Now the most absolutely assured, the most universally accepted truth within the whole realm of human knowledge and experience is the immutability of nature’s laws; and the certainty that their action has been ‘established for ever’ through all space and all time. Great as was the knowledge of ancient and classic peoples, that of which they knew relatively least, was nature. This arose from their inability to perceive the inexpressible vastness of nature, on the one hand, and the detailed constitution of the earth and its universal flora and fauna, on the other. The obvious inference as to the origin of the universe, as they knew it, was, that all that constituted the world and its occupants and inhabitants, mineral, vegetable, and animal, were individual direct creations. But, knowing as we now know, the immutability and universality of the laws of nature, in relation equally to the organic and living as to the inorganic and not-living, and knowing as we do the geological and palæontological history of the earth, and the nature and characteristics of its living inhabitants, it is as manifest as the axioms of geometry, that the direct and supra-natural creation of new species, or even new genera, is absolutely untenable. Now modern biological science, guided by the splendid genius and ceaseless research of Darwin, and the whole field of biologists, for the past quarter of a century, has been able for all practical purposes to discover and demonstrate a great ‘law’ or method, according to which all the varieties of living ‘species,’ animal and vegetable, have arisen; connecting the remotest ages of the life of the globe with the present flora and fauna in one unbroken continuity, by one unchanging method. The organic history of any individual becomes an analogue of the organic history of the world. The individual begins existence as a minute ovum, and progresses to completeness. The vast series of organic forms, fossil and extant, began in one or more ‘primordial germs.’ The law of all living things, and especially the lowliest, is rapid and abundant reproduction. Variations in individuals so reproduced are as absolutely universal as reproduction itself. It does not require the accurate knowledge of the botanist or the zoologist to discover this. A careful study of any group of living forms, lowly or highly organized, will make this palpable to any observer. The septic organisms, for example, which arise from germs (not those which arise from self-division) constantly vary; and I have been able to make use of this tendency so as to enable three of these wonderful organic and vital specks to slowly change, so as to adapt themselves to changed environments, until, in the course of years, from normally living at a temperature of 60° Fahr. they lived at last, and multiplied enormously, at a temperature of 157° Fahr.; and in the slow process of adaptation, demonstrated fundamental changes were undergone by the organisms.[32]