It is commonly believed that we have a poor sense of smell relative to other mammals, most notably the dog. However, a review published today reports that, based on 14 years of study of the olfactory system, humans have an excellent ability to discern different odours. We are just sensitive to different scents compared with other mammals.
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In the 19th century the prominent neuroanatomist and anthropologist Paul Broca reported that the ability to perform certain tasks was related to the size of the corresponding region of the brain. Consequently, since the olfactory bulb occupies a relatively small area in the human brain, it was assumed that humans have an inferior sense of smell compared with other species.
John McGann, a neuroscientist at Rutgers University in New Jersey, has been studying the olfactory system for the last 14 years and now reports that humans actually have remarkable olfactory capabilities that have been underestimated for hundreds of years.
For so long people failed to stop and question this claim, even people who study the sense of smell for a living. The fact is the sense of smell is just as good in humans as in other mammals, like rodents and dogs".
McGann reveals that the number of neurons in the olfactory bulb is relatively similar between different species. Despite body weight differences of 5800 fold between some species, the number of olfactory bulb neurons only changes by 28 fold. He also highlights that, in absolute terms the human olfactory bulb is bigger in volume than those in many other mammals. The apparent discrepancy in sense of smell is a consequence of different species being more sensitive to different scents.
For example, humans are more sensitive than dogs at detecting the odour of a compound found in bananas. Similarly, recent research found that humans could readily distinguish two different scents that mice treated as being the same. Like other mammals, humans can distinguish between an incredible number of odours and, if we were to take to all fours, we would be able to follow outdoor scent trails in the same manner as a dog.
It is becoming apparent that we actually use our sense of smell more that we appreciate. Humans subconsciously use scent as a means of communication about familial relationships, stress and anxiety and reproduction status. Smell can also evoke strong emotional and behavioral reactions in humans, such as bringing back memories of events or places experienced in the past.
Although it is clear that our belief that the human sense of smell is impoverished is based on a 19th-century myth, further research is required to fully understand the role and capacity of the human olfactory system.
- American Association for the Advancement of Science. Press release 11 May 2017. Available at https://eurekalert.org/pub_releases/2017-05/aaft-tms050817.php
- McGann JP. Poor human olfaction is a 19th-century myth. Science May 2017;356. Epub ahead of print. Available at http://science.sciencemag.org/content/356/6338/eaam7263