I am currently reading an interesting book by Ed Yong, An Immense World: How Animal Senses Reveal the Hidden Realms Around Us. It is about the senses of animals, more precisely, about the organs of these senses and how animals perceive the world. For me, the book is full of intriguing facts and discoveries.
The author starts by noting that every animal has its own “sensory bubble,” Umwelt. This term was introduced by Jakob von Uexküll in 1909. Essentially, it’s exactly how they feel the world around them. We see colors, smell scents, and hear sounds differently than other animals, and this difference isn’t measured just by a simple more-or-less scale, but rather as a complex concept. For example, in 1974, Thomas Nagel released the article “What is it like to be a bat?”. Just imagine how the world around us would look if our sensory organs were replaced with radar, allowing us to see scents and hear the direction of the faintest sounds with precision to the degree.
In the chapter about olfaction, the author describes a dog’s nose. In fact, not only dogs—almost all animals see the world through their noses much more clearly than we do. It turns out that the air inhaled through the nose goes into a separate chamber. A wet nose captures molecules from the air with mucus, which then are sent to this chamber for analysis. When humans breathe, the air is inhaled and exhaled through the same “ventilation” channel. For dogs, for instance, it’s different. Their nostrils can function independently from one another. Inside the nasal cavity, special membranes separate the nasal passage into two distinct channels. The first channel is used for breathing, the second—for the operation of olfactory receptors. Furthermore, dogs exhale not just through their nostrils but through special slits located on the sides. Then the air turns and pushes a new air batch back into the nose. Ultimately, a dog analyzes a continuous stream of air, which it also actively pushes through such a configuration. That is, when a dog exhales, it simultaneously inhales as well. This can continue for up to a minute. Not quite like us.
The “sensors” in the nose are long neurons that look outward from the nose on one end and into a part of the brain called the olfactory bulb on the other. Ours are poorly developed, but in animals with keen olfactory senses, they are much larger, as is the number of these neurons in the epithelium and their diversity.
It turns out that some snakes manage to be undetectable even to animals for whom scent is everything. This applies to the rattlesnake, for example. Dogs, mongooses, and meerkats simply cannot sense it. However, if it sheds its skin, they can smell the skin. Apparently, snakes have somehow learned to trick the olfactory system of mammals.
It turns out that out of 15 odorants, humans outperform dogs in detecting five, including β-Ionone (scent of cedarwood) and amyl acetate (scent of bananas). Also, humans are better than dogs at distinguishing certain scents (meaning, both feel them, but humans don’t confuse them while dogs do).
Or for instance, Carvone – caraway, dill, mandarin, orange. It exists in two isomeric forms (mirror images, same atoms), and its enantiomers smell differently: S(+)-carvone defines the scent of caraway and dill seeds, while its mirror isomer, R(-)-carvone, smells of spearmint (acute mint). This proves that humans have chiral scent receptors. It gets even more complicated with mixtures. A mixture of A and B can smell entirely different than A or B individually.
Then these receptors in the nose, they are generated from genes. There’s the OR7D4 gene, which creates a receptor that reacts to androstenone – what sweaty socks and body odor after a run smell like. For most, this scent is unpleasant. But there are some who have a slightly different version of this gene, and for them, androstenone smells like vanilla. Of course, this is hereditary. And that’s just one example. You can imagine how many similar situations there are with other genes. It turns out that we literally “see” the world differently in terms of scents. What one describes as the smell of sweaty socks might seem to another as the smell of vanilla, and if he has never smelled vanilla, he too will call it the smell of sweaty socks, until he encounters vanilla.
It also turns out that the best sniffers are elephants. Apart from the fact that their trunks are structurally better, there are more receptors and a healthy olfactory bulb. Lucy Bates describes an experiment where she took a bit of soil with remnants of their urine from behind a herd of elephants and transferred it hundreds of meters ahead on the herd’s path. Depending on whether it belonged to them, other elephants, or the same herd, the reaction was different. If it belonged to others, they simply walked on and did not notice. But if it belonged to one of them, the elephants were astounded, unable to understand how it could possibly be. It’s like if in our world, you entered a door on the left and came out of a door on the right. They couldn’t understand how the scent could be ahead when they were coming from another direction. The experiment also describes how an elephant can understand that out of a group of scientists who arrived in cars, there’s one newcomer, and he is in the third car on the back seat. It needs to approach him and smell.
Moreover, much is described about the olfaction of birds. Previously it was thought that they had none. Moreover, it turns out the ocean consistently emits a certain scent – dimethyl sulfide, a gas from plankton. And various oceanic birds use this scent pattern – which is plus or minus the same – for navigation.
It turns out that snakes cannot taste or smell with their tongues, but with their quick movements of the forked tongue, they take air samples and send them to the vomeronasal organ (or Jacobson’s organ) for analysis. This organ, by the way, is also present in dogs. With my Yuki, it’s very noticeable when he uses it, and when it’s the nose. Snakes do the same, only unlike dogs, they don’t have another olfactory organ. And we don’t have a vomeronasal organ.
Hi, I'm Rauf Aliev. 