gence. For what
need was there for brain and intelligence when food lay about so
abundantly at hand for them to gorge themselves. As there was no
competition for food, there were no enemies.

Then as the earth evolved and grew cooler, vegetation failed, the
ancestors of the present carnivora appeared, the fathers of the
wolf and tiger, light, lithe and pugnacious, with senses acute and
ferocious weapons of attack, who set out to destroy everybody. They
destroyed pretty nearly all of the huge leaf-eating species, and only
the more plastic and smaller ones, who were more keen-sensed and
swift-footed (of whom the deer and antelope, horse and ox are the
descendants), escaped. The smallest either took to the air to become
the bat, or, like the forerunners of the squirrel and ape, took to the
trees.

It was the coming of the carnivores, therefore, that accelerated the
development of brain matter, and started the process which created
man. But in the millions and millions of years of conflicts, instincts
grew into being that sank deep into bone and marrow. The most
fundamental reflexes, those immediate responses to irritation or
danger, were laid down, and among them the drive and check system.
When the animal had decided to fight its enemy or was forced to fight,
or determined to prey, then was the time for the drive system to do
its utmost to speed up everything that would help in the fight, while
the check system came into play to hinder whatever would interfere or
burden in the fray. First the drive mechanism must have been hit upon,
and then the value of the check devices must have been found in fear
and flight, and especially in hiding and simulation of death, when
even breathing had to be inhibited. Until finally there developed, for
everyday use, a complete check and drive nerve machinery for every
organ, to be used according to the exigencies of the moment, with the
thyroid as the primary stimulant and controller of the drive system
and the adrenal as the primary dictator over the check system.

THE HARMONY OF THE HORMONES

All the glands, in fact, work in unison, with a distribution of the
balance of power that diplomatists might envy. In the co-ordinating
synchronism, the vegetative nervous system plays the part of an agent
that acts as well as is acted upon. The chemical interaction of the
internal secretions is not the only way in which they influence each
other. For, as the case of the thyroid and the adrena