y specialized to
reproduce themselves.

What transfigures the individual as the years go by is no simple wear
and tear of the tissues, nor the replacement of old cells by new. It
is the rearrangement of relationships among the ductless glands, the
shifting of influences from the predominant to the subordinate, and
vice versa, in the constellation of the internal secretions, that
determines the unfolding of the personality. The transformations raise
doubt sometimes as to the reality of personal identity. What actually
happens in the changes from childhood to adolescence, from adolescence
to maturity, and so on, is the sloughing of one internal glandular
dominance for another.

Growth, as a general name for the mutations, the ensemble of somatic
and psychic differentiation, from year to year, passes through five
epochs that are standard for the normal. The normal is the being who
harmonizes with his environment, and yet reacts with it because of
recurring needs within him. His endocrine equation settles what is
unique and different in him. But the gland which flourishes during the
epoch as its time of triumph, when it has its day, determines what
makes him like his fellows.

From this point of view it becomes permissible to speak of the five
Endocrine Epochs. Similarities and resemblances of mind and body
between people at a given period of life, childhood, youth, maturity
must be put down to their common government by the salient endocrine
of the epoch. So one may list:

Infancy as the epoch of the thymus
Childhood as the epoch of the pineal
Adolescence as the epoch of the gonads
Maturity as the epoch of whatever gland is left in control as the
result of the life struggle.
Senility as the epoch of general endocrine deficiency.

Infancy as the epoch of the thymus explains why, in any given
geographic locality, the babies look alike and act alike. Specialists
in the observation and treatment of infants have noted that not until
after the second year is any tendency to differentiation discernible
to any extent among them. It is only after the second year, or
somewhere around that time, that the child begins to individuate, and
distinct individual traits and a personality manifest their outlines.
The thymus is the great inhibitor of all the glands of internal
secretion. By its checking activity upon the other members of the
endocrine system, the thyroid and pituitary in particular, it gives
the baby time