decades of research and untold millions of dollars, not one chemical has been identified that causes the release of a behavioral pattern. Which brings us to a bit more sophisticated understanding of pheromone effects.
The pheromone hitting the female fruit fly’s antennae caused the release of her receptive behavior; nothing romantic, nothing volitional. It’s all automatic and hard-wired. This type of behavior is uncommon in mammalians. More common are priming effects, in which the physiology of the recipient of the pheromone is changed, without immediate behavioral changes. For this kind of effect, evidence does exist.
We’ve lost our pheromone sense
In a study of menstrual cycle synchronization, a team led by Martha McClintock at the University of Chicago, collected body secretions from women at different times in their menstrual cycles and presented the substance under subjects’ noses. The test subjects either accelerated or slowed their cycles to synchronize with the donors’, even without conscious perception of the odor. However, more recent studies challenge this study, and the phenomenon of menstrual synchronization is disputed, even when women are living together.
The whole idea of human pheromones becomes even more problematic because the machinery that mediates pheromone effects on the brain of Drosophila and mice is barely present in humans. In non-humans, the organ that senses the pheromones is called the VNO (Vomernasal organ), which in humans is vestigial. Which raises the question: Why would natural selection allow the loss of such an important organ?
The answer is quite fascinating. Recent research showed that at about the same time our primate ancestors gained color vision, they also lost the genes for the VNO receptors. In other words, we switched from experiencing the world through a bouquet of odors wafting up our noses to the symphony of colors imprinted on our retinas.
Which is better? I suspect if you asked fruit flies, they would tell you they are quite happy, thank you. For myself, I am very happy to watch a beautiful young woman playing tennis, sans her armpit smell.