Biology Reference
In-Depth Information
Where Is the Epigenetic Information for TDPs Generated?
This is a logical question. A new trait requires information for a new spatiotemporal
pattern of arrangement of millions of cells of several types (morphological and/or
life history change) or the reorganization or addition of new neurons to form a spe-
cial neural circuit (behavioral and/or life history change). As explained in Chapter 2,
the genetic information for protein biosynthesis does not play a factor. Theoretical
speculations aside, it is firmly and unequivocally determined that no changes in
genes occur or are related with TDPs.
Reported cases of TDP arise in response to stressful stimuli or conditions and
contribute to an organism's fitness. They are almost always adaptive, rather than ran-
dom changes.
The pathway from receiving the environmental stimulus, to its processing in the
animal's brain, to the maternal/paternal factors in the egg cell that determine the phe-
notypic change in the offspring, is complex and, in many essential details, unknown.
All that can safely be done here is to review the empirical evidence and then look for
possible leads that may allow for the outlining of the mechanics of a stimulus' trans-
lation, via individual development, into a new phenotypic character in the offspring.
The importance of researching TDPs, from a theoretical point of view, can hardly
be overstated because it offers a mechanism of induction in the offspring for one to
several generations of a trait that the parents, themselves, lack. The transmission of
the new trait involves no change in genes, defying the basic neo-Darwinian tenet that
genes are the only determinants of inherited traits.
The stimulus has no direct relevant effect on any cell or gene. It is in the brain
where it is decoded and the response is determined. So, for example, decapitated
females of the cowpea aphid, Aphis craccivora Koch ( Johnson and Birks, 1960 ) and
of Megoura viciae Buckton of the Aphidinae subfamily ( Lees, 1967 ) that have been
cued (by crowding-related tactile stimulation) to produce winged offspring, produce
only wingless insects, clearly indicating that signals for wing development originate
in the brain. This was the investigators' assessment:
Wing dimorphism is apparently controlled by a diffusible “alata-determiner” liber-
ated from the head of the parent.
Lees (1967)
A common misconception is that environmental stimuli are associated with some
kind of information or instruction that tells the organism, or even genes, what to do.
This is not the case. The stimulus poses a problem that the organism must cope with.
As already pointed out, no environmental stimulus, per se , can randomly, let alone
adaptively, induce the expression of any gene or trigger any signal cascade. The epi-
genetic information to trigger a signal cascade or induce a particular gene is gener-
ated after processing the stimulus in the brain. That information is the output of the
neural processing released as a chemical/electrical signal. The probability of induc-
ing the TDP here increases from 0 (the probability that the environmental stimulus
can induce it) to 1 and satisfies Shannon's definition of information.
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