organic. Such changes, however, take place from time to time, either single, sudden, and violent, or numerous and unnoticed, the sum total and effect of which, however, equally brings on new situations, as, for example, alterations in the ocean currents, in the surface of the earth, perhaps even in the position of the planet in the universe, which bring about climatic changes, transform thick forests into deserts of sand, cover tropical landscapes with icebergs, and vice versa. These alterations render new adaptations to the changed conditions necessary; they produce migrations which likewise bring the organisms into new surroundings, and produce fresh struggles for life between the old inhabitants and the new incomers, exterminate the badlyadapted and the unadaptable individuals and types, and create new divisions of labour, new functions and new organs, or transform the old. It is not always the highest developed organisms which best assert themselves by this new adaptation. Every division of labour implies a certain one-sidedness. Highly-developed organs, which are specially adapted for a particular method of life, are for another far less useful than organs which are less developed, and in that particular method of life less effective, but more many-sided and more easily adaptable. Thus we see often higher-developed kinds of animals and plants die out, and lower kinds take over the further development of fresh higher organisms. Probably man is not sprung from the highest type of apes, the man-apes, which are tending to die out, but from a lower species of four-handed animals.
2.—Self-movement and Intelligence.
At an early period the organisms divided themselves into two great groups: those which developed the organs of self-motion, and those which lacked it; animals and plants. It is clear that the power of self-movement is a mighty weapon in the struggle for life. It enables it to follow its food, to avoid dangers, to bring its young into places where they will be best secured from danger, and which are best provided with food.
