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sects), over two hundred thousand known kinds, and probably at least as many more yet to be examined and described; if the population of the earth is as varied as this, one cannot help asking the question, “How has this multitude of kinds come into being, and what is the use of the earth supporting such a variety of animals and plants ?” I may as well begin this account of the development theory by saying, that the latter is the first scientific attempt that has ever been made to explain the origin of species. By species, naturalists mean much the same thing as is expressed by the commoner word kinds;" but species is the more exact term, and so, for scientific purposes, the better one to use. A few simple instances will make this clear.
The russet, the baldwin, the pippin, and the greening, are all well-known kinds of apples; yet they are not reckoned as species, but only as varieties of one species, — the apple. Then, again, there are the different kinds or breeds of hens, - the game-fowl, the black Spanish, the Cochin, the Dorking, and so on; all of them classed as varieties of one species, — the domestic fowl.
In these instances the word “kind” means something less than “species;” that is, it does not take in so many sorts of things as the species does. But sometimes the reverse is true: as, for example, when we speak of the different kinds of cone-bearing evergreen trees, such as pines, firs, red cedars, and so on; for the pines themselves comprise many species, the firs many more, and so with others of the evergreens. In the classification of animals and plants, such kinds, or divisions, as are made up of things very closely alike, and generally capable of producing others much like themselves, are called "species." The species, again, are assembled into larger groups, called genera. To make the matter plainer still,
, let me illustrate it by means of the maple genus. It has five species that are found in the northern United States, east of the Mississippi ; of which the best known are the sugar-maple, the red maple, and the water-maple.
The first of these has two varieties, – the common and the black; while the remaining species have no strongly marked varieties: so that the whole genus might be classified in tabular form thus:
Now, when we look at the living things of the world about us, we see that the rule seems to be, that life, on the whole, goes on with no great changes from year to year in the species of animals or plants. New individuals come into being, grow mature, become old, and die, only to leave others like themselves; and so the species is continued, while the separate animals or plants of which it is composed, one after another disappear. And not only is there usually
great change noticeable during the lifetime of one man; but the pictures, mummies, and other records which have come down to our time from the Egypt of several thousand years ago, prove that the animals and plants of to-day are, in that country at any rate, just about what they then were. It is, from the consideration of this and other similar facts, not unnatural, that, until very lately, men should quite generally have believed that the living forms with which we are fainiliar were created, that is, were suddenly placed upon the earth, in much the same condition in which we now see them.
The father of natural history, the great Swed
1 Although this is true of the Egypt of some thousands of years ago, it is by no means true of most countries at a period even so comparatively recent as that just preceding the dawn of written history.
ish naturalist, Linnæus, expressly stated, “There are as many different species as there were different forms created in the beginning by the Infinite Being.” And, after quoting this statement, Professor Haeckel, of the University of Jena, Germany (himself one of the greatest of living zoologists), goes on to state Linnæus's idea of the way in which the animals and plants, after the stranding of the ark, may have lived for a time on Mount Ararat, which in itself, by its situation and height, offers a range of temperature that might suit the needs of a great variety of beings. To this, Professor Haeckel objects, that it would have taken but a very short time for the beasts of prey to destroy all the other animals, or for the latter to eat all the plants. In fact, he argues we cannot believe that the balance of nature could be preserved, if only one or a pair of each species of living things had been created at the outset, or had been rescued in the way just described.
It would seem, indeed, as though there could be no need of even so much as referring to such crude ideas as those of Linnæus just quoted; but there are still many people in the world whose belief is so closely like his, that this sentence would fairly express their thought. But no one, perhaps, has ever more vividly pictured this process by which all living things are by many supposed to have come into being than has Milton in the well-known lines :
1 Natural History of Creation, pp. 43-45.
“Out of the ground uprose,
The grassy clods now calved; now half appear'd
In much the same way the poet goes on at length to describe the creation of other animals. It may be said that the conception just given is that of a poet, and not of a man of science; but for my present purpose this makes no differ
It is, first of all, to those who have no more scientific conception of the process by which living beings have come to exist on the earth than that of Milton, that the present work is addressed. Linnæus's and Milton's explanation of the origin of species are statements of
1 Paradise Lost, book vii. 1. 456 et seq.