Self-motion, however, necesarily implies an intelligence and vice versa. One of these factors without the other is absolutely useless. Only in combination do they become a weapon in the struggle for lite. The power of self-movement is completely useless when it is not combined with a power to recognise the world in which I have to move myself. What use would the legs be to the stag if he had not the power to recognise his enemies and his feeding places? On the other hand, for a plant intelligence of any kind would be useless. Were the blade of grass able to see, hear or smell the approaching cow that would not in the least help it to avoid being eaten.
Self-movement and intelligence thus necessarily go together, one without the other is useless. Wherever these faculties may spring from, they invariably come up together and develop themselves jointly. There is no self-movement without intelligence, and no intelligence without self-movement. And together they serve the same ends: the securing and alleviation of the individual existence.
As a means to that they and their organs are developed and perfected by the struggle for life, but only as a means thereto. Even the most highly-developed intelligence has no capacities which would not be of use as weapons in the struggle for existence. Thus is explained the onesidedness and the peculiarity of our intelligence.
To recognise things in themselves may appear to many philosophers an important task; for our existence it is highly indifferent, whatever we have to understand by the theory in itself. On the other hand, for every being endowed with power of movement it is of the greatest importance to rightly distinguish the things and to recognise their relations to one another. The sharper his intelligence in this respect the better service will it do him. For the existence of the singing bird it is quite indifferent what those things may be in themselves which appear to it as berries, hawks, or a thunder-cloud. But indispensable is it for its existence to distinguish exactly berries, hawks, and clouds
