I do not propose to follow the example of many rather hasty philosophers and biologists, who have thought that, whenever the study of lower organisms permitted the promulgation of a biological law, such law can be lifted bodily from its context and be applied without modification to human affairs. Man is an organism--but a very exceptional and peculiar organism. Any biological law which epitomizes only facts about the lower creatures is not a general biological law, for general biological laws must take account not only of plants and animals, but of man as well. In practice, however, the simplest method is to frame our biological laws without considering man, and then to see in what way they must be modified if they are to be applied to him. Man differs biologically from other organisms in the following main ways. First, he has the power of thinking in concepts; in other words, his power of learning by experience is not always conditioned directly by the accidents of his own life, as is the case with animals endowed only with associative memory, but he can, by reaching the general from the special, attain to the possibility of dealing with many more, and more complicated, eventualities. Next, by means of speech, writing, and printing, he has developed a new mode of inheritance.[10] Each community, and indeed humanity as a whole, transmits its peculiarities to later ages by means of tradition, using that word in its largest sense. Physical inheritance of the same type as in all higher animals and plants is the necessary basis, but the distinctive characters of any civilization are based on this new tradition-inheritance. Thirdly, the type of mind which has been evolved in man is much more plastic--a much more elastic and flexible mechanism than any tool previously evolved by life for handling the problems of existence. As a consequence of this we have the substitution of general educability for specific instincts. For the power of performing comparatively few actions smoothly and without trouble, there is exchanged the possibility of a vastly increased range of action, but one which has to be learnt. As another consequence, man has come by the power--impossible to any other organism--of leading what is to all intents and purposes a multiple existence. It is for this very reason difficult to fit man into many of the ordinary biological categories. The physical and mental structure and the mode of life of even the highest of the animals are for all practical purposes a fixed quantity. An ant, for all its delicacy of adjustment, is little less than a sentient cog shaped to fit in just one way into the machinery of the community; a dog, for all his power of learning, is tied down and imprisoned within a rigidity and narrowness of bodily and mental organization difficult for us to imagine.