You may notice that dogs are constantly sniffing – the ground, your food, another dog’s butt. We’ve grown accustomed to these kinds of behaviors from our furry friends. But, as humans, we would never go up to a stranger and take a few whiffs.
Dogs have evolved an acute sense of smell, relying heavily on this sense to survive and interact with their environment. This is in large part due to their physiology and their olfactory organs in particular. Canines possess more than 1,000 olfactory receptor genes and more than 200 million olfactory receptors in the nose. Humans, on the other hand, have about 400 identified receptor genes and only about five million receptors. But despite these physical limitations, our brain is highly complex, and a growing body of literature suggests that olfactory processing continues to play an important role in human behavior.
So, if dogs and other animals use their nose to sniff out their social environment, what about humans? A recent study (Frumin et. al.) proposed that handshaking might actually serve a social chemosignaling purpose. While speculative, the authors suggest that humans actively seek chemical signals from social interactions and may use this information to drive behavior. This experiment was set into motion after the researchers noticed that humans often sniff their own hands after shaking the hand of another. To examine this behavior experimentally, they secretly filmed 271 people during a “greeting” and found that the subjects significantly increased sniffing of the hand used to shake.
The Frumin study joins a host of other experiments that have sought to explore the role of human social chemosignals. A famous 1971 study found that co-habiting women developed synchronized menstrual cycles, proposed to be in part a result of pheromone secretion. A second study found that women preferred the smell of t-shirts belonging to men who had an immune system complex most dissimilar from their own. While the exact results and mechanisms for these studies remain to be tested, it is likely that odors, whether conscious or unconscious, can play a significant role in behavior.
Researchers are still trying to learn more about the role of olfaction in human behavior, and in particular, the role of subliminal chemosignals proves difficult to study. However, as the field of human olfaction grows, we will continue to learn more about the olfactory capabilities we share with other animals.