and birds of
to-day no doubt surpass the cold-blooded dinosaurs of the Jurassic
age in mental qualities as they surpass them in physical structure.
From the codfish and turtle of ancient family to the modern lion,
dog, and monkey, it is a very long step upward. The mental life of
a warm-blooded animal is a very different affair from that of
reptiles and fishes. A squirrel or a bear does a good many things
in the course of his life. He meets various vicissitudes in
various ways; he has adventures. The actions he performs are so
complex and so numerous that they are severally performed with less
frequency than the few actions performed by the codfish. The
requisite nervous connections are accordingly not fully established
before birth. There is not time enough. The nervous connections
needed for the visceral movements and for the few simple
instinctive actions get organized, and then the creature is born
before he has learned how to do all the things his parents could
do. A good many of his nervous connections are not yet formed,
they are only formable. Accordingly he is not quite able to take
care of himself; he must for a time be watched and nursed. All
mammals and most birds have thus a period of babyhood that is not
very long, but is on the whole longest with the most intelligent
creatures. It is especially long with the higher monkeys, and
among the man-like apes it becomes so long as to be strikingly
suggestive. An infant orang-outang, captured by Mr. Wallace, was
still a helpless baby at the age of three months, unable to feed
itself, to walk without aid, or to grasp objects with precision.

But this period of helplessness has to be viewed under another
aspect. It is a period of plasticity. The creature's career is no
longer exclusively determined by heredity. There is a period after
birth when its character can be slightly modified by what happens
to it after birth, that is, by its experience as an individual. It
becomes educable. It is no longer necessary for each generation to
be exactly like that which has preceded. A door is opened through
which the capacity for progress can enter. Horses and dogs, bears
and elephants, parrots and monkeys, are all teachable to some
extent, and we have even heard of a learned pig. Of learned asses
there has been no lack in the world.

But this educability of the higher mammals and birds is after all
quite limited. By the beginnings of infancy the door f