Smelling Healthy

My dog isn’t much of a retriever. He isn’t particularly interested in fetching a ball or Frisbee. There is one exception to the rule, however. If we’re in the woods, he’ll gladly bring back a stick that I throw deep into the woods. What’s interesting is the way he finds it. He doesn’t appear to watch where the stick lands, as I do. Instead, he tries to find the trail of scent the stick left as it flew through the air. On the down side, it often takes him awhile to find the stick. On the upshot, he’d be no worse off if we played the game at night, when my eyesight would largely fail me. In that respect, his nose is less efficient but more reliable than my eyes.

The human eye is very sensitive. We have about 125 million receptors on the retina. The great majority of these receptors (120 million) are called rods, which allow you to distinguish between shades of grey in low light. The remaining receptors (5 million) are called cones, which allow perception of color in bright light. A dog’s eye is generally less sensitive. While a normal human’s vision is said to be 20/20, a normal dog’s vision is 20/75, which is to say that a dog would have to be 20 feet away to see the same object that a human could see from 75 feet away. Also, a dog has relatively poor color vision. Their biggest problem, it would appear, is the fact that they’re only two feet tall. If you were two feet tall and relied exclusively on sensory data from your eyes, you can imagine how much you’d miss.

As sensitive as the human eye is, a dog’s nose is even more sensitive. Compared to the 125 million receptors in the human eye, a dog’s nose carries over 200 million receptors. The human nose, in contrast, only has about 5 million receptors, some of which are re-dedicated for taste and temperature – think of the “smell” of menthol or wine. Basically, what I’m trying to get at is that humans smell badly, and men smell worse than women.

This is why I found it particularly troubling to hear that olfaction may play a large factor in mate selection. The other day a friend mentioned a study she had read a few days prior. The gist of the study was that a group of men were asked to wear a t-shirt to bed for a couple of nights. These shirts were taken, placed in marked bags, and given to single women to rate in terms of their pleasantness. Their responses were recorded. Some days later, the men and women were brought together for a party and the women were asked to rate the men in terms of attractiveness. Women tended to give high ratings of attractiveness to the same men whose t-shirts they found pleasant-smelling days earlier. (Unfortunately, I was not able to find this study anywhere, so I cannot provide a link.)

In another study, it was suggested that women are particularly sensitive to the smell associated with the molecule that enables the immune system to recognize foreign bodies (MHC – major histocompatibility complex). Women tend to prefer the smell of men that are immunologically similar to their biological fathers. This makes evolutionary sense. You’d want your kids to be able to combat the same antigens as you, because they are likely to be in the same environment. However, given the choice between immunologically similar and immunologically identical, women prefer similar. This may be a check against the ills of inbreeding. Interestingly, women do not prefer the smell of men that have antibodies similar to their mother nor to their non-biological father, in the case of adoption or re-marriage. The preference, it appears, is not about familiarity, but biology. Indeed, most women are unable to identify preferred smells as being familiar, nor are they more likely to correctly identify these smells as being of human origin, as distinguished from other household smells.

After encountering these studies, I can’t help but ask: if so much is riding on the way we smell, then how come we’re so bad at smelling? Would there be less divorce if we had 200 million olfactory receptors, instead of our paltry 5 million? Do people with more acute senses of smell stay together longer? Is using axe body spray going to screw up your kid’s chances of leading a long, healthy life? Was love potion number 9 just glorified antibiotics? Should personal ads read: SWM seeking SWF with good sense of humor and desire to combat like antigens?

Much like my dog trying to find a stick with his nose, trying to find a husband using your nose may not be the most efficient method, but it may prove to be the most reliable, evolutionarily speaking. We all know that it's quite easy to fool the eye. Language also can be manipulated with ease. Meanwhile, the failure of various pheromone colognes that have hit the market over the years attests to the discernability of the human nose. Maybe cereal box superhero Tucan Sam was dispensing sage relationship advice when he remarked, “Just follow your nose!”