f man.

One of the races of quadrumanous animals which had reached the highest
state of perfection, lost, by constraint of circumstances (concerning
the exact nature of which tradition is unfortunately silent), the habit
of climbing trees, and of hanging on by grasping the boughs with their
feet as with hands. The individuals of this race being obliged, for a
long series of generations, to use their feet exclusively for walking,
and ceasing to employ their hands as feet, were transformed into
bimanous animals, and what before were thumbs became mere toes, no
separation being required when their feet were used solely for walking.
Having acquired a habit of holding themselves upright, their legs and
feet assumed, insensibly, a conformation fitted to support them in an
erect attitude, till at last these animals could no longer go on
all-fours without much inconvenience.

The Angola orang (_Simia troglodytes_, Linn.) is the most perfect of
animals; much more so than the Indian orang (_Simia Satyrus_), which has
been called the orang-outang, although _both_ are _very inferior_ to man
in corporeal powers and intelligence. These animals frequently hold
themselves upright; but their organization has _not yet_ been
sufficiently modified to sustain them habitually in this attitude, so
that the standing posture is very uneasy to them. When the Indian orang
is compelled to take flight from pressing danger, he immediately falls
down upon all-fours, showing clearly that this was the original position
of the animal. Even in man, whose organization, in the course of a long
series of generations, has advanced so much farther, the upright posture
is fatiguing, and can be supported only for a limited time, and by aid
of the contraction of many muscles. If the vertebral column formed the
axis of the human body, and supported the head and all the other parts
in equilibrium, then might the upright position be a state of repose:
but, as the human head does not articulate in the centre of gravity, as
the chest, belly, and other parts press almost entirely forward with
their whole weight, and as the vertebral column reposes upon an oblique
base, a watchful activity is required to prevent the body from falling.
Children who have large heads and prominent bellies can hardly walk at
the end even of two years; and their frequent tumbles indicate the
natural tendency in man to resume the quadrupedal state.

Now, when so much progress had been made