Schopenhauer warns us against substituting this philosophical explanation for scientific aetiology. The chain of causes and effects, he points out, is not broken by the differences of the original, irreducible forces. The aetiology and the philosophy of nature go side by side, regarding the same object from different points of view. Yet he also gives us in relation to his philosophy much that is not unsuggestive scientifically. His doctrine is not properly evolutionary, since the Ideas are eternal; but he has guarded incidentally against our supposing that all the natural kinds that manifest the Ideas phenomenally must be always represented in every world. For our particular world, comprising the sun and planets of the solar system, he sets forth in the _Parerga_ an account of the process by which it develops from the nebula to man. This was referred to in the preceding chapter. In his fundamental work he describes a struggle, present through the whole of nature, in which the phenomenal manifestations of the higher Ideas conquer and subjugate those of the lower, though they leave them still existent and ever striving to get loose. Here has been seen an adumbration of natural selection: he himself admits the difficulty he has in making it clear. We must remember that it is pre-Darwinian. Knowledge or intelligence he seeks to explain as an aid to the individual organism in its struggle to subsist and to propagate its kind. It first appears in animal life. It is represented by the brain or a large ganglion, as every endeavour of the Will in its self-objectivation is represented by some organ; that is, displays itself for presentation as such and such an appearance. Superinduced along with this contrivance for aid in the struggle, the world as presentation, with all its forms, subject and object, time, space, plurality and causality, is all at once there. 'Hitherto only will, it is now at the same time presentation, object of the knowing subject.' Then in man, as a higher power beyond merely intuitive intelligence, appears reason as the power of abstract conception. For the most part, rational as well as intuitive knowledge, evolved originally as a mere means to higher objectivation of the Will, remains wholly in its service. How, in exceptional cases, intellect emancipates itself, will be discussed under the heads of AEsthetics and Ethics.