their form, have been influenced by the third factor mentioned above,
but change the surroundings a little and the tendency appears. Free the
adult from the restraints of his ordinary life and turn him out for a
holiday and the childish tendencies of interest in novelty and the
mysterious, in physical prowess and adventure and play, all make their
appearance. In how many adults does the collecting instinct still
persist, and the instinct of personal rivalry? In how many has the crude
desire for material ownership or the impulse to punish an affront by
physical attack died out? Experimental evidence is even proving that the
general plasticity of the nervous system, which has always been
considered to be transitory, is of very, very much longer duration than
has been supposed.

In illustration of the third fact, namely, the effect of environment to
stimulate or repress, witness the "little mothers" of five and the wage
earners of twelve who have assumed all the responsibilities with all
that they entail of maturity. On the other side of the picture is the
indulged petted child of fortune who never grows up because he has had
everything done for him all his life, and therefore the tendencies which
normally might be expected to pass and give place to others remain and
those others never appear. That inborn tendencies do wax, reach a
maximum, and wane is probably true, but the onset is much more gradual
and the waning much less frequent than has been taken for granted. Our
ignorance concerning all these matters outweighs our knowledge; only
careful experimentation which allows for all the other factors involved
can give a reliable answer.

One reason why the facts of delayedness and transitoriness in instincts
have been so generally accepted without being thoroughly tested has been
the belief in the recapitulation or repeating by the individual of