"Looking back through the prodigious vista of the past I find no record of the commencement of life, and therefore I am devoid of any means of forming a definite conclusion as to the conditions of its appearance. Belief, in the scientific sense of the word, is a serious matter, and needs strong foundations. To say, therefore, in the admitted absence of evidence, that I have any belief as to the mode in which the existing forms of life have originated, would be using words in a wrong sense. But expectation is permissible where belief is not; and if it were given me to look beyond the abyss of geologically recorded time to the still more remote period when the earth was passing through physical and chemical conditions which it can no more see again than a man can recall his infancy, I should expect to be a witness of the evolution of living protoplasm from non-living matter. I should expect to see it appear under forms of great simplicity, endowed, like existing fungi, with the power of determining the formation of new protoplasm from such matters as ammonium carbonates, oxalates, and tartrates, alkaline and earthy phosphates, and water, without the aid of light. That is the expectation to which analogical reasoning leads me, but I beg you once more to recollect that I have no right to call my opinion anything but an act of philosophical faith."
Since these words were written the reasons for Huxley's "philosophic faith" have been strengthened by later discoveries, and perhaps a majority of biologists would take the view that except for practical purposes there is no sound reason for placing living and inorganic aggregations of matter in totally different categories. But even if the main outline of the theory of evolution were proved beyond the possibility of doubt, if we could trace existing plants and animals backwards with the accuracy of a genealogist and find that they had been developed, under purely physical "laws" from a few simple forms, and if we could understand exactly how these few simple forms of living matter took origin from non-living matter, we would not, if we followed Huxley, be able to rest in a purely materialistic position. As he, in different words, repeatedly said: