Adaptive ‘noise’

By: James V. Kohl | Published on: August 1, 2013

Adaptive noise

Article conclusion:Understanding what generates and maintains phenotypic variation is a key aim of evolutionary biology, and it is now clear that noise contributes significantly to phenotypic variation; if noise has an important role in evolution, we cannot afford to ignore it.

My comment: These authors are labeling something ‘noise’ and inferring we cannot afford to ignore it. I think I know what they think is ‘noise,’ and why it cannot be ignored in the context of the important role of genetic predispositions and olfaction in evolution. For example, we have a clear view of what cannot be ignored from the abstract of “Genome-wide Association Mapping of Natural Variation in Odor-guided Behavior in Drosophila”:  “A defining goal in the field of behavioral genetics is to identify the key genes or genetic networks that shape behavior,” which ultimately explains how “…subtle changes influencing nervous system function can result in marked differences in behavior.

It could not be clearer to me that what some people call ‘noise’ is the epigenetic effect of the sensory environment, which generates and maintains phenotypic variation. What’s been learned about epigenetics all but eliminates the gene-centric opinions of the past (see for example: Rethinking the (im)possible in evolution). Today, we know that “[A]t the highest level of chromatin organization, the epigenetic ‘‘landscape’’ becomes a physical landscape where particular genes and regulatory sequences are hidden or exposed in accordance with the cell type and function.‘ (p. 735). Simply put, whether or not anyone accepts this physiological fact,  the epigenetic ‘landscape’ becomes the physical ‘landscape’ of DNA via alternative splicings, which are responsible for phenotypic variation (see for review From Fertilization to Adult Sexual Behavior). But wait, what can simply be said about the physiology of everything that occurs during the time from fertilization to adult sexual behavior?

Does olfactory/pheromonal input epigenetically effect everything involved in the development of human behavior? If animal models offer acceptable proof, the answer to that question is a resounding YES!

In mammals, what the authors of “Adaptive Noise” call ‘noise’ is ‘silenced’ when the epigenetic effects of olfactory/pheromonal input on gene activation in neurosecretory cells in the brain are associated via complex systems biology with less direct effects of other sensory input on networks of neurosecretory neurons that alter secretion of gonadotropin releasing hormone (GnRH).  This hormone, GnRH is the biological core of nutrient-dependent pheromone-controlled reproduction. Glucose uptake and pheromones control GnRH, which controls reproduction. GnRH controls the nutrient-dependent adaptive evolution of mammals via its control of reproduction.

The mammalian GnRH neuronal system has its embryonic origin in the nose, and ‘Feedback loops link odor and pheromone signaling with reproduction’ via the nose.  Thus, it becomes clear “… that GnRH peptide plays an important role in the control of sexual behaviors…” That suggests “…pheromone effects on these behaviors might also involve GnRH neurons.” (p 683). Is this more than merely a suggestion of cause and effect? YES!

The reason I’m paraphrasing with quotes and providing links to cited works is to make something clear. More than two decades ago it was known that: “Noradrenergic, dopaminergic, serotoninergic, and opiotergic pathways; inhibitory neurotransmitters (e.g., gamma aminobutyric acid) and excitatory amino acids (e.g., glutamic and aspartic acids); and other brain peptides including pineal secretions (melatonin) and corticotrophin releasing hormone affect the LHRH [GnRH] pulse generator (Grumbach & Styne, 1992 cited in Kohl, 2006).” When I mentioned that fact recently, a discussant referred to it as “neurochemical gibberish.” However, the demonstration by Herde et al (2013) of  the dynamic control of GnRH secretion into the pituitary portal system to regulate fertility (i.e., nutrient-dependent pheromone-controlled reproduction) extends the dynamic control of GnRH secretion from Nobel Laureate Linda Buck’s  ‘Feedback loops [that] link odor and pheromone signaling with reproduction’ to Nobel Laureate Sir Paul Nurse’s Life, logic and information. The pulsatile secretion of GnRH extends virtually everything currently known about behavioral genetics to my model of the conserved molecular mechanisms in species from microbes to man in which “Olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans.

Here’s what’s currently known.

1) In insects, food odors and pheromones epigenetically effect genetically predisposed hormone-organized and hormone-activated behaviors.

2) In mammals, food odors and pheromones epigenetically effect genetically predisposed hormone-organized and hormone activated behaviors

(see for review Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors).

There are conserved molecular mechanisms across species of insects and mammals that clearly link olfactory/pheromonal input to the development of species specific behaviors that are required for species survival: nutrient aquisition and reproduction. Thus, we can now reach the same conclusion reached by Lewis Thomas more than 30 years ago: “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.“– as cited in The Scent of Eros: Mysteries of Odor in Human Sexuality.

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