"Animal forms then are the result of conditions of life and of the habits engendered thereby. With new forms new faculties are developed, and thus nature has little by little evolved the existing differentiations of animal and vegetable life."[316] Lamarck makes no exception in man's favour to the rule of descent with modification. He supposes that a race of quadrumanous apes gradually acquired the upright position in walking, with a corresponding modification of the feet and facial angle. Such a race having become master of all the other animals, spread itself over all parts of the world that suited it. It hunted out the other higher races which were in a condition to dispute with it for enjoyment of the world's productions, and drove them to take refuge in such places as it did not desire to occupy. It checked the increase of the races nearest itself, and kept them exiled in woods and desert places, so that their further development was arrested, while itself, able to spread in all directions, to multiply without opposition, and to lead a social life, it developed new requirements one after another, which urged it to industrial pursuits, and gradually perfected its capabilities. Eventually this pre-eminent race, having acquired absolute supremacy, came to be widely different from even the most perfect of the lower animals. "Certain apes approach man more nearly than any other animal approaches him; nevertheless, they are far inferior to him, both in bodily and mental capacity. Some of them frequently stand upright, but as they do not habitually maintain this attitude, their organization has not been sufficiently modified to prevent it from being irksome to them to stand for long together. They fall on all fours immediately at the approach of danger. This reveals their true origin.[317] "But is the upright position altogether natural, even to man? He uses it in moving from place to place, but still standing is a fatiguing position, and one which can only be maintained for a limited time, and by the aid of muscular contraction. The vertebrate column does not pass through the axis of the head so as to maintain it in like equilibrium with other limbs. The head, chest, stomach, and intestines weigh almost entirely on the anterior part of the vertebrate column, and this column itself is placed obliquely, so that, as M. Richerand has observed, continual watchfulness and muscular exertion are necessary to avoid the falls towards which the weight and disposition of our parts are continually inclining us. 'Children,' he remarks, 'have a constant tendency to assume the position of quadrupeds.'"[318]