Instead of elaborating on accepted principles, let us simply point out that for the last hundred years the natural sciences have abandoned completely… - Santiago Ramón y Cajal

Now and then philosophers invade the field of biological sciences with these beguiling generalizations, which tend to be unproductive, purely verbal solutions lacking in substance. At best, they may prove useful when viewed simply as working hypotheses.

There is no doubt that the human mind is fundamentally incapable of solving these formidable problems (the origin of life, nature of matter, origin of movement, and appearance of consciousness). Our brain is an organ of action that is directed toward practical tasks; it does not appear to have been built for discovering the ultimate causes of things, but rather for determining their immediate causes and invariant relationships.

In summary, there are no small problems. Problems that appear small are large problems that are not understood (p. 17).