diverse hardships which at times beset all living things, and which are intensified by the Malthusian law of the pressure of population on subsistence, — population tending to multiply in geometrical progression, while food can increase only in a much lower ratio, and, room may not be increasable at all, so that out of multitudinous progeny only the few fittest to the. special circumstances in each generation can possibly survive and propagate,- this is Darwinism; that is, Darwinism pure and simple, free from all speculative accretions.

Here, it may be remarked that natural selection by itself is not an hypothesis, nor even a theory. It is a truth, a catena of facts and direct inferences from facts. As has been happily said, it is a truth of the same kind as that which we enunciate in saying that round stones will roll down a hill further than flat ones. There is no doubt that natural selection operates; the open question is, what do its opera tions amount to. The hypothesis based on this principle is, that the struggle for life and survival of only the fittest among individuals, all disposed to vary and no two exactly alike, will account for the diversification of the species and forms of vegetable and ani

mal life, will even account for the rise, in the course of countless ages, from simpler and lower to higher and more specialized living beings.

We need not here enter into any further explanation of this now familiar but not always well-understood hypothesis; nor need I here pronounce any judgment of my own upon it. No doubt it may account for much which has not received other scientific explanation; and Mr. Darwin is not the man to claim that it will account for every thing. But before we can judge at all of its capabilities, we need clearly to understand what is contained in the hypothesis; for what can be got out of it, in the way of explanation, depends upon what has gone into it. So certain discriminations should here be attended to.

Natural selection we understand to be a sort of personification or generalized expression for the processes and the results of the whole interplay of living things on the earth with their inorganic surroundings and with each other. The hypothesis asserts that these may account, not for the introduction of life, but for its diversification into the forms and kinds which we now behold. This, I suppose, is tantamount to asserting that the differences between one

species and another now existing, and between these and their predecessors, has come to pass in the course of Nature; that is, without miracle. In these days, all agree that à scientific inquiry whether this may be so- that is, whether there are probable grounds for believing it (no thoughtful person expects to prove it)-is perfectly legitimate; and, so far as it becomes probable, I imagine that you might safely accept it. For the hypothesis, in its normal and simplest form,when kept close to the facts, and free from extraneous assumptions-is merely this:

Given the observed capacity for variation as an inexhaustible factor, assuming that what has varied is still prone to vary (and there are grounds for the assumption), and natural selection will so to say-pick out for preservation the fittest forms for particular surroundings, lead on and diversify them, and, by continual elimination of the less fit, segregate the survivors into distinct species. This, you see, assumes, and does not account for, the impulse to variation, assumes that variation is an inherent and universal capacity, and is the efficient cause of all the diversity; while natural selection is the proximate cause of it. So it is the selection, not the creation of forms that is accounted for.

Darwinism does not so much explain why we have the actual forms, as it does why we have only these and not all intermediate forms, -in short, why we have species. There is of course a cause for the variation. Nobody supposes that any thing changes without a cause; and there is no reason for thinking that proximate causes of variation may not come to be known; but we hardly know the conditions, still less the causes now. The point I wish to make here is that natural selection - however you expand its meaning-cannot be invoked as the cause of that upon which it operates, i. e., variation. Otherwise, if by natural selection is meant the totality of all the known and unknown causes of whatever comes to pass in organic nature, then the term is no longer an allowable personification, but a sheer abstraction, which meaning every thing, can explain nothing. It is like saying that whatever happens is the cause of whatever comes to pass.

We may conclude, therefore, that natural selection, in the sense of the originator of the term, and in the only congruous sense, stands for the influence of inorganic nature upon living things, along with the influence of these upon each other; and that what it purports to ac

count for is the picking out, from the multitude of incipient variations, of the few which are to survive, and which thereby acquire distinctness.

There is a further assumption in the hypothesis which must not be overlooked; namely, that the variation of plants and animals, out of which so much comes, is indefinite or all-directioned and accidental. This, I would insist, is no fundamental part of the hypothesis of the derivation of species, and is clearly no part of the principle of natural selection. But it is an assumption which Mr. Darwin judges to be warranted by the facts, and in some of its elements it is unavoidable. Evidently if the innate tendency to vary upon which physical circumstances operate is indefinite, then the variations which the circumstances elicit, and which could not otherwise amount to any thing, must be accidental in the same sense as are the circumstances themselves. Out of this would immediately rise the question as to what can be the foundation and beginning of this long and wonderful chapter of accidents which has produced and maintained, not only for this time but through all biological periods, an ever-varying yet ever well-adapted cosmos.

But the facts, so far as I can judge, do not

support the assumption of every-sided and indifferent variation. Variation is somehow and somewhere introduced in the transit from parent to offspring. The actual variations displayed by the progeny of a particular plant or animal may differ much in grade, and tend in more than one direction, but in fact they do not appear to tend in many directions. It is generally agreed that the variation is from within, is an internal response to external impressions. All that we can possibly know of the nature of the inherent tendency to vary must be gathered from the facts of the response. And these, I judge, are not such as to require or support the assumption of a tendency to wholly vague and all-directioned variation.

Let us here correct a common impression that Darwinian evolution predicates actual or necessary variation of all existing species, and counts that the variation must be in some definite ratio to the time. That is not the idea, nor the fact. "Evolution is not a course of hap-hazard and incessant change, but a continuing re-adjustment, which may or may not, according to circumstances, involve considerable changes in a given time." Every form is in a relatively stable equilibrium, else it would not