Experimental evidence and examples vs opinions
February 22, 2014 | James Kohl
The Age of Olfactory Bulb Neurons in Humans (2012, senior author Frisén)
Abstract excerpt: Results show that olfactory bulb neurons in humans are as old as the individual and argue that adult olfactory bulb neurogenesis is minimal in humans.
Journal article conclusion: “Functional studies in rodents have implicated adult neurogenesis in olfactory memory formation, odorant discrimination, and social interactions (Lazarini and Lledo, 2011). The lack of comparable adult olfactory bulb neurogenesis in humans poses the question whether these functions are mediated by conceptually different mechanisms in humans, or whether the more limited dependence on olfaction in humans compared to rodents in part may be due to the lack of one type of plasticity, adult neurogenesis.”
Reported as: No new neurons in the human olfactory bulb
Excerpt: “This is a strong indication that there is no significant generation of new neurons in this part of the brain, something that sets humans apart from all other mammals.”
My comment: Experimental evidence clearly shows that conserved molecular mechanisms link the epigenetic landscape to the physical landscape of DNA in the organized genome of species from microbes to man via olfactory memory formation, odorant discrimination, and social interactions. Food odors and social odors link ecological variation from the impact of olfactory/pheromonal input in rats to the differentiation of our cell types and to our morphological and behavioral phenotypes. The importance of acknowledging the conserved molecular mechanisms is apparent in the following article about:
By Kate Yandell | February 20, 2014
Excerpt: Eventually, Frisén and his colleagues’ findings could impact regenerative medicine research and the treatment of neurodegenerative diseases.
My comment: In less that two years, Frisén and his colleagues’ findings have gone from denying the similarities across species of mammals, to exemplifying them. What appears to have not changed is Frisén’s opinion about the importance of the sense of smell in rats compared to its importance in humans.
2012 “Humans are less dependent on their sense of smell for their survival than many other animals, which may be related to the loss of new cell generation in the olfactory bulb…” says Professor Frisén.
2014 “It is clear that we are much less dependent on olfaction—and have a less developed sense of smell—than most other mammals,” Frisén explained in an e-mail to The Scientist.
My [edited] comment to the Scientist:
The perceptual logic of smell “…growing recent evidence for expression of olfactory receptors in non-chemosensory tissue” implies that “..the complexity of the olfactory genome may hold secrets for more than understanding olfaction alone.”
This model details how chemical ecology drives adaptive evolution via: (1) ecological niche construction, (2) social niche construction, (3) neurogenic niche construction, and (4) socio-cognitive niche construction. This model exemplifies the epigenetic effects of olfactory/pheromonal conditioning, which alters genetically predisposed, nutrient-dependent, hormone-driven mammalian behavior and choices for pheromones that control reproduction via their effects on luteinizing hormone (LH) and systems biology.
Pheromones and the luteinizing hormone for inducing proliferation of neural stem cells and neurogenesis links my “atoms to ecosystems” approach from food odors and pheromones to neurogenic niche construction, neurodegenerative diseases and to morphological and behavioral phenotypes in species from roundworms to humans.
For example, see: System-wide Rewiring Underlies Behavioral Differences in Predatory and Bacterial-Feeding Nematodes “We uncover a massive rewiring in a complex system of identified neurons, all of which are homologous based on neurite anatomy and cell body position.”
No experimental evidence suggests that “…we are much less dependent on olfaction—and have a less developed sense of smell—than most other mammals….” That is an ecologically invalidated opinion, which Professor Frisén’s work helps to expose in the context of neurogenic niche construction.
It is also an opinion that is biologically implausible. Like other opinions about cause and effect, it must be placed into the context of the ecological adaptations that enable neurogenic niche construction. Clearly, we cannot be any less dependent on olfaction for nutrient acquisition or the nutrient-dependent pheromone-controlled physiology of our reproduction than any other organism with conserved molecular mechanisms. And those mechanisms link the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man. The organized genomes in roundworms are organized by the molecular mechanisms that enable neurogenic niche construction in humans.
In that context, opinions about the relative salience of different types of sensory input, which epigenetically effect the molecular mechanisms that affect behavior, and opinions about the primacy of our sense of smell defy The perceptual logic of smell. Ernst et al., tells us it is time for our opinions to become acquainted with biological facts about ecological, social, neurogenic, and socio-cognitive niche construction.
Addendum: Even when it is Frisén who reports results that imply he previously misrepresented biological facts, his opinion about the importance of the human sense of smell compared to its importance in other mammals has not changed. The question arises: why waste time on experiments that provide evidence if the experimental evidence does nothing to change your opinions about the conserved molecular mechanisms of biologically-based cause and effect? However, perhaps the science journalist do not know how to ask scientists the right questions, which would enable accurate reporting of their results.