ment than did his lost powers. His acquired habit of bi-pedal progression, a habit acquired anew by every individual, has resulted in immense and obvious structural changes. But certainly, above all other acquired traits, his acquired trait of speech has most influenced his survival rate, and has therefore been the cause of the most far-reaching evolution and retrogression. To this acquired trait very much of the evolution and retrogression directly traceable to other acquired traits is indirectly traceable. By means of it, more than by means of any other of his acquired traits, has he been placed in harmony with the environment. For it is clear, that those individuals who had the best powers of speech, i.e. of communicating information, and the best powers of understanding speech, i.e. of acquiring information, had the best powers of placing themselves in harmony with the environment. Owing to the acquirement by generation after generation through innumerable generations of language, man has retrogressed so far in structure and instincts that, but for speech, and all that is communicated by one generation to another through the medium of speech, he is as certainly unfit for existence as F. rufescens is without its slaves. If for a single generation this all-important trait were not acquired, and man, were it possible, survived, he would at once be reduced to the condition of a brute, and, his equipment of instinct being small, a very helpless brute. His highest faculty, his enormous power of varying mentally in response to stimulation, of acquiring fit mental traits, would be rendered nugatory, since it would no longer receive appropriate stimulation. Under the new condition of things, the fit who survived would no longer be the same as heretofore, and since the power of acquiring the higher mental traits would no longer be a principal factor in survival, that power would necessarily decline
