5}
he writes of the 1844 Essay, "But at that time I overlooked one problem
of great importance.... This problem is the tendency in organic beings
descended from the same stock to diverge in character as they become
modified." The absence of the principle of divergence is of course also
a characteristic of the sketch of 1842. But at p. 37, the author is not
far from this point of view. The passage referred to is: "If any
species, _A_, in changing gets an advantage and that advantage ... is
inherited, _A_ will be the progenitor of several genera or even families
in the hard struggle of nature. _A_ will go on beating out other forms,
it might come that _A_ would people <the> earth,--we may now not have one
descendant on our globe of the one or several original creations{26}."
But if the descendants of _A_ have peopled the earth by beating out
other forms, they must have diverged in occupying the innumerable
diverse modes of life from which they expelled their predecessors. What
I wrote{27} on this subject in 1887 is I think true: "Descent with
modification implies divergence, and we become so habituated to a belief
in descent, and therefore in divergence