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      Evidence: Epigenesis


           Epigenesis is another example of embodied context dependence. Epigenesis refers to the influence of the environment on the expression of the genetic code. Many genes require specific environmental circumstances in order to be expressed; many genes are never expressed. The genetic "program" refers to the potential for initiating and orchestrating specific physiological processes that may ultimately manifest themselves in a trait such as behavior.

FROM GENETIC CAUSE TO BEHAVIORAL CONSEQUENCE
examples of
INTERNAL
Environmental Components
Genetic Component is activated
examples of
EXTERNAL
Environmental Components
regulator and structural genes
promoters and enhancers activate and regulate genes when transcription factors attach to them
stability of the milieu interieur
(slight alterations in promoters can cause dramatic changes in gene expression)
availability of precursor molecules
Activity of other genes including physiological action and by-products of those actions


Orderly Enzyme Production

environmental influences
(various environmental factors can alter the transcription factors attachment to promoters)
enzymes
stability of the milieu interieur
availability of precursor molecules
carbohydrates, fats, proteins
Activity of other genes including physiological action and by-products of those actions


Regulated biochemical reactions

environmental influences
(various environmental factors can alter the speed or efficiency of biochemical reactions)
cell metabolism and development
stability of the milieu interieur
availability of precursor molecules
carbohydrates, fats, proteins
Activity of other genes including physiological action and by-products of those actions


organized development of nervous, skeletal, endocrine systems

environmental influences
(various environmental factors can alter the speed or efficiency of metabolism and construction or repair of tissues)
physiological mechanisms
stability of the milieu interieur
Activity of other genes including physiological action and by-products of those actions
latent or manifest memories of comparable phenomena


sensory perception, central nervous processing, commands to muscles

environmental influences
(various environmental factors can converge to affect what stimuli is perceived)
alternative behavioral patterns
stability of the milieu interieur
multiple parallel processing of information along competitive neural pathways


balance of inhibitory and facilitory information tips dynamic balance towards a specific behavioral pattern

environmental stimuli, real or perceived perceptions;
integration of information tips balance of inhibitory or facilitory impulses to cause a specific action(or sequence) to be manifest out of an array of alternative possibilities.

BEHAVIOR
once internalized (perceived) can feedback to activate or suppress further GENETIC ACTIVITY
in a continuing loop

A gene can produces several different polypeptide sequences but all not at the same time. For example, the lac operon can produce one enzyme in the presence of lactose but not in its absence. Some genes could produce one polypeptide when environmental conditions are one way, another when the environment changes. (FYI: an operon is a series of genes (DNA sequences) it includes an "inducer" (which makes a repressor protein) a "promoter," and an "operator." Suppose something goes wrong? some organisms seem to be able to carry on in some other way after a brief time)
adapted from Drickamer, Vessey, Meikle , Animal Behavior - 4th ed. Wm C Brown, 1997; Immelmann & Beer, A Dictionary of Ethology, 1989.