t-armed animal, a
condition the reverse of that seen in the anthropoid apes. While man's
hands reach barely to the middle of the thigh, those of the chimpanzee
reach below the knee, of the gorilla to the middle of the leg, of the
orang to the ankle, and of the gibbon to the ground. All these apes have
short legs and long arms. Man, on the contrary, has long legs and short
arms.

The natural presumption from this interesting fact is that man's
ancestor, which we may provisionally call the man-ape, differed
essentially in its mode of progression from the other apes. The smaller
forms of these usually move on all fours in the trees, though the arms
are always ready for a swing or a climb. The anthropoid apes also show a
tendency to a similar mode of progression, though with a difference in
their mode of walking, which, as we shall see later on, is never that of
the quadruped. As for the man-ape, it may have originally walked in the
same manner as the related species, if we surmise that the variation in
the length of the limbs was a subsequent development. Certainly after
its limbs attained the proportions of those of man, its facility of
swinging from tree to tree must have been diminished, while it would
have found it inconvenient to move in the crouching attitude of the
orang and its fellows. Its easiest attitude must then have been the
erect one, and its motion a true biped walk, not the swinging and
jumping movement of the other anthropoids. In short, the development of
man's ancestor into a short-armed animal, however and whenever it took
place, could not but have interfered seriously with its ease of motion
in the trees. Though this change may have begun in the trees, it
probably had its full development only after the animal made the ground
its habitual place of residence.

It is of interest to find that all the existing large apes are
arboreal, the gorilla being the least so, probably on account of its
weight. Though they all descend at times to the ground, their awkward
motion on the surface shows them to be out of their element, while they
move with ease and rapidity in the trees. The organization of man
renders it questionable if his primeval ancestor was arboreal to any
similar extent. The indications would seem to be that it made the ground
its habitual place of residence at an early period in its history, and
that the result of this new habit and of its erect attitude was a change
in the relative length of