There are from four thousand to six thousand living languages. The number of unspoken languages is not known. Their growth has required ages, and during their development many a parent stalk has ceased to exist. The changes in a language are slowly produced. It requires centuries to so far leave a language as to need an interpreter in order to understand it. Some idea of this slow change may be gained by comparing the writings in the English language of different periods. In the year 1362 appeared a poem called "Piers Ploughman's Creed," which begins as follows: "In a summer season, When soft was the sun, I shoop me into shrowds[108] As I a sheep[109] were; In habit as an hermit Unholy of werkes, Went wide in this world Wonders to hear; Ac[110] on a May morwening On Malvern hills Me befel a ferly,[111] Of fairy me thought." Etc. Written language is more permanent than spoken, but the process of either is necessarily slow. When it is remembered that a language has been derived successively through numerous others, no special limit or time can be given, although a very long period would be required. The usually accepted chronology would not allow sufficient time for the diversity in the Semitic family, to say nothing of the time required for the development of the three general classes. CHAPTER XVII. UNITY OF THE HUMAN RACE. The theory of the unity of the human race has caused a clash of opinions among men of science. It has been the great battle field among anthropologists, ethnologists, geologists, philologists, and theologists. Men of acknowledged ability have been arrayed on either side. Among the foremost in favor of a diversity of origin have been Agassiz, Sir Roderick I. Murchison, Georges Pouchet, A. R. Wallace, and Schleicher. But the weight of evidence and authority is most in favor of the unity of the human race. The advocates of the theory of the diversity of the origin of the human race have advanced many objections against the unity, and produced arguments in favor of their opinions. These may be summed up under five heads. 1. The anatomical differences between the different races, and especially those which distinguish the black and white. 2. The separation of the races from each other for unknown ages by great oceans, and by formidable and almost impassable continental barriers. 3. The disparity in intelligence, and the grades in civilization. 4. A medium type cannot exist by itself, except on the condition of being supported by the two creating types. 5. When two types become united, two phenomena may arise: _a_, Either one of them will absorb the other; or _b_, They may subsist simultaneously in the midst of a greater or less number of hybrids.