after it had once made its appearance, became a controlling factor in the development of the machine.  It must not be understood by this that animals have had any consciousness of the development of their body, or that they have made any conscious endeavours to modify its development.  This has not always been understood.  It has been frequently supposed that the claim that consciousness has an influence upon the development of an animal means that the animal has made conscious efforts to develop in certain directions.  For example, it has been suggested that the tiger, conscious of the advantage of being striped, had a desire to possess stripes, and the desire caused their appearance.  This is absurd.  Consciousness has been a factor in the development of the machine, but an indirect one.  Consciousness leads to effort, and effort has a direct influence in development.  For example, an animal is conscious of hunger, and this leads to efforts on his part to obtain food.  His efforts to obtain food may lead to migration or to the adoption of new kinds of food or to conflicts with various kinds of rivals, and all of these efforts are potent factors in determining the direction of development.  Consciousness, again, may lead certain animals to take pleasure in each other’s society, or to recognize that in mutual association they have protection against common enemies.  Such a consciousness will give rise to social habits, and social habits are a very potent factor in determining the direction in which the inherited variations will tend; not, perhaps, because it effects the variations themselves, but rather because it determines which variations among the many shall be preserved and which rejected by natural selection.  Consciousness may lead the antelope to recognize that he has no chance in a combat with a lion, and this will induce him to flee.  The habit of flight would then develop the power of flight, not because the antelope desired such power, but because the animals with variations which gave increased power of flight would be the ones to escape the lion, while the slower ones would die without offspring.  Thus consciousness would indirectly, though not directly, result in the lengthening of the legs of the animal and in the strengthening of his running muscles.  Beyond a doubt this factor of consciousness has been a factor of no little moment in the development of the higher types of organic machines.  We can as yet only dimly understand its action, but it must hereafter be counted as one of the influences in the evolution of the living machine.

But, after all, these are only questions of the method of the action of certain well demonstrated, fundamental factors.  Whether by natural selection, or by the inheritance of acquired characters produced by the environment, or whether by the effect of isolation of groups of individuals, the machine building has always been produced in the same way.  A machine, either through the direct influence of the environment,