Elephants were shown to have a huge number of olfactory receptor genes, which implies they likely have a huge sense of smell. The olfactory (smell) receptor gene repertoires of 13 placental mammals were compared and, surprisingly, elephants had a very large repertoire. The olfactory gene repertoire in elephants was even larger than in dogs. It is not so surprising that elephants had a larger repertoire than humans, whose sense of smell pales compared to many animals.
The study used a new phylogeny-based, meaning from an evolutionary perspective, method to classify groups of known olfactory genes from 13 placental mammal species. Then the olfactory gene groups were compared and ordered. The numbers of olfactory receptor genes ranged from 1,948 in elephants to 296 in orangutans. The results from the study showed that the number of olfactory receptor genes increased over time while it decreased in primates, in an evolutionary sense. Humans have a measly 396 olfactory receptor genes.
The study was carried out in the Department of Applied Biological Chemistry at the University of Tokyo. Dr. Yoshihito Niimura was the lead author and the study was published in the journal Genome Research.
Olfactory receptors are specialized cells that can capture small molecules that break off from objects in the environment and become airborne. Once the olfactory receptor receives a molecule, it sends signals to other neurons in the olfactory sensory system and that signal information will finally reach the brain. The brain processes information about the molecules that are caught by the olfactory receptors and then creates a smell perception. For example, if there is a rose in the environment some of the rose particles will become airborne. When someone sniffs in the air nearby the rose, these particles will get into the nose and they will be captured by the olfactory receptors. The brain will process the signals and create the sweet smell of the rose.
The olfactory receptors are differentiated during development by certain genes that are activated at a critical developmental point to turn the cell into an olfactory receptor. These genes have been determined for some species of animals and thus they can be compared among different types of animals.
While the study showed that elephants have a large number of olfactory receptor genes, it can only be inferred that they have a resulting expanded sense of smell. There is not enough information yet about how numbers of olfactory receptor genes relate to smell sensitivities and ranges. In order to determine for sure that elephants have an expanded sense of smell, studies that involve observing elephants smelling things would be necessary. Also, designing tests to determine what they smell or do not smell would be required. This would be a daunting task for any animal behavior scientist.
Some studies have been done, however, that have shown elephants have a superior sense of smell. It has been reported that elephants can smell the difference between two different tribes in Kenya. Also, elephants use smell to find food and to identify family members. A complexity that should be noted here is that it is likely that some of these abilities are actually due to the detection of pheromones, which are airborne hormone-like molecules. However, pheromones have been shown to be received by the olfactory system and so it is a related phenomenon. Elephants likely have a huge sense of smell that plays a big role in many of their behaviors.
By Margaret Lutze