But a too rigid application of biological principles lands one in error. Society is more than a mere biological group, and no reasoning that proceeds on the assumption that it is no more than that can avoid confusion. And we certainly cannot square the facts with a theory which treats the human organism as passive under the operation of environmental forces. The conviction that man plays a positive part in life is general, powerful, and, I think, justifiable. But if what _I_ do is at any time the product of the environmental forces, physical and other, there does not seem any room for _me_ as an active participant. And the facts seem to demand that the individual should appear in some capacity other than that of representing the total in an environmental calculation. This would leave man with no other function than that of a billiard ball pushed over a table by rival players. Given the force exerted by the player, added to the size, weight, and position of the ball, and the product of the combination gives us the correct answer. But this kind of calculation will not do in the case of man. Here we must allow, in addition to external influences, the positive action of man on his surroundings. The conception of the organism as a plexus of forces capable of this reaction is, indeed, vital to our conception of a living being. Granted that in either case, that of the billiard ball and that of the man, the result expresses the exact sum of all the forces aiding at the time, there still remains an important distinction in the two cases. Whether the billiard ball is struck by a professional player or by an amateur, provided it be struck in a particular way the result is in both cases identical. An identity of result is produced by an identity of external conditions. With the human organism--with, in fact, any organism--this rule does not apply. In any two cases the external factors may be identical, but the results may be entirely different. A temptation that leaves one unaffected may prove overpowering with another. Exactly the same conditions of food, occupation, residence, and social position may co-exist with entirely different effects on the organism. These differences will be manifested from the earliest years and are a direct consequence of the positive reaction of the organism on its environment, a reaction that is more profound in the case of man than in that of any other animal. To put the matter briefly. In the case of the billiard player the ball remains a constant factor in a problem in which external conditions represent a variant. In the case of man and his environment we are dealing with two sets of factors, neither of which is constant and one of which--the human one--varies enormously. And the reaction of man on his environment becomes so great as to result in its practical transformation.