It will harmonize with no dogma of theology, and no doctrine of science, to assume that these equine forms, separated by such enormous epochs of time, were specially created: all accurate knowledge forbids the supposition; while varieties sufficiently marked, such as the race-horse, the giant and powerful dray-horse, the Shetland and the Norman ponies, known to be derived from a common parentage, give the clearest sanction to the inference, that what we now know of the geological history of the horse proves it to be a product of the Darwinian law of evolution; that there has been no total destruction of equine (or any other) life in the great past; but that there has been a continuity of it, borne from region to region, and modified continuously by a thousand changing circumstances. Consequently we find, in the rocky records of the past, that organic types become simpler, and liker to each other, as we trace them through the incomplete geological record to a dim and far off age.
Here, then, we have a series of such generalized types, plainly related to each other in time, leading us down from the horse of historic times to less and less specialized forms of it, as the epoch grows more remote; until in the upper mesozoic or lower eocene beds, we find the progenitor of the line of the equine types we know, to be an animal with a splay foot of five toes, adapted to slow movement in a boggy soil. The slow specialization adapted it to increasing rapidity and ease of movement, and modified states of soil; acting, without doubt, as an increasing protection against its enemies, and providing it with an ever surer means of obtaining abundant and suitable food. And beneficial variation continued to act until the noble horse, beautiful in form, exquisitely graceful in action, and swift as the wind, had been thus created.
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]
A study of the Desmids, the Diatoms, the Radiolaria, or the Foraminifera amongst minute organisms will show that variations are so constant and so numerous, that the determination of what is called species, is difficult, and at times, impossible.
Who does not know of the varieties that are annually produced from seed-growths of favourite flowering plants?—the pelargonium, the primula, the viola, the rose, and hundreds of others.
That this is not confined to forms under cultivation is equally manifest. Common observation has not noted it perhaps, but there are no fewer than thirteen distinct forms of the common bramble or blackberry, with stem, flower, and fruit sufficiently varied to have induced some botanists to consider them species. Although each when seen is called by the majority of people ‘the wild rose,’ there are at the very least seventeen natural varieties. ‘Artificial selection’ has had no part in these variations and a thousand others that might be named.
Consider the variations constantly arising in fowls, canaries, dogs, and cattle. No litter of kittens is ever precisely alike, or precisely like either parent; and this is true even in human families.
Variation, then, is constant and universal; it acts in all directions and in every living thing. If, amidst the exigencies of the history of an organism, some variation in the progeny is beneficial in altered circumstances, it is by the very nature of things preserved. The offspring of all living organisms are greatly in excess of the number that can reach maturity; and with variations in every organism, and in every part of their organization, for ever occurring; and environments, during great cycles of time, undergoing constant and enormous changes; it is palpable that successive modifications must arise, and through all the countless ages of the past have arisen: resulting always in the ‘survival of the fittest’ or ‘natural selection,’ which ‘signifies the preservation of favourable individual differences and variations, and the destruction of those which are injurious.’[33] This is palpable, for individuals possessed of advantage over others must have the best chance of surviving and multiplying their kind; hence arise ‘varieties,’ ‘races,’ and ‘species;’ and if the enormous age of the period of life upon the globe, and the vicissitudes through which it has passed, be taken into account, it is impossible for a biologist to withhold consent to the fact that a ‘law,’ a method, has been demonstrated, which has been a certain and powerful factor, in producing the variety of the flora and fauna that have filled the earth, from the dawn of life upon the globe, up to the extant animals and vegetables which are the latest outcome of this great law. This is the conviction of all the experts of the world.
That there are other factors of evolution not yet discovered is almost inevitable; they, however, will be but added ‘laws;’ supplementary and co-ordinated methods—giving greater completeness to our knowledge of the origin of species.