Charles Darwin and the Theory of Natural Selection

by Sir Edward Bagnall Poulton

Darwin, too, wrote a very large number of memoirs for the scientific societies, as may be seen from the list in Appendix III. of the “Life and Letters,” but the volumes which he subsequently published included all the previous details, with the addition of much new matter, and it is these volumes rather than the original communications which form the authoritative statement of his investigations. Such a method was possible and desirable with the subjects upon which he worked, all of which were of great interest to the thinking part of the general public, as well as to the experts; but in less attractive subjects it is not probable that the plan could be carried out in this country with any prospect of success.

It has already been stated that Darwin looked on the “Origin of Species” as a short abstract of a greater work he intended to publish. It is likely that he at first contemplated a comprehensive work like the “Origin” itself, but soon found that his notes on domesticated animals and plants, the general results of which had been condensed into the first three chapters of the “Origin,” would form a work more than twice the size of the latter. He began arranging these notes on January 9th, 1860 (January 1st is the date given in the “Autobiography”), as soon as the second edition of the “Origin” was off his hands, but his “enormous correspondence,” as he calls it in the “Autobiography,” with friends about the “Origin,” and the reviews and discussions upon it, must have occupied a large part of his time; and then there was the third edition to bring out (published April, 1861). This edition must have cost much labour, as many parts were modified and enlarged to meet the objections or misunderstanding of reviewers.

Francis Darwin tells us that the third chapter of “Animals and Plants, &c.,” was still on hand at the beginning of 1861. His work on this book was furthermore interrupted by illnesses and by other researches. Thus, during 1860 he worked at Drosera, and during the latter part of 1861 and beginning of 1862 at the fertilisation of orchids. In his diary for 1866 we meet with the entry, “Nov. 21st—Finished ‘Pangenesis,’” and later on, “Dec. 22nd—Began concluding chapter of book.” In this year, too, he brought out the fourth edition of the “Origin.” When the time for publication approached Darwin was much disappointed at the dimensions of the work. It was not published till January 30th, 1868, when it was proved that his fears were groundless, for a second edition of 1,250 copies were required in the following month, the 1,500 of the first edition having been all absorbed.

This work is considered by some writers to be the greatest produced by Darwin; but I think we shall be right in accepting his own opinion that such words should be applied to the “Origin.” It is probable, however, that this book stands second in importance in the splendid list of works which have done so much to increase our knowledge of nature and to inspire others to continue the good work.

ON VARIATION.

“The Variation of Animals and Plants under Domestication” opens with a very clearly written account of natural selection; it proceeds to treat of the domestic quadrupeds and birds, describing the differences between the various breeds of each species, and making out as far as possible the history of their development from each other and from the wild stock. Cultivated plants are then treated in the same manner. The first volume concludes with two most important chapters on bud-variation and anomalous modes of reproduction, and on inheritance.

The second volume deals with inheritance, crossing, effect of conditions of life, sterility, hybridism, selection by man, causes and laws of variability. Finally, all the main lines are brought to a common centre in the wonderful chapter in which he discloses his “provisional hypothesis of pangenesis.” This is of such interest, and is so characteristic of its author’s power of viewing the most divergent facts from a common standpoint, that it is desirable to give a tolerably full account of it.

The following is a brief statement of the various classes of facts which Darwin attempted to connect by his hypothesis.

Reproduction is sexual and asexual, and the latter is of various kinds, although their differences are more apparent than real. It may be concluded that gemmation or budding, fission or division, the repair of injuries, the maintenance of each part, and the growth of the embryo “are all essentially the results of one and the same great power.”

In parthenogenesis the ovum can develop without fertilisation, and hence the union of germs from different individuals cannot serve as an essential characteristic of sexual, as compared with asexual, generation. Although sexually-produced individuals tend to vary far more than those which are produced asexually, this is not always the case, and the variability, when it occurs, is subject to the same laws. Sexually-produced individuals very generally pass in development from a lower to a higher grade; but this can hardly be said to occur in certain forms, such as Aphis, etc.