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 The child may learn to speak French, may acquire a new nationality or religion, may take to drink, may learn to gamble and swear. All these new acquisitions are "acquired characters." Among biologists the question whether such acquired characters can be transmitted has aroused the keenest controversy. On the whole there is a balance of authority for the view that no convincing evidence of their transmission has yet been forthcoming. We shall assume, in what follows, that this biological view is correct, i.e. that acquired characters are not transmitted.

§5. The Physical Environment. The environment is in some way or other the cause, or at least the occasion, of all the acquired characters which the individual develops. But it is more than that. The living creature owes its continued existence to its environment. The physical environment includes air, earth, light, heat, water, food, climate, scenery, and so on. From this environment all living beings, including man, derive nourishment and warmth, and without it life and growth would be impossible.

The tremendous importance of the direct influence of the physical environment on living creatures is most clearly seen in the case of plants and animals. Two or three illustrative points may be mentioned. (a) In some cases the environment exercises a regularly recurrent influence, and the living creature simply falls into step with it. For example, some kinds of tropical acacia have been so influenced by the regular alternation of a twelve-hours day and night, that they uniformly respond to it by opening