put it most forcibly and clearly. I am much pleased to see how carefully you have read my book, and, what is far more important, reflected on so many points with an independent spirit. As I am deeply interested in the subject (and I hope not exclusively under a personal point of view), I could not resist venturing to thank you for the right good service which you have done.-Pray believe me, dear sir,

Yours faithfully and obliged,

CHARLES DARWIN.

In

This letter is interesting for three reasons. the first place, it shows well the caution of Darwin, who never pretended to have proved anything beyond what the evidence warranted. the second place, it shows his kindness and courtesy to young naturalists, who, like myself, were quite unknown to him. It is astonishing that he, in his mature judgment, should speak in terms of encouragement about a juvenile essay, which I should now regret having published, if it had not been the means of procuring me the letter I have just read to you. And, in the third place it shows how strong, at the time, the current of popular opinion must have been against him, when he so much appreciated the sympathy of an unknown naturalist. How rapid has been the change! Let us try to find the reason for this by comparing the argument which failed with Lamarck with that which succeeded in the hand of Darwin.

DARWIN'S ARGUMENT COMPARED WITH THAT

OF LAMARCK

Lamarck commenced by an induction from the facts of classification, and came to the conclusion that species do not differ essentially from varieties. So far he was right; but he then goes on to assume, without any reasons, that varieties are due to climate; which is not a legitimate induction from anything we know, as I shall show later on. He then argues that, as changes in physical geography take place slowly, therefore climate, and with it the habits of the plants and animals, must also slowly change, and, consequently, they will pass through the stage of varieties into that of new species. The only rational explanation he gives for these changes is the use or disuse of organs; an explanation quite inadequate. The argument as to the cause of change was a failure. He gave no explanation of the extinction of intermediate forms; and his induction, that species were of a similar nature to varieties, was founded on far too limited a range of facts to carry, by itself, conviction of its truth.

Darwin sets to work very differently. He prepares the way by giving an account of the facts of variation in plants and animals under domestic

ation, and shows how these variations have been gradually accumulated, generation after generation, by the artificial selection of man, partly in a methodical way and partly unmethodical, until the most dissimilar varieties have been produced from the same stock. These varieties of the same species, he points out, differ from each other in much the same manner as do the species of a genus in a state of nature. He then proceeds to give the facts of variation in a natural state, and comes to the same conclusion that Lamarck had arrived at before him, that species resemble varieties in many respects. But he does not stop here; he proceeds to put this conclusion to the proof, by making a deduction which can be verified. He says, "If it be true that species resemble varieties, then the species of the larger genera ought to be more variable (that is, ought to contain more varieties) than the species belonging to smaller genera." To test this, he arranged the plants of twelve countries, and the beetles of two districts, in two nearly equal masses, the species of the larger genera on one side and those of the smaller genera on the other; and in every case it turned out that a larger proportion of the species on the side of the larger genera presented more varieties than

those on the side of the smaller genera; thus verifying his deduction.

Having thus laid a firm foundation, he next offers an explanation of how varieties change into species. He shows that plants and animals tend to increase very rapidly, while the amount of vegetation (and consequently the amount of animal life also) which the earth can support is strictly limited; and so proves that more organisms come into existence than can possibly live; that, in fact, in each year as many must die as are born; and this gives rise to a struggle for exist

ence.

Putting together, now, the fact of variation and the fact of the struggle for existence, he shows that generally those varieties which are best adapted to succeed in life will live the longest, and will leave most offspring, while the others will be killed off. The successful individuals will hand down their useful characters to their offspring, occasionally in a still more useful form; and thus useful variations will tend more and more to improve, and succeeding generations will diverge more and more from the original stock. This process he calls natural selection; and he shows how by its means the classification of all organic beings can be explained, and how it

would necessarily tend towards a general advance of organisation, although lowly forms would still survive to occupy their appropriate places in the scheme of nature, while some might even retrograde.

He then examines the laws of variation, of which he acknowledges our ignorance to be profound-discusses how much may be due to change in external conditions, and shows how use of one organ and disuse of another may bring about rudimentary structures by the unused parts becoming atrophied from want of sufficient nourishment.

This concludes the first part of his argument; and, before advancing, he proceeds to discuss the objections—including that of hybridism—that may be urged against the theory, and says that some of them are so serious that he cannot reflect on them without in some degree being staggered; but that, to the best of his judgment, the greater number are only apparent, while those that are real are not, he thinks, fatal to the theory. In this part of the book very nearly every objection that has since been made was considered in a thoroughly impartial manner, everything that could be urged against the theory being stated most forcibly; and its transparent honesty did as