The perceptual logic of smell (a review of experimental evidence)

The perceptual logic of smell   Review Article 

Current Opinion in Neurobiology, Volume 25, April 2014, Pages 107-115
Lavi Secundo, Kobi Snitz, Noam Sobel

Abstract excerpt: “…we speculate that olfaction likely does not functionally rely on 1000 different receptor subtypes, and their persistence in evolution may imply that they have additional roles in non-olfactory functions such as in guidance of embryogenesis and development.”

Article excerpt: “As far as we know, flies do not have an inordinately high number of specific anosmias, and will typically perform any olfactory discrimination task in the lab, and again, all this with only ~60 receptor subtypes. So why do mammals need 1000?”

Article conclusion: The simplicity of olfactory perception implies that the complexity of the olfactory genome may hold secrets for more than understanding olfaction alone.

Historical perspective: Lewis Thomas (1980) “I should think we might fairly guage the future of biological science, centuries ahead by estimating the time it will take to reach a complete comprehensive understanding of odor. It may not seem a profound enough problem to dominate all the life sciences, but it contains, piece by piece, all the mysteries.

My comment: Noam Sobel, who co-authored this review, initially appeared to be the most argumentative researcher I had ever encountered. He also seemed physically threatening, which made me happy that he was not arguing with me. Like others who have argued with “experts,” Noam has since elaborated on the common theme that pairs details of my ecological adaptations model with this review via embryogenesis and behavioral development. Ecological adaptations, embryogenesis, and behavioral development in mammals are closely linked to olfaction and odor receptors. They  “…provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans

Sobel’s group has consistently helped to make scientific progress via integrative approaches supported by experimental evidence. In this review, the authors dispense with misrepresentations made about the importance of the comparative number of olfactory receptor genes in different species. Those misrepresentations have been used to support species differences. This reveiw helps to draw focus on the conserved mechanisms of molecular epigenetics that link species from microbes to man via ecological, social, neurogenic, and socio-cognitive niche construction that is nutrient-dependent and pheromone-controlled.

A brief review of the historical perspective on The perceptual logic of smell (sans mutations theory) may help others to understand my perspective and why I think it is shared by Noam Sobel. Simply put, I agree with everything Lewis Thomas ever wrote or inferred about the sense of smell and the role of human pheromones in the development of human behavior.

The act of smelling something, anything, is remarkably like the act of thinking.” – p 732

No other animal appears to think about what it is smelling or not smelling.

A Fear of Pheromones “WHAT are we going to do if it turns out that we have pheromones? What on earth would we be doing with such things?”

Thinking about human pheromones still frightens some people.

Secundo, Snitz and Sobel’s “…non-olfactory functions such as in guidance of embryogenesis and development” have already been linked to Mosaic Copy Number Variation in Human Neurons. The link is from nutrient-dependent pheromone-controlled amino acid substitutions and chromosomal rearrangements. “One straightforward hypothesis is that neurons with different genomes will have distinct molecular phenotypes because of altered transcriptional or epigenetic landscapes.”

I am not aware of any other straightforward hypothesis that is based on what is currently known about the basic principles of biology and levels of biological organization required to link sensory input to hormone-organized and hormone-activated behaviors in insects and mammals. For contrast, olfactory/pheromonal input links the perceptual logic of smell from the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man.


Author: James Kohl

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