But this is not all: the great power of association possessed by man, together with his faculty of generalization and of speech, makes it possible for him to _learn_ his rôle in the community, instead of being born with it as are the bee and the ant. Great educability instead of differentiated instinct, infinite possibility, at the expense of the pains of learning, instead of an effortless but limited stock of inborn modes of behaviour--in this again man represents a qualitatively new organic type. By this means he can escape what has always been a necessity with lower forms: by means of education and machinery he can play a specialized part in the community life, and so build up a community with a high degree of division of labour, without being born specialized. He could not thus learn his rôle if he were not educable, nor if he could not manufacture tools. An ant or a duck or a dog possesses admirable tools for its particular job: but they are living parts of the organism’s own body. A worker ant cannot lay down its serviceable carpentering mandibles and become a soldier by picking up a large and warlike pair:--once a worker, always a worker; once a soldier, always a soldier--that is the rule for ants, but not for men. The efficiency and biological success of communities depends on the degree and accuracy of the division of labour and co-ordination between the units of which they are built up. This is true of cell-communities and the second-grade individuals or metazoa or multicellular animals and plants to which they give rise,[22] and also of the communities of metazoa and the third-grade individuals to which they give rise, whether the members of such communities of higher grade are physically bound together, as in a Hydroid or a Portuguese Man-o’-War, or united only by mental bonds, as are the communities of ants and bees and termites. As we have seen, the individuals are differentiated structurally for the different functions which they have to perform. This is not so in human species: a man is not born cross-legged to be a tailor, or broad-thumbed to be a miller, or big-armed to be a blacksmith. Even in the hereditary castes of India, the trade or profession is determined by tradition, and not by inborn structural adaptations. Still another consequence flows from this educability, this flexible and elastic mental organization. A man can pass from one occupation to another. He can be specialized for several, or combine a high degree of professional skill in one with the generalized knowledge of an amateur in another. It is this obvious but fundamental fact which is at the bottom of many of the failures to apply biological ideas to sociology.