But the main interest is in the tapir's snout, which, like the elephant's trunk, has wonderful powers of holding and tearing down branches, of feeling, sensing, and handling. The horse-ancestor had a tapir snout of which the horse's upper lip is the survival. Play with any horse and you will notice how the lips try to curl round and grip one's fingers, to bring them within reach of the teeth. They will curl round, grip, and tear the bunch grass or pampas grass of the wild ranges. They are softer than velvet, delicate as a baby's hand, sensitive as the fingers of an artist, will caress like a woman's lips. The short hairs have an exquisite sense of touch, the beard bristles {7} are used to sense grass with in the dark, and the whole instrument is wondrously designed to select sweet grasses, rejecting poisonous or unwholesome plants, so that feeding goes on through hours of total darkness. {Sidenote: The earlier world] Had the Earth remained an unbroken forest under a roof of cloud there had been no change since the Age of Dragons, no mighty drama of Creation lifting man and horse out of the shadows to work together as master and servant in the conquest and taming of the wilderness and final subjugation of the World. The one great factor in Earth's history is the lessening of the sun's heat. Through long revolving ages the heat which the Earth received from the sun diminished. Ever less vapour was lifted from the Equatorial seas, the world-roof of cloud thinned out and disappeared; direct sunshine poured down instead of the endless rains; there was no moisture left to nourish the worldwide forest. Little by little glades opened in the woodlands caused by drought, savannahs replaced the timber, of tall jungle grasses, the openings widened into prairies, and vast grassy steppes, thousands of miles in breadth, evolved at their centres an aching core of desert. So we have reached the phase when forest, prairie {8} and desert each claim one-third of the land surface. We are passing on to the phase, which Mars has reached, of world-wide desert, and beyond that is the far future when, like the Moon, our Earth will swing dead through the great deeps of space. [Sidenote: The changing climate]