Smell is a Sense More Suited to a Fluid Medium

Image source: The Human Brain, Rita Carter, 2009

Smelling started in fish. But that’s not exactly true, because responding to chemical signals is something that has been happening since life’s very beginning. Smelling with a brain...that starts with fish.

Neil Shubin, and ichtyopaleontologist (fish fossil finder), believes that the best roadmaps to our own bodies can be found in other creatures, as they carry the story of our development in their bones as well as their DNA. According to Subin's 2008 book Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body, there are two kinds of smelling genes in animals. One is for chemo-signaling in the air and one is for water. But certain surf and turf animals, the jawless fish (lampreys and hagfish), have both types, suggesting they arose before smelling genes split in two.

These jawless fish also have fewer odor genes. Over evolutionary time they increase – humans have hundreds. Many of our genes are non-functioning (and many are still in the process of evolving even today). Nonetheless, these junk genes remain in our DNA as a silent record of our evolution.

Geneticist Yoav Gilad found that primates who develop color vision tend to have more junk odor genes. Vision as an information tool de-emphasizes smell, thus turning more and more odor genes into junk. The (simple) advent of bipedalism takes us further from the data-rich olfactory carpet, while at the same time reinforcing the benefits of being so high up – we can see so much more this way!

It is no coincidence also, that the higher processing areas of our brain developed in tandem with the visual areas. Vision lends itself to cognition, whereas smell is limited to our emotions.

In the silent record of our evolution, manifest in our neuro-anatomy, is this separation between thoughtful human and primitive animal, the reflective and the automatic. To see is to understand. But to smell is to remember what it was like for the first organism to brainitself out of timespace, to be a jawless fish, a nematode worm, a plant whose roots wiggle through the earth, or the eukaryote "mindlessly" following the chemical gradient. There is no soil, no air, only fluid chemical signatures to activate and inhibit, and to be stored in memory forever.

Then again, they say fish only remember 7 seconds.