existed, which were exactly alike. This general class of facts has been designated by the term variation. Scientists hesitate, as well they may, to dignify variation by the name of law; for nothing could seemingly be more capricious in the manner of its occurrence, or more unaccountable, as regards any known law of causation.

Besides these slight variations of offspring from the type of the parents, there occasionally occur more marked variations, such as a supernumerary finger or toe. Of the same class are marked modifications of form and features, which occasionally make their appearance. A family is known to the writer, in which are several children with abnormally short and crooked limbs and a very peculiar cast of features,-in both respects entirely unlike either of the parents.

Now it is found that these unaccountable variations from the parent type usually descend to the offspring in the next and succeeding generations. A male child was born in the island of Malta, having on each hand six fingers including the thumb, and six toes on each foot. The family history of this individual has been traced down to his grandchildren inclusive. More than half of his descendants who were not fewinherited his peculiarity of hands and feet. In 1791 there was born in Massachusetts a male lamb with very short bow legs and a very long body. The owner sagaciously propagated from him a new breed of sheep, called the otter breed. The peculiar merit of the stock was freedom from the vice of jumping fences. Accordingly the breed was much sought after by farmers, and thus propagated extensively over the State. Many other similar facts might be adduced.

Thus we have, first, the law of inheritance, or the general normal tendency of the offspring to copy the type of the parents; secondly, the general fact of more or less deviation in the offspring from the similitude of the parents, with occasionally a variation so marked as to constitute a seeming breach of the law of inheritance; and thirdly, we have the law of inheritance taking up and perpetuating through succeeding generations, not only the slighter variations, but also

any seemingly abnormal type that may intrude upon the line of descent. It should be observed, that Darwin makes but slight account of these marked and sudden variations from the parent stock, but bases his theory of the origin of species mainly on the observed facts of small variations gradually accumulated by selective breeding. Other advocates of the theory attach a higher degree of importance to these sudden variations.

Keeping in mind these general facts of variation and laws of transmission, we turn to consider what advantage man has taken of them for the modification or improvement of the domestic breeds of plants and animals. Darwin designates by the name of selective breeding the agency of man in this line of effort. This process has risen to the rank of a high art, and in some of its aspects it might be dignified by the name of science. It began with the selection, by the rude cultivator or herdsman, of his breeding stock for its more obvious external qualities, such as color, size, general form, vigor and activity. As men became more observant, they studied their breeding stock more closely, and thus were enabled to match individuals more intelligently and skillfully. It is said that scientific breeders often give weeks or months of study to the individuals from which they propose to propagate. In this way, by the perpetuation and gradual accumulation of those small differences which are daily observed between parents and their offspring, varieties are produced, which deviate widely from the original stock. This is accomplished without any extraordinary variation from one generation to the next. But when the breeder is surprised by some startling innovation, like that of the progenitor of the otter breed of sheep, he eagerly seizes upon it as the means of making a long leap in the progress of experiment, which he is interested to pursue.

Though these facts and principles are alike applicable to plants and animals, the most obvious and familiar illustrations of them are drawn from the animal kingdom. Thus Darwin selects the various breeds of domesticated pigeons, as the exam

ple, par excellence, of what selective breeding can do, when aided by the tendency to variation, supplemented by the law of inheritance. He claims that the wild rock-pigeon is the well-known ancestor of all the domestic varieties; and yet that these descendants of a common ancestry have been brought, by selective breeding, to differ more from the parent stock and from each other, than do many well-recognized distinct species. These differences are said to extend, not only to superficial qualities, but to anatomical structure, and even to habits and instincts. The breeds of dogs and other domestic animals may be cited in illustration of the same principles.

With these illustrative facts and laws, we are prepared to pass from the barn-yard and farm to the theater of our entire globe, where the tendencies and laws of life have wrought on the scale of ages.

