The Editor of the Daily Chronicle.

     Sir,--In your notice, on Thursday last, of Captain Hutton's book having the above title your reviewer quotes a passage on the peculiar coloration of the species of small fruit-pigeons of Malaisia and Polynesia, which is supposed by the author to prove that their diversities of color cannot be "recognition-marks." As I am the author of the theory of recognition-marks, and have applied it to explain the markings in this very group, perhaps you will allow me to show, in as few words as possible, that Captain Hutton's argument does not apply, when all the circumstances are taken into consideration; and this is the more necessary as your reviewer refers to the passage as a "destructive criticism" of the theory in question.

     The last seven lines of the quotation are those which involve the fallacious argument, and are as follows:--

     Consequently it appears certain that most of these species were developed singly, each on its own island. If this be the case, the colors which now distinguish the different species cannot be recognition-marks, because there is no other species in each island with which they could be confounded.

     The fallacy of this argument lies in not considering the full meaning of the word "developed." For if he had asked himself, "Developed from what?" he would have seen that each must have been developed from some other species which had accidentally reached the island. During the process of modification which was required to bring the old species into harmony with the new conditions of its new home there would necessarily be a time when there were two forms living side by side--the immigrant species and the partially modified form or incipient new species which was to replace it; and in order that the process of modification and adaptation to new conditions should be carried on and completed it is universally admitted that the intercrossing of the two forms must in some way be checked. Now, some distinctive marking enabling each kind to know its fellows is one of the best ways of effecting this, and therefore all suitable variations of color and marking, which were not otherwise injurious, would be preserved and gradually intensified in the very process of development of the new species. When this was completed, after perhaps hundreds or thousands of years, the original species, being less adapted to the conditions of existence, would be crowded out, and the modified form alone remain, preserving those peculiarities of color or marking which now seem useless, but which were really one of the essentials to its development.

     Such of your readers as have studied the theory of development by natural selection will, I am sure, understand this explanation; while those to whom the subject is new will find the theory of recognition-marks explained, with illustrations, in my book on Darwinism, p. 217, while on p. 227 is a too brief reference to its use in the process of differentiation by checking intercrossing.

--I am, Sir, yours, &c.,
Alfred R. Wallace.