Are races, then, brave or cowardly, energetic or slothful, enlightened or savage, and so forth, by nature or by training? Are the qualities that have enabled some races to flourish, while others are decadent, transmitted as instincts or handed on, as knowledge is? The reader has now materials of a kind not usually found in historical works on which to found a judgment. He must bear in mind that, while an American infant reared by cannibals would retain the bodily characteristics of his race mentally, he could not be other than a savage. He must remember also that some races have altered their mental characteristics very rapidly. Thus, in the fifteenth and sixteenth centuries, immediately after the long Dark Ages, the British and several other European races suddenly became intellectually active and socially progressive. The Japanese supply a more modern, the Greeks and Romans more ancient, instances. The latter quite as suddenly sank into abysmal degradation. Innate mental characters, such as the instincts, usually change so slowly that not merely historical but geological time elapses before the alteration is perceptible. Again, the reader must note that, while the _opinion_ that racial traits are inborn is nearly universal, most men _act_ as if they knew them to be acquired; for nearly all men are careful in training their children, especially with respect to those traits that contribute to the formation of character. [Sidenote: Great Facts to Remember] Doubtless, races of men differ innately in mind as they do in body, but these differences can occur only within narrow limits. The instincts of all races are, of course, very similar, for all the instincts are essential to the preservation of life. But races may differ in strength of instinct, and more especially in powers of memory. Thus it is possible, or probable, that the English, for example, are more capable of profiting by experience than Australian blacks. Certainly, their brains are larger. On the other hand, the brain grows under the stimulus of use, and therefore the larger size of the English brain may be due to more arduous labour. [Sidenote: The Real Value of History]