This general notion, however, must not be allowed to prevent us from admitting that among sundry tribes of mankind the images may be historical. This is asserted with regard to the Bongos by Schweinfurth, and with regard to the Gold Coast negroes by Cruickshank. The wooden effigies on the Marquesas Islands are described by Herr Schmeltz as “constructed in memory of celebrated members of the tribe.”[243] The Melanesian sculptures also, according to Codrington, are chiefly commemorative. It must be observed, however, that according to his own description a sort of religious respect is paid at least to some of them.[244] More undeniably commemorative examples are to be found in New Zealand. Although no attempt to reproduce likenesses is made in these colossal wooden statues, they nevertheless more nearly approach the idea of monumental commemorative portraiture than any similar works of primitive art. The patterns of tattooing, that infallible means of identification amongst the Maoris, render it possible to preserve the memories of the individual ancestors through pictorial representation.[245] Not less problematic than ancestral sculptures are the much-debated rock-paintings and engravings that can be found in every part of the world. Herr Andree finds a sort of learned bias in the general tendency to look for some serious, sacred, or historical meaning in every petroglyph. He points, very sensibly as it seems, to the prevailing impulse of the idle hand to scratch some figures, however meaningless, on every inviting and empty surface. Especially at much frequented localities—such as meeting-places, common thoroughfares, and places of rest for travellers—where the drawings of previous visitors call for imitation, this temptation must be looked upon as a very strong one.[246] There is no reason for regarding the savage and the prehistoric man as devoid of an impulse, which, as we all know, shows its strength among the very lowest and most primitive layers of civilised society. It is unnecessary, therefore, to find anything more remarkable in the petroglyphs than is to be found in the familiar pictures on walls, trees, and rocks which have been wantonly decorated by the modern vandal. This common-sense explanation is undoubtedly sufficient to account for the origin of many much-debated works of glyphic art. But however sound within its proper limits it cannot be extended so as to give a general solution of the petroglyph problem. It is not likely, as Mr. Im Thurn observes, that pictures such as the rock-engravings in Guiana, to produce which must have cost so much time and trouble, should have their origin in mere caprice and idleness.[247]