On 5/27/2012 a correspondent suggested that I may have confused proximate and ultimate causation, which he said was easily done. He indicated that epigenetics has no impact on the central doctrine of genes as the sole information carriers; that epigenetic effects are just one more way that allows genes to achieve their ultimate aim of replication. On 5/28/2012, the same correspondent suggested I look to a recent report that he thinks puts the excitement about epigenetics into context without shooting down that excitement. On 5/16/2012 provided my thoughts on this report by Dickins and Rahman in this blog post:
Here is a follow-up.
I may be confused about proximate and ultimate cause, especially if the role of transgenerational epigenetic inheritance is not central to the extended evolutionary synthesis. Isn’t transgenerational epigenetic inheritance the problem that led Dickins and Rahman to suggest a thought experiment; one where epigenetic mechanisms introduce shifts in learning bias for certain associations as would endocrine functioning? If so, my model (Kohl, 2012), which combines the epigenetic effects of nutrient chemicals and pheromones with biased endocrine functioning and adaptive evolution, may help move the modern synthesis forward.
I tried this before, but the RNA-mediated evolutionary continuum from microbes to man (Kohl, 2007) seems too much to grasp in the context of biased endocrine functioning. However, the honeybee has since emerged as a model organism to exemplify nutrient chemical and pheromone-dependent epigenetic alterations in endocrine functioning. These epigenetic effects that bias endocrine functioning are required for the adaptive evolution of reproduction.
Reproduction is required for transgenerational epigenetic inheritance and species diversity, which is perhaps better represented in the threespine stickleback vertebrate model organism. However, in all invertebrate and vertebrate model organisms, nutrient chemicals establish the ecological niche of individuals, and the presence of conspecifics establishes their social niche (as also occurs with microbial species).
The honeybee best exemplifies how ecological and social niches contribute to the hypothalamic gonadotropin releasing hormone (GnRH) neurogenic niche that is responsible for the adaptive evolution of the human brain. Simply put, what the queen eats determines her pheromone production and everything else about the social interactions in the colony, including the required epigenetic effects of pheromones on the neuroanatomy of the worker bee’s brains during the development of their diverse behaviors that change with exposure to different chemical input associated with a variety of other sensory input of lesser importance / salience.
Of course, that sounds too simple in the context of the extended evolutionary synthesis and human brain evolution. But the molecular biology is conserved across species, which is helpful for proof of concept. In placental mammals, for example, in utero nutrient chemical transfer is responsible for organization of the brain’s postnatal activation by nutrient chemicals and pheromones. The proper GnRH-driven behavioral response of the infant to activation by these chemicals ensures its survival, just as the proper response of the honeybee worker bee’s brain to nutrient chemicals and pheromones ensures its survival and helps to ensure the colony’s survival via changes in the neuroanatomy of its brain. (Parenthetically, spectral input may or may not be correlated with direct epigenetic effects on the brain, but it is not causal to brain development.)
Model organisms have their molecular biology in common with all other organisms. No organism survives in the absence of sufficient nutrient chemicals. Ecological niches contract. And no species survives in the absence of reproduction controlled by pheromones. I think that’s why we are now seeing more reports on transgenerational epigenetic inheritance, with causal links to speciation via ecological and social niches in all species. We should soon see the addition of neurogenic niches in many others.
What I don’t see is anyone who is integrating the ecological, social, and neurogenic niches and considering the epigenetic effects of nutrient chemicals and pheromones in the context of endocrine disruption and transgenerational epigenetic inheritance. Nutrient chemicals and pheromones promote homeostasis and also allow adaptive evolution, including adaptive evolution of the human brain. Endocrine disruption causes atypical development of the brain and the body.
Isn’t that the apparent design we might all someday see in biology? Isn’t seeing the apparent design required to move forward from the Modern Synthesis to the Extended Evolutionary Synthesis?