“With respect to the distinct species of the same genus which, _on my theory_, must have spread from one parent source, if we make the same allowances as before,” &c.
“On my theory” became “on our theory” in 1869.
“_On my theory_ these several relations throughout time and space are intelligible; . . . the forms within each class have been connected by the same bond of ordinary generation; . . . in both cases the laws of variation have been the same, and modifications have been accumulated by the same power of natural selection” (p. 410).
“On my theory” became “according to our theory” in 1869, and natural selection is no longer a power, but has become a means.
“_I believe that something more is included_, and that propinquity of descent—the only known cause of the similarity of organic beings—is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classification” (p. 418).
“_Thus_, _on the view which I hold_, the natural system is genealogical in its arrangement, like a pedigree” (p. 422).
“On the view which I hold” was cut out in 1872.
“We may feel almost sure, _on the theory of descent_, that these characters have been inherited from a common ancestor” (p. 426).
“_On my view of characters being of real importance for classification only in so far as they reveal descent_, we can clearly understand,” &c. (p. 427).
“On my view” became “on the view” in 1872.
“The more aberrant any form is, the greater must be the number of connecting forms which, _on my theory_, have been exterminated and utterly lost” (p. 429).
The words “on my theory” were excised in 1869.
“Finally, we have seen that _natural selection_ _. . . explains_ that great and universal feature in the affinities of all organic beings, namely, their subordination in group under group. _We use the element of descent_ in classing the individuals of both sexes, &c.; . . . _we use descent_ in classing acknowledged varieties; . . . and I believe this element of descent is the hidden bond of connection which naturalists have sought under the term of the natural system” (p. 433).
Lamarck was of much the same opinion, as I showed in “Evolution Old and New.” He wrote:—“An arrangement should be considered systematic, or arbitrary, when it does not conform to the genealogical order taken by nature in the development of the things arranged, and when, by consequence, it is not founded on well-considered analogies. There is a natural order in every department of nature; it is the order in which its several component items have been successively developed.” { 195a} The point, however, which should more particularly engage our attention is that Mr. Darwin in the passage last quoted uses “natural selection” and “descent” as though they were convertible terms.