As we turn to wild nature, we find, in her living forms, the same tendencies to variation and the same laws of inheritance, with which we have become familiar in the domestic sphere. But we lack the agency of man to take advantage of those tendencies and laws by selective breeding. And here comes in Darwin's great principle of natural selection, to occupy on a wider scale the place held by selective breeding within narrower limits. That is, to use a personification, nature selects and breeds from those individuals, presented by variation, which are best adapted to the conditions of existence under which she nurtures and rears the various forms of life on earth. But the mode of her selection is widely different from that practiced by man. Nature is supposed to put the creatures of her care on a universal struggle for existence, in which she selects as her favorites only those which prove victorious in the conflict, leaving the less fortunate contestants to perish in the struggle. But this theory of natural selection requires a more extended elucidation, in order to its complete understanding.

In addition to the well-known tendency to vary, which seems to be a constitutional characteristic of all living beings, Darwin recognizes the influence of climate, soil, quality and supply of food, etc., as causes of variation,― the changes pro

duced by these causes being supposed to be perpetuated by hereditary descent. Whenever any one of the multiplied variations, which are sure to occur, fits the subject of it to suc ceed in the struggle for life, the fortunate individual survives the conflict and propagates his kind,— transmitting to his offspring the happy peculiarity which saved him from perishing, and which is to his descendants the guaranty of success in the contest to which they are born. The less favored varieties perish in the conflict, and leave their remains on the geological record of extinct species, while the survivors, according to Darwin's theory, go on by progressive changes to constitute new and distinct species.

The struggle for existence with plants is supposed to arise partly from external physical conditions of soil, climate, etc., partly from competition with other vegetable forms for roothold, breathing-space and sunlight, and partly from the destructive agency of animals that feed upon them. Any change which gives one variety an advantage in any of these respects, will ensure its preservation and the propagation of its advantages to its posterity. In like manner with animals the struggle for existence arises, partly from the external physical conditions of climate, as affecting their vital constitution, and of soil and climate, as related to an adequate supply of food, partly from competition with other animals, which consume the same kind of food, and partly from the destructive agency of other animals, which feed upon them. A few illustrations will set the subject in a clear light. They will be taken from the animal kingdom, as more obvious and impressive.

Take, for illustration, the animals inhabiting a cold climate. It is plain that any variation,-as increased length or thickness of fur,- which would enable the favored varieties to bear intense cold better than others, would save them from casualties by which great numbers of the less fortunate varieties would perish. One excessively severe winter might clear a whole region of the more thinly-clad varieties, leaving the more favored races in undivided possession.

Turn now to a hot climate, and take, as an example, what

has been regarded as a plausible account of the origin of the black races of men. It is well known that the heat and malaria of many parts of Africa prove fatal to white men, while the blacks thrive in health and vigor in the same regions. Suppose now, that the continent of Africa was first settled by whites. The effect of the climate would soon be seen in a general darkening of the complexion of the inhabitants. Occasional spontaneous variations would bring out individuals of unusual darkness of hue. As the population should increase and spread into the more sickly regions, the individuals of pale complexion would sink under the deadly influence of the climate, while the dusky varieties would live on, multiply and fill the continent. Thus, through natural selection, or the survival of the fittest, we should have a black population of millions, descended from an originally white race.

It is unnecessary to go into all the particulars of natural selection, as set forth by Darwin. It comes into operation wherever a spot of earth becomes crowded with its living inhabitants, where individuals and species must compete with each other for the means of subsistence. In such a contest, only the strongest and best would survive; and their advantages would, according to Darwin, be likely to depend on differences of structure and constitution, which had been gradually accumulated by natural selection.

Take, as another example of natural selection, the case of one race of animals, which is preyed upon by another, where swiftness of foot constitutes the only means of escape to the persecuted race. In such a case those varieties which are the best formed for speed will survive in larger proportion than others, while the slow-footed would largely fall a prey to their enemies. Thus a pack of wolves, operating on the race of deer, might prove as successful breeders and trainers for speed as the most eminent jockeys and lords of the turf.

Another mode of natural selection is appropriately named by Darwin sexual selection. This mode of selection operates mainly through the competition of males for the favor of the females,― the decision of the contest depending either on vic