Origin of Species Variorum

Comparison with 1866

for why should this one apparatus, given for the same special purpose to a few species which are so closely similar or rather identical in all other important points, have been made to differ?

Fritz Müller then argued to himself that this close similarity in so many points of structure must, in accordance with the views advanced by me, be accounted for by inheritance from a common progenitor. But as the vast majority of the species in the above two families, as well as the main body of crustaceans of all orders, are aquatic in their habits, it is improbable in the highest degree, that their common progenitor should have been adapted for breathing air. Müller was thus led carefully to examine and describe the apparatus in the few air-breathing species; and in each he found it to differ in several important points, as in the position of the orifices, in the manner in which they are opened and closed, and in some accessory details. ↑ Now, on the belief that species belonging to distinct families, already differing in some characters, and which whenever they varied would probably have varied in different manners, have been slowly adapted through natural selection to live more and more out of water and to breathe the air, it is quite intelligible, and might even have been con- fidently expected, that the structural contrivances thus acquired would in each case have materially differed, although serving for the same purpose. On the hypothesis of separate acts of creation the whole case must remain unintelligible, and we can only say, so it is. This line of argument seems to have had great weight in leading this distinguished naturalist fully to accept the views maintained by me in this volume. ↑

In the several cases just discussed, we have seen that in beings more or less remotely allied, the same end is gained and the same function performed by organs in appearance, though not in truth, closely similar. But the common rule throughout nature is that the same end is gained, even sometimes in the case of beings closely related to each other, by the most diversified means. How differently

for why should this one apparatus, given for the same .. purpose, have been made to differ, whilst all the other important organs were closely similar or rather identical. .. .. ...

Fritz Müller .. argues .. that this close similarity in so many points of structure must, in accordance with the views advanced by me, be accounted for by inheritance from a common progenitor. But as the vast majority of the species in the above two families, as well as most other crustaceans, are aquatic in their habits, it is improbable in the highest degree, that their common progenitor should have been adapted for breathing air. Müller was thus led carefully to examine .. the apparatus in the .. air-breathing species; and he found it to differ in each in several important points, as in the position of the orifices, in the manner in which they are opened and closed, and in some accessory details. Now such differences are intelligible, and might even have been expected, on the supposition that species belonging to distinct families had slowly become adapted to live more and more out of water, and to breathe the air. For these species, from belonging to distinct families, would have differed to a certain extent, and in accordance with the principle that the nature of each variation depends on two factors, viz. the nature of the organism and that of the surrounding conditions, their variability assuredly would not have been exactly the same. Consequently natural selection would have had different materials or variations to work on, in order to arrive at the same functional result; and the structures thus acquired would almost necessarily have differed. ↑ On the hypothesis of separate acts of creation the whole case .. remains unintelligible. .. .. .. .. .. .. .. .. This line of argument seems to have had great weight in leading Fritz Müller to accept the views maintained by me in this volume.

Another distinguished zoologist, the late Professor Claparède, has argued in the same manner, and has arrived at the same result. He shows that there are parasitic mites (Acaridæ), belonging to distinct sub-families and families, which are furnished with hair-claspers. These organs must have been independently developed, as they could not have been inherited from a common progenitor; and in the several groups they are formed by the modification of the fore-legs,— of the hind-legs,— of the maxillæ or lips,— and of appendages on the under side of the hind part of the body.

In the foregoing cases, we see the same end gained and the same function performed, in beings not at all or only remotely allied, ... by organs in appearance, though not in development, closely similar. On the other hand, it is a common rule throughout nature .. that the same end should be gained, even sometimes in the case of .. closely-related beings, by the most diversified means. How differently