a century ago. In this place there will only be room for allusion to a very few of the more important steps that have been taken in advancing the theory to its present comprehensiveness.

Herbert Spencer has laid down as a general principle, that the early beliefs of mankind are not usually true beliefs. This is but one special application of the truth, now generally recognized by students of the human race, that man has arisen from an extremely rude and unintelligent condition to the position which he now occupies. The ideas of a savage are no less inferior to our own than are his manners or his morals. And, even long after the savage condition has been left behind, men's conceptions of the laws of nature remain exceedingly imperfect.

Until the eighth century it was universally believed that all substances consisted of earth, air, fire, and water united in various proportions. The circulation of the blood seems to have been merely guessed at, until it was definitely announced by Harvey in 1619; and, up to that time, physiologists in general contentedly acquiesced in the opinion of the ancients, that the blood remains stagnant, or nearly so, throughout the veins. For a long time the arteries were thought to be filled with air.

Our

word "artery" comes from a Greek noun meaning either windpipe or artery.

Till about three hundred and fifty years ago, the sun, planets, and stars were thought, even by astronomers, to be set in hollow, crystal spheres, which revolve about the earth.

It is only within the present century that the various forces of nature have been recognized as interchangeable forms of energy, convertible one into the other. Heat, light, and electricity, instead of being (as at present) known as so many forms of energy, were long considered to be substances, the presence or absence of which in any object made it hot or cold, light-giving or dark, electrified or not. But this misinterpretation of nature did not always proceed from any lack of reasoning power in the scientists of the previous century and of earlier times. There have been few greater thinkers on natural and physical science than Aristotle,1 and yet any intelligent high-school pupil of our time may understand a multitude of laws of which the great Greek philosopher was ignorant, only because, in his day, the facts from which the laws have been inferred were still unknown. Coming late as it does, the statement of the

1 Died 381 B.C.

development theory in its present form has been able to take into account a vast array of carefully observed facts, the existence of which the naturalist of two generations ago could not have foreseen.

As late as the beginning of the present century there was not enough known of the facts of embryology, zoölogy, botany, paleontology, and geographical distribution, to enable any naturalist, of however penetrating a mind, to form an adequate conception of the processes by which species have come into being. And yet there were not lacking naturalists who saw far enough into the influence exerted upon animals and plants by their surroundings to attribute to this influence as a cause the existence of many, if not all, species. Says Darwin,

"It is rather a singular instance of the manner in which similar views arise at about the same time, that Goethe in Germany, Dr. Darwin in England, and Geoffroy Saint-Hilaire (as we shall immediately see) in France, came to the same conclusion on the origin of species in the years 1794-95.”1

Besides Goethe, three other great German thinkers, Kant, Treviranus, and Oken, set forth,

1 Origin of Species, Historical Sketch, p. xiv.

between 1790, and 1809, arguments in favor of organic evolution. Of all the authors just mentioned, however, only Saint-Hilaire was a professional naturalist, and even he failed to conceive of the development theory in any thing at all closely like its present form. Dr. Darwin, however, came nearer to a comprehension of the real meaning of organic evolution than any of his contemporaries, and he fully deserves the high praise that has been given him by Ernest Krause:

"It is only now, after the lapse of a hundred years, that, by the labors of one of his descendants, we are in a position to estimate at its true value the wonderful perceptivity, amounting almost to divination, that he displayed in the domain of biology. . . . The elder Darwin was a Lamarckian, or, more properly, Jean Lamarck was a Darwinian of the older school, for he has only carried out further the ideas of Erasmus Darwin, although with great acumen; and it is to Darwin, therefore, that the credit is due of having first established a complete system of the theory of evolution.”1

The justice of this estimate any one may easily verify by reading for himself the thirty-ninth section of Dr. Darwin's most valuable work, the "Zoonomia," published in 1794. In this sec

1 The Life of Erasmus Darwin, American edition, pp. 132, 133.

tion he gives a careful summary of his reasons for maintaining the doctrine of organic evolution; but I can only quote here the paragraph in which are summed up his conclusions in regard to the origin of the warm-blooded animals:

"From thus meditating on the great similarity of the structure of the warm-blooded animals, and at the same time of the great changes they undergo both before and after their nativity, and by considering in how minute a proportion of time many of the changes of animals above described have been produced, would it be too bold to imagine that in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind, - would it be too bold to imagine that all warm-blooded animals have arisen from one living filament,1 which the great First Cause endued with animality, with the power of acquiring new parts attended with new propensities, directed by irritations, sensations, volitions, and associations, and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down those improvements by generation to its posterity, world without end?” 2

It is impossible in a single selection, of whatever length, to give a just idea of the thorough

1 Dr. Darwin's use of the word "filament" arises from a misapprehension which he shared, with the naturalists of his time, in regard to the origin of the embryo in the process of generation. The ovum was known to exist, but its importance was not recognized.

2 Zoonomia, xxxix. 4, 8.