Time for some smelly science
Fresh Air’s Terry Gross interviews Alexandra Horowitz to discuss her new book, Being a Dog. One of the fascinating capabilities that Alexandra mentions in the interview is that dogs can tell time via smell. We know dogs have a tremendously more sensitive sense of smell compared to us. It makes sense that dogs can use smell to tell time, if you think of time in a different way. For example, they can smell just traces of something left behind by another animal. Therefore they know that a faint smell is from the past. They also can detect faint smells in the air, perhaps around the corner. Therefore, they can smell the future. The way Alexandra describes a more traditional sense of time is pretty interesting. As the air heats up in your house, you can imagine air currents change. The smell of the room should change too. Remember we are visual creatures but dogs are more olfactory. Imagine 3D smell instead of sight. It makes sense that the scent profile of a room would change depending on the time a day and therefore a clue to what time it is. It’s very much like how we can use shadows to guess if it’s midday or evening.
Alexandra mentioned the vomernasal organ, sometimes called the Jacobson’s organ and I’m guessing a lot of people have never heard of it. The vomernasal organ (VNO) is the peripheral sensory organ in the olfactory system that involves chemoreception. Pheromones are often mentioned in the definition of VNO but in some non-mammalian species, such as snakes, VNO might be used to track prey using chemoreception. Therefore focusing just on pheromones is not broad enough of a definition. There is some debate as to whether or not humans have a VNO. It seems clear that it exists in the embryonic stage. The debate seems to be whether or not it is functional as adults. The article by Meredith (linked below) focuses not on whether it exists but what its function could be.
The other interesting thing from the Meredith article is the section about pheromones, where he talks about the definition and its use in scientific discourse. So first, the definition.
What is a pheromone and is it a well-defined, scientifically useful concept? The term pheromone was coined to describe a chemical substance which carries a message about the physiological or behavioral state of an insect to members of its own species, resulting in ‘a specific reaction, for example a definite behaviour or a developmental process’ (Karlson and Luscher, 1959).
He goes on to discuss how communication by pheromones needs to be mutually beneficial for sender and receiver. That benefit, is in an evolutionary sense.
The term pheromone is not going to disappear so long as it holds the public fascination. Its use for a class of chemicals that communicate information seems reasonable, but the definition is important if the term is to be useful in scientific discourse. Too rigid a definition can make its applicability to real situations so limited that it is useless. We know that even archetypal insect pheromones are not unique chemicals used by single species, as supposed in some definitions [see discussions in Beauchamp et al. and Albone (Beauchamp et al., 1976; Albone, 1984)]. Similarly, too broad a definition devalues the term and also makes it useless.
Getting back to the interview with Alexandra and dogs’ incredible sense of smell, there are some great illustrations in the PBS, NOVA article below. An eye opening estimate of how much more sensitive dogs’ sense of smell compared to ours is something like 10,000 to 100,000 times ours.
In Alexandra’s previous book, Inside of a Dog, she writes that while we might notice if our coffee has had a teaspoon of sugar added to it, a dog could detect a teaspoon of sugar in a million gallons of water, or two Olympic-sized pools worth.
Hopefully you have a sense of dogs’ great sense of smell now.
Human Vomeronasal Organ Function: A Critical Review of Best and Worst Cases
Michael Meredith
Chem. Senses (2001) 26 (4): 433-445.
http://chemse.oxfordjournals.org/content/26/4/433.full
Dogs’ Dazzling Sense of Smell
On NOVA
http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html
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