The motor program generators are established in the developing nervous
system by the DNA. When triggered, they produce motor activity. We
ask, "How are they triggered?"
The sensory neurons transduce the energy of the universe as it arrives
at the body surface. They also transduce energy from the internal
condition of the body. The resultant signal energy filters through the
interneurons and, when it summates at a given motor program generator,
it triggers the generator.
The paths that the signal energy traverses are originally set up by
the DNA. I emphasize that the nervous system is precisely connected
before and after birth to be prepared to handle an unfriendly universe
that previous generations encountered. When the organism meets up with
the present milieu, there is a tremendous pruning and die-off of
synapses and neurons.
There is a reorganization of synapses (called learning by some) as the
organism masters the location of food and water sources and the
position of secure resting places. Later there is the problem of
mates. The paths through which the signal energy passes are altered so
that the appropriate motor program generators are triggered so as to
First place is given to avoidance of the predator.