CHAPTER III.

NATURE'S EVIDENCE OF THE LAW OF LIFE AND GROWTH.

HE preamble constituting the last chapter was necessary,

THE lest the reader might not realize the intimate relation

which the law of development bears to every passing incident of life. The evidence adduced by Darwin, Wallace, Spencer, and many others, in support of the alleged existence of the law, resolves itself in a general way into the categories of former geological change and the comparison of living with extinct forms of life, as known through living creatures and fossil remains. This chapter will be especially devoted to exhibiting some of the evidence upon which the existence of the alleged law rests, coupled with such manifestly implied considerations as to the importance of its recognition in the conduct of daily life as will obviate the necessity of their formal presentation.

All the varieties of what we call fancy-pigeons-carriers, tumblers, pouters, fan-tails, turbits, and others-are derived from the rock-pigeon, which is blue with black-barred wings. This has been proved by breeding those pigeons together in such a manner as to produce partial reversion to the assumed parent stock.

The results of the breeding of domesticated animals show that horses, cattle, sheep, and dogs can be so changed within their kind as to be hardly recognizable as derived from the animals which formed the point of departure. The same thing holds good of plants. The effect described is manifestly accomplished through artificial selection, as distinguished from natural selection, but this throws great light upon the question of natural selection. Artificial selection itself is naturally divided into two classes,-conscious and unconscious.

The selection is unconscious when, as often happens, a

person, not a breeder of animals or a cultivator of plants, effects a change by selection in either, without any remote ulterior object. Putting, for the sake of simplicity, plants out of consideration, and confining ourselves, as heretofore, to animals, the case referred to is illustrated by the occasional action of a person breeding, for the assumed improvement of certain qualities, from a pair of individuals which happen to please him by their traits. The selection, on the contrary, is conscious when, as with skilled breeders, generation after generation of animals is bred for the finest points of physical and mental traits, representing generally useful qualities. Speed is thus developed in horses, milk-giving or butter-making qualities in cows, hunting qualities in some dogs, size and ferocity in others, speed or household qualities in others; the qualities in some of these latter being not at all useful, but fanciful, as are the peculiarities of the French poodle, the King Charles spaniel, and the pug. But, whether the quality be useful or useless, it is proved that any amount of divergence is seemingly producible from the parent stock. This pursuit, even during an ordinary human life, suffices to produce wonderful changes in domestic animals. When breeders thus, through conscious selection, have pursued the same object, that is, definite direction toward the object through several successive generations,-the gradually-accumulated differences make at last in the animal under development a transfiguring result. Imagine what could be produced in the way of divergence of animal forms if men had the power and will, through continuous living, to carry on their conscious selection indefinitely. Imagine, then, the effect, if nature has been applying through thousands of years, millions, æons, a rigid selection, through a universal law of growth, life, and death, imposed by the Creator. We see it all around us, in our own persons, and in the whole outlying world. The present is the growth of the past, linked through endless series to the creation.

When a genus, the last bounds within which classification places species, consists of very many species and varieties, it is found that, throughout, the likeness between many forms is very close, and, moreover, that, grouped around special forms, are congeries or clusters of species and varieties, more closely similar to each other than are to each other the species generally of the inclusive genus. This is a very striking fact, awakening suspicion that such species, constituting the genus, have been molded through similarity and dissimilarity of conditions found in an extensive range, and, further, so as to form under continued individual similar and dissimilar conditions, continuously derived varieties, all of which may eventually become true species.

Species which are most abundant in individuals, and at the same time are most widely diffused in a single country, being there what may be properly termed the dominant species, exhibit the most numerous varieties. This phenomenon points in the same direction as that which has just been noticed, and, moreover, confirms its ultimate suggestion to the mind. That is to say, if variation is producible and produced from any cause whatever, we cannot say that the same cause is incapable of producing indefinite change; we cannot say that species may not be produced from varieties, and that the final product in the course of ages may not be quite dissimilar from the stock from which observation has been supposed to begin. Therefore, if natural selection as defined can produce change, it is impossible mentally to limit the amount of change.

There is a singular and surprising relation between the similarities and dissimilarities among animals found on continents and on the neighboring islands, and striking relations among animals inhabiting the islands themselves, pointing to primary differentiation as between the continental and insular forms and secondary differentiation as among the insular forms.

It has been ascertained, too, that in large areas which, there is reason to believe, from geological evidence, have not been subjected to invasion of new forms for many ages, the living and fossil forms make a much closer series than they do in those regions which geological evidence shows to have been open for long periods to the invasion of species. The most marked exemplifications of this circumstance are exhibited by the persistence in Australia of the marsupial (pouched) type of animal, such as the kangaroo, and in South America of the edentata (sloth) type, like the armadillo, ant-eater, and others.

The stripes of the zebra are sometimes suggestively indicated on the horse and the ass. Similarly, spots appear and disappear on certain adult deer, only the young (the fawn) normally exhibiting them at present. These are believed to be cases of partial reversion to primitive characteristics, the common progenitor of the zebra, the horse, and the ass being supposed to have been some striped animal, and that of the deer tribe some spotted and otherwise widely different animal from the present deer.

There is a whole succession of animals graduating off into each other in functional adaptation of the eye, as they graduate in space from light to twilight and then to total darkness, the eye becoming of less and less efficiency and then of none at all,— in structure, only the rudiment of an eye. Is it to be supposed that these animals were separate creations for separate localities, each having been endowed, if it can be so termed, with structures which sometimes have little and sometimes no relation to use, merely to suggest an idea of symmetry and system in creation? Is it not rather to be supposed that in all of these creatures the shamness of seeing could not be the result of special creation, but that their eyes once exercised more function than the least imperfect of them now? that, in the course of time, loss of function, through changed conditions and habits, led to partial loss of structure? and that the present structures, which,

when otherwise, once served a purpose, might, under changed conditions, serve again the once discontinued purpose?

The blind fish of the Mammoth Cave of Kentucky are the most familiar instance of the rudimentary condition of the eye to which reference has just been made, and crabs there have the foot-stalks for eyes, without the eyes themselves. Rudimentary organs, however, extend over an immense range among living things. The pouch of the marsupial is really the first form by which the breast of land mammals is foreshadowed. In the case of the male sex among mankind, physiologists are agreed that the breast can hardly be regarded as rudimentary, its glands, in certain cases, being known to secrete milk. It is therefore regarded simply as an organ which is no longer normally capable of function. Minute anatomical examination of the body, known as histology, shows that, even in so remarkable a connection as that between the human spine and brain, there is a demonstrable case near the upper vertebræ, where the fibres still exist, but are functionless. In this part, therefore, they have been superseded by other special adaptations, and in the course of ages may become more and more rudimentary, and perhaps finally disappear.

There are upland geese with webbed feet. What possible use can webbed feet now be to these geese? Darwin remarks of the frigate-bird, or man-of-war hawk, as often called in Florida, that it has all its toes webbed, and that no one but Audubon ever saw it alight on the surface of the ocean. We can personally confirm this statement, having watched the beautiful floating of thousands of these birds in their solitary flight through the air, soaring in concentric circles on apparently motionless pinions. It is not uncommon for any bird which obtains food from the water to flutter immediately over the surface, seizing what it can peck up or grasp; and this produces the effect which, doubtless, Audubon perceived when he suspected that the webbed feet of the frigate-bird aided it to support itself upon