Lamarck anticipated Lyell in supposing geological changes to have been due almost entirely to the continued operation of the causes which we observe daily at work in nature: thus he writes:-- "Every observer knows that the surface of the earth has changed; every valley has been exalted, the crooked has been made straight, and the rough places plain; not even is climate itself stable. Hence changed conditions; and these involve changed needs and habits of life; if such changes can give rise to modifications or developments, it is clear that every living body must vary, especially in its outward character, though the variation can only be perceptible after several generations. "It is not surprising then that so few living species should be represented in the geologic record. It is surprising rather that we should find any living species represented at all.[244] "Catastrophes have indeed been supposed, and they are an easy way of getting out of the difficulty; but unfortunately, they are not supported by evidence. Local catastrophes have undoubtedly occurred, as earthquakes and volcanic eruptions, of which the effects can be sufficiently seen; but why suppose any universal catastrophe, when the ordinary progress of nature suffices to account for the phenomena? Nature is never _brusque_. She proceeds slowly step by step, and this with occasional local catastrophes will remove all our difficulties."[245] In his fourth chapter Lamarck points out that animals move themselves, or parts of themselves, not through impulsion or movement communicated to them as from one billiard ball to another, but by reason of a cause which excites their irritability, which cause is within some animals and forms part of them, while it is wholly outside of others.[246] I should again warn the reader to be on his guard against the opinion that any animals can be said to live if they have no "inward motion" of their own which prompts them to act. We cannot call anything alive which moves only as wind and water may make it move, but without any impulse from within to execute the smallest action and without any capacity of feeling. Such a creature does not look sufficiently like the other things which we call alive; it should be first shown to us, so that we may make up our minds whether the facts concerning it have been truly stated, and if so, what it most resembles; we may then classify it accordingly. "Some animals change their place by creeping, some by walking, some by running or leaping; others again fly, while others live in the water and swim. "The origin of these different kinds of locomotion is to be found in the two great wants of animal life: 1, the means of procuring food; 2, the search after mates with a view to reproduction. "Since then the power of locomotion was a matter affecting their individual self-preservation, as well as that of their race, the existence of the want led to the means of its being gratified."[247]