We can sum up the few attainments of mammals in a line.  The lower forms attained the placental mode of embryonic development; the higher attained upright gait, hands and feet, and a great increase of brain.  Anatomically considered these were but trifles, but the addition of these trifles revolutionized life on the globe.  The principal anatomical differences between man and the anthropoid ape are the following:  Man is a strictly erect animal.  The foot of the ape is less fitted for walking on the ground, where he usually “goes on all fours.”  The skull is almost balanced on the condyles by which it articulates with the neck, and has but slight tendency to tip forward.  The facial portion, nose and jaws, is less developed and retracted beneath the larger cranium or brain-case.  This has greatly changed the appearance of the head.  Protruding jaws and chin, even when combined with large cranium and brain, always give man the appearance of brutality and low intelligence.

The pelvis is broad and comparatively shallow.  The legs, especially the thighs, are long.  The foot is long and strong, and rests its lower surface, not merely the outer margin as in apes, on the ground.  The elastic arch of the instep must be excepted in the above description, and adds lightness and swiftness to his otherwise slow gait.  The great toe is short and generally not opposable.  The muscles of the leg are heavy and the knee-joint has a very broad articulating surface.  But the great result of man’s erect posture is that the hand is set free from the work of locomotion, and has become a delicate tactile and tool-using organ.  The importance of this change we cannot over-estimate.  The hand was the servant of the brain for trying all experiments.  Had not our arboreal ancestors developed the hand for us we could never have invented tools nor used them if invented.  And its reflex influence in developing the brain has been enormous.  The arm is shorter and the hand smaller.  The brain is absolutely and relatively large, and its surface greatly convoluted.  This gives place for a large amount of “gray matter,” whose functions are perception, thought, and will.  For this gray matter forms a layer on the outside of the brain.

Thus, even anatomically, man differs from the anthropoid apes.  His whole structure is moulded to and by the higher mental powers, so that he is the “Anthropos” of the old Greek philosophers, the being who “turns his face upward.”  Yet in all these anatomical respects some of the apes differ less from him than from the lower apes or “half apes.”  And every one of these can easily be explained as the result of progressive development and modification.  Whoever will deny the possibility or probability of man’s development from some lower form must argue on psychological, not on anatomical, grounds; and it grows clearer every day that even the former but poorly justify such a denial.