“Still another consideration seems to me the most interesting of all, and yet I have never seen it clearly expressed elsewhere. It is, in a sense a validation of the ‘animal faith’ given by Russell (after Santayana) … as sole basis for assuming that we really can obtain knowledge of the outer world. The fact is that man originated by a slow process of evolution guided by natural selection. At every stage in this long progression our ancestors necessarily had adaptive reactions to the world around them. As behavior and sense organs became more complex, perception of sensations from those organs obviously maintained a realistic relationship to the environment. To put it crudely but graphically, the monkey who did not have a realistic perception of the tree branch he jumped for was soon a dead monkey-and therefore did not become one of our ancestors. Our perceptions do give true, even though not complete, representations of the outer world because that was and is a biological necessity.”