In the first place, he is capable of speech, and possesses a true language--not a mere repertory of sounds or signs associated with different states of mind, as in some higher organisms, but a language comprising special symbols for particular external objects, and thus making it possible to have a much more detailed knowledge and classification of the outer world. In the second place, he can frame abstract ideas or concepts, and is thus enabled to extract the general kernel from the husk of innumerable separate and different particulars. As a result of these two faculties, he possesses what we may call a new, accessory form of inheritance. True biological inheritance takes place by means of the reproductive cells. In some birds and mammals, the behaviour of the young is modified by what they learn from their parents, so that they profit by the experience of their elders; however, this profiting by experience is not cumulative, but must be repeated afresh in each generation. In man, on the other hand, speech and writing make it possible to construct a continuous tradition, by means of which experience may be actually accumulated from generation to generation. There are thus two forms of inheritance in man, two hereditary streams--biological inheritance, by means of germ-cells or detached portions of the organism, in which favourable mutations may be accumulated by selection, and “experience-inheritance,” by means of tradition, in which useful experience may be accumulated by the activity of mind. By means of tradition-inheritance, man is virtually enabled to “inherit acquired characters”; thus the environment in which the latter stages of his development are passed through, and consequently his adult self, the end-product of that development, can be altered far more rapidly than in any other organism. Finally, it is possible, as is being increasingly realized, thus to accumulate experience relating to the alteration of biological inheritance, and so eventually to substitute conscious purpose for blind natural selection in man’s future evolution.