"It is in proportion to our success or failure in conceiving facts simply that sciences are abstract or concrete, rational or descriptive. In these respects the contrast is great between the physical and the biological sciences. The figure of the earth, its path about the sun, and its relations to the other planets are readily conceivable in a first approximation as simple; but the forms of life seem complex, their activities manifold, and the concatenations interminable. Therefore, unlike celestial mechanics, the science of biology, which is the record of efforts accurately to describe and clearly to understand living things, is chiefly a science descriptive of concrete fact. It bears little resemblance to the more perfect science and as yet is in no danger of a relativist revolution. It has never attained, perhaps, as some have argued, it can never in any respect achieve and should not strive for the abstractness, the elegance, and the simplicity which are the mark of the classical epoch of many the physical sciences and the ideal of those who follow Newton and Willard Gibbs."