In all this personification of physical phenomena our prehistoric ancestors were greatly assisted by that theory of ghosts which was perhaps the earliest speculative effort of the human mind. Travellers have now and then reported the existence of races of men quite destitute of religion, or of what the observer has learned to recognize as religion; but no one has ever discovered a race of men devoid of a belief in ghosts. The mass of crude inference which makes up the savage's philosophy of nature is largely based upon the hypothesis that every man has _another self_, a double, or wraith, or ghost. This "hypothesis of the _other self_, which serves to account for the savage's wanderings during sleep in strange lands and among strange people, serves also to account for the presence in his dreams of parents, comrades, or enemies, known to be dead and buried. The other self of the dreamer meets and converses with the other selves of his dead brethren, joins with them in the hunt, or sits down with them to the wild cannibal banquet. Thus arises the belief in an ever-present world of ghosts, a belief which the entire experience of uncivilized man goes to strengthen and expand."[5] Countless tales and superstitions of savage races show that the hypothesis of the other self is used to explain the phenomena of hysteria and epilepsy, of shadows, of echoes, and even of the reflection of face and gestures in still water. It is not only men, moreover, who are provided with other selves. Dumb beasts and plants, stone hatchets and arrows, articles of clothing and food, all have their ghosts;[6] and when the dead chief is buried, his wives and servants, his dogs and horses, are slain to keep him company, and weapons and trinkets are placed in his tomb to be used in the spirit-land. Burial-places of primitive men, ages before the dawn of history, bear testimony to the immense antiquity of this savage philosophy. From this wholesale belief in ghosts to the interpretation of the wind or the lightning as a person animated by an indwelling soul and endowed with quasi-human passions and purposes, the step is not a long one. The latter notion grows almost inevitably out of the former, so that all races of men without exception have entertained it. That the mighty power which uproots trees and drives the storm-clouds across the sky should resemble a human soul is to the savage an unavoidable inference. "If the fire burns down his hut, it is because the fire is a person with a soul, and is angry with him, and needs to be coaxed into a kindlier mood by means of prayer or sacrifice." He has no alternative but to regard fire-soul as something akin to human-soul; his philosophy makes no distinction between the human ghost and the elemental demon or deity.