Associated in a special way with his great brain are his organs of speech and manipulation. These three structures, the brain, the vocal apparatus, and the hand, undoubtedly underwent concurrent evolution by the constant survival, during a period of intense competition, of those individuals who were naturally the best capable of receiving and storing experience, of using it for the intelligent manipulation of objects, and of communicating it to their fellows and descendants through the medium of speech. Even the highest of the lower animals are able to learn from one another only by example or through such very elementary verbal signs as calls, growls, or cries of alarm, which express no more than simple emotions. Their traditional knowledge, therefore, is as nothing compared with that of man, who by means of articulated speech communicates not only information concerning sense impressions and emotions, but complex items of knowledge and processes of thought which have been garnered, elaborated, and systematised during tens of thousands of years by millions of predecessors. Without speech, or some such method of communicating abstruse information, his great brain would be useless. But knowledge and powers of thought are of no avail unless they can be translated into action; and for this the hands are necessary. To set free the fore limbs, which had hitherto been organs of locomotion, for their new function of manipulation, man became a biped, and assumed the erect posture--by no conscious effort, however, but solely by the survival of the fittest in each generation. [Sidenote: Man Paves His Way to Greatness] Savage man, then, differs from the lower animals in that he has a larger brain, a more capacious memory, and greater powers of utilising and communicating its contents. Modern man differs from ancient man because he is the heir of longer experience. Civilised man differs from the savage chiefly in that he has invented and more or less perfected certain artificial aids to speech, written symbols by means of which he is able to store in an available form knowledge immensely more abstruse and voluminous than would otherwise be possible. His books are artificial memories and vehicles of communication of unlimited capacity and unerring accuracy. Moreover, by means of these symbols he is able, as in the mathematics, to perform feats of thinking quite beyond the powers of his unaided mind; just as by means of machinery and other mechanical contrivances he is able to perform physical feats beyond the unaided powers of his body.