Sniffer dogs are being used in a wide variety of roles in the modern world. These roles range from conservation efforts that find endangered species, to drugs and contraband, to search and rescue, and even diseases like COVID-19.
Dogs fill these roles well because of their extraordinary sense of smell, but their abilities in this regard are so profound that even now we are struggling to measure dog's sense of smell limitations. To provide some context, your sense of smell works by specialised smell neurons detecting particular "smelly" chemicals, then sending that information to other parts of the brain. Broadly speaking, the more smell neurons you have, the better sense of smell you will have with regards to sensitivity and the number of smells you can detect.
Humans are somewhere in the middle of the pack when it comes to our sense of smell abilities; we have about five million smell neurons, which contributes to our ability to distinguish around one trillion distinct odours. It sounds impressive, and for most non-mammalian creatures, it is, but this is paltry compared to dogs which have somewhere in the region of 200 million smell neurons.
Currently we do not know how many distinct smells a dog can detect, and some researchers suggest that there is no practical limit. Dogs have further advantages for their sense of smell compared to humans; about 6 per cent of their DNA is devoted to odour compared to 2 per cent in humans. Muscles in their nose ensure than specific smells reach specific smell neurons.
There's further pitfalls when it comes to understanding dogs and their sense of smell. It might be tempting for us to look at our own sense of smell, compare that that data to parts of our DNA that codes for smell detection and use that information to extrapolate sense of smell abilities for dogs much in the same way mice have done for humans.
However the part of the DNA dogs have for their sense of smell is markedly different from humans, meaning we will have to be very careful when trying to make meaningful comparisons. Also, variation of these sense of smell genes in dogs is exceptionally high, and we don't yet know what this means for their abilities. It could mean that olfactory information is translated and interpreted in an entirely different way for dogs, and this makes assessing their abilities in the laboratory even more challenging.
So with all this in mind, just how powerful is a dog's nose? Research has suggested that dogs can smell odorants in the parts-per-trillion range, or even parts-per-quadrillion. Careful testing and exploration of dog's olfactory abilities will help to improve the outcomes for dogs with jobs.
Response from: Dr. James Hayes, Research Fellow, School of Civil and Environmental Engineering, UNSW
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