Several ancient cultures attributed erotic properties to certain fruits and vegetables. Take the tomato. In Hebrew, its name translates to “the seductress”. South American Indian cultures concurred in the belief that several other plants of the Solanaceae (the nightshade family) are indeed erotic. Is it the color? Probably not.
More likely it is the alkaloids, a powerful group of compounds that has strong psychogenic, sometimes hallucinatory, even toxic, properties that put the erotic in the term erotic food. Nicotine, opium, cocaine, psilocybin (if you don’t know what psilocybin is, think “shrooms”, or magic mushrooms), and the pre-teens favorite ephedrine are all alkaloids.
And my favorite veggie (actually a fruit), the eggplant, belongs to this hallowed family as well. I have yet to find somebody who doesn’t like it, cooked in one form or another. I have to admit that the smell of freshly-ground coffee (caffeine is an alkaloid) makes me feel happy but erotic? That’s carrying it a bit too far.
Drosophila and rotten veggies and fruits
Fruit flies (Drosophila melanogaster), like males and females of many animal species, produce chemical compounds that they use to find each other and to communicate their mating status. These volatile pheromones diffuse, and putative mating partners can detect them over fairly long distances. Female moths, for instance, release sex pheromones that can attract males from several miles away. A series of cues from the female Drosophila, including a pheromone bouquet spread on her abdomen, elicit sexual arousal in the male fly.
Yael Grosjean and her coworkers of the University of Lausanne, Switzerland, discovered that odors unrelated to the female also promote male courtship behavior. They show that phenylacetic acid and phenylacetaldehyde—two aromatic compounds found in fruits and other plants—specifically activate an olfactory (smell) receptor in sensory neurons on the fly nose (the antennae), thereby triggering male courtship behavior.
But wait, didn’t we just say that the female has pheromones on her abdomen that trigger sexual behavior in the male? Yes. But apparently, it’s not enough. Odors emanating from the deliciously rotten fruit play a role as well.
In other words, the male is getting chemical cues from multiple sources. How various sensory signals coming from different sources are integrated and computed in the brain into an actual decision is poorly understood. It seems, however, that the neurons conveying food or female-related odors connect to a unique center that determines whether the olfactory environment is amenable to courtship. How this neural circuit reaches ‘decisions’ and how it triggers behaviors is still unknown.
But why, you might wonder, should food odor become a sexual cue in fruit flies? First, just think of us humans. Where do we find potential mates? In the bar, at a party, for the most refined among us—in a museum or the opera. The chance of boy meeting girl is simply better where we congregate. But there is a more subtle reason for meeting at the garbage dump: That’s how the male can exert influence where his female lays her eggs.
If the odor of phenylacetic acid is strong, it signifies lots of food for the hatchlings—better chance for his DNA to survive and be passed on. If the odor is faint, it means low food supply. Then the male fruit fly may decide that although the female’s belly pheromones make her pretty attractive, that’s not quite enough. He may try his luck at a smellier party. So what it boils down to is control: The male seeks control of his female. Is there no Gloria Steinem-equivalent of female flies?
What does it have to do with us?
Evolution is conservative (in a non-political sense); nothing is wasted, everything conserved. What arouses a male fruit fly still has an effect on us. Cosmetics manufacturers trumpet the role of pheromones in their products. And why not? Who among us doesn’t want to be sexually attractive? Problem is, most of the advertising claims are patently false. But, it is nonetheless remarkable that the very chemical compounds phenylacetic acid and phenyl acetaldehyde that give the male fruit fly an irresistible sexual appetite are also pleasant to humans and are used in perfumes for their sweet, floral smell.
It remains to be seen to what extent environmental stimuli affect sexual behaviors in other species, including humans. Is a silky transparent nightgown one of those environmental stimuli? Or a low “bedroom voice”? I would think Hollywood movies should be a rich source of investigation of such sexual cues.