_. There is still another
group of inherited tendencies connected with sex and reproduction, which
are not discussed in this book.

We shall give a brief discussion of the instincts falling under these
various classes. It must be remembered, however, that the psychology of
the instincts is indefinite and obscure. It is difficult to bring the
instincts into the laboratory for accurate study. For our knowledge of
the instincts we are dependent, for the most part, on general
observation. We have had a few careful studies of the very earliest
years of childhood. However, although from the theoretical point of view
our knowledge of the instincts is incomplete, it is sufficient to be of
considerable practical value.

=The Individualistic Instincts.= Man's civilized life has covered but a
short period of time, only a few hundred or a few thousand years. His
pre-civilized life doubtless covered a period of millions of years. The
inborn tendencies in us are such as were developed in the long period of
savage life. During all of man's life in the time before civilization,
he was always in danger. He had many enemies, and most of these enemies
had the advantage of him in strength and natural means of defense.
Unaided by weapons, he could hardly hold his own against any of the
beasts of prey. So there were developed in man by the process of natural
selection many inherited responses which we group under the head of
_fear_ responses.

Just what the various situations are that bring forth these responses
has never been carefully worked out. But any situation that suddenly
puts an individual in danger of losing his life brings about
characteristic reactions. The most characteristic of the responses are
shown in connection with circulation and respiration. Both of these
processes are much interfered with. Sometimes the action is accelerated,
at other times it is retarded, and in some cases the respiratory and
circulatory organs are almost paralyzed. Also the small muscles of the
skin are made to contract, producing the sensation of the hair standing
on end. Just what the original use of all these responses was it is
difficult now to work out, but doubtless each served some useful
purpose.

Whether any particular situations now call forth inherited fear
responses in us is not definitely established. But among lower animals
there are certain definite and particular situations which do call forth
fear responses. On the whole, the evi