greater becomes the revolution when a certain
process goes on Until it sets going a number of other processes,
unlocking series after series of causal agencies until a vast and
complicated result is reached, such as could by no possibility have been
foreseen. The creation of Man was one of these vast and complicated
results due to the unlocking of various series of causal agencies; and
it was the beginning of a deeper and mightier difference in kind than
any that slowly evolving Nature had yet witnessed.

I have indicated, as the moment at which the creation of mankind began,
the moment when psychical variations became of so much more use to our
ancestors than physical variations that they were seized and enhanced by
natural selection, to the comparative neglect of the latter. Increase of
intellectual capacity, in connection with the developing brain of a
single race of creatures, now became the chief work of natural selection
in originating Man; and this, I say, was the opening of a new chapter,
the last and most wonderful chapter, in the history of creation. But the
increasing intelligence and enlarged experience of half-human man now
set in motion a new series of changes which greatly complicated the
matter. In order to understand these changes, we must consider for a
moment one very important characteristic of developing intelligence.

The simplest actions in which the nervous system is concerned are what
we call reflex actions. All the visceral actions which keep us alive
from moment to moment, the movements of the heart and lungs, the
contractions of arteries, the secretions of glands, the digestive
operations of the stomach and liver, belong to the class of reflex
actions. Throughout the animal world these acts are repeated, with
little or no variation, from birth until death, and the tendency to
perform them is completely organized in the nervous system before birth.
Every animal breathes and digests as well at the beginning of his life
as he ever does. Contact with air and food is all that is needed, and
there is nothing to be learned. These actions, though they are performed
by the nervous system, we do not class as psychical, because they are
nearly or quite unattended by consciousness. The psychical life of the
lowest animals consists of a few simple acts directed toward the
securing of food and the avoidance of danger, and these acts we are in
the habit of classing as instinctive. They are so simple, so few