Epigenetics: Core misconcept by Mark Ptashne. PNAS 2013 110 (18) 7101-7103
Article excerpt: “The important point is to attend to how things actually work.”
My comment: See also: “…behavioral epigenetics has yet to connect all its levels of analysis. It needs, and doesn’t yet have, at least one slam-dunk demonstration of all the links in a chain from behavior to neural activity to gene expression and back out again.”
The “slam-dunk demonstration” of how things actually work is found in the context of nutrient-dependent pheromone-controlled adaptive evolution. Nutrient acquisition alters the microRNA / messenger RNA balance as receptor-mediated interactions enable nutrients to enter cells. That’s how experiences associated with nutrient acquisition link the “epigenetic landscape” to the “physical landscape” of DNA via alterations in the microRNA / messenger RNA balance. Experience-dependent epigenetic effects of sensory input cause changes in the microRNA / messenger RNA balance and intracellular signaling that result in intermolecular changes and chromatin remodeling. Epigenetic effects on chromatin remodeling result in de novo expression of nutrient-dependent genes, including the expression of genes in nerve cells that link nutrient acquisition to neural activity and to neural Darwinism (see below).
In species that sexually reproduce, de novo gene expression in any tissue might otherwise lead to runaway selection if only mutations significantly altered gene expression. However, the metabolism of acquired nutrients to species-specific pheromones is genetically predisposed. That’s how pheromones control what might otherwise result in uncontrolled mutation-associated reproduction in species from microbes to man. That’s also why mutation-driven natural selection for species-specific phenotypic traits is a ridiculous misrepresentation of biological facts. Simply put, there is no model of natural selection for species-specific mutations.
Instead, it is clear that pheromones ensure genetically predisposed nutrient acquisition behavior drives adaptive evolution, which is controlled by the epigenetic effects of species-specific pheromones on feedback loops. These feedback loops link behaviors associated with reproduction to behaviors required for nutrient acquisition in species from microbes to man.
Behaviors associated with individual acquisition of nutrients and metabolism of a novel nutrient source are associated with beneficial changes in the thermodynamics of intracellular signaling which result in beneficial changes in organism-level thermoregulation. Species survival is modulated by species-specific thermoregulation directly linked to the epigenetic effects of pheromones on behaviors like mate selection and behaviors associated with additional nutrient acquisition.
In my model, for example, nutrient availability controls ecological niche construction. The metabolism of nutrients to pheromones controls social niche construction. Social niche construction controls reproduction. Neurogenic niche construction occurs in the context of nutrient-dependent pheromone-controlled reproduction and leads to socio-cognitive niche construction. In mammals, this epigenetically links socio-cognitive niche construction to nutrients like glucose via the effects of glucose on gonadotropin releasing hormone (GnRH). In mammals, this also links socio-cognitive niche construction to pheromone via the epigenetic effects of species-specific pheromones on GnRH.
In the context of cognition, a recent report stated: “Competitive mechanisms appear to be in place that link neuron activity and growth to as yet fully defined reward on the molecular level. Such neural Darwinism might simply be the struggle for access to nutrients from the vasculature, like glucose and oxygen, and to dispose of metabolites, like transmitter byproducts. These processes might be enhanced by making the right synaptic partners residing on coveted real estate, and spiking most often at the right time to greatest effect.”
This “neural Darwinism” occurs only in the context of detailed nutrient-dependent pheromone-controlled rewards, and is exemplified at the molecular level in my model. Of course, neural Darwinism can be represented as the struggle of nerve cells for access to nutrients, but this struggle obviously involves the adaptive evolution of nerve cells long before it incorporates epigenetic effects on nutrient-dependent neurogenesis and the neurogenic niche construction of neural Darwinism. This can be seen across the evolutionary continuum in which the alpha mating pheromone of brewer’s yeast elicits a hormone response from the cultured pituitary cells of rats. Species-specific mammalian pheromones and glucose also elicit the same hormone response, which is modulated by gonadotropin releasing hormone (GnRH).