Time is an important element in the formation of our domestic races, as it permits innumerable individuals to be born, and these when exposed to diversified conditions are rendered variable. Methodical selection has been occasionally practised from an ancient period to the present day, even by semi-civilised people, and during former times will have produced some effect. Unconscious selection will have been still more effective; for during a lengthened period the more valuable individual animals will occasionally have been saved, and the less valuable neglected. In the course, also, of time, different varieties, especially in the less civilised countries, will have been more or less modified through natural selection. It is generally believed, though on this head we have little or no evidence, that new characters in time become fixed; and after having long remained fixed it seems possible that under new conditions they might again be rendered variable. How great the lapse of time has been since man first domesticated animals and cultivated plants, we begin dimly to see. When the lake-buildings of Switzerland were inhabited during the Neolithic period, several animals were already domesticated and various plants cultivated. If we may judge from what we now see of the habits of savages, it is probable that the men of the earlier Stone period--when many great quadrupeds were living which are now extinct, and when the face of the country was widely different from what it now is--possessed at least some few domesticated animals, although their remains have not as yet been discovered. If the science of language can be trusted, the art of ploughing and sowing the land was followed, and the chief animals had been already domesticated, at an epoch so immensely remote, that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavonic languages had not as yet diverged from their common parent-tongue.[598] {244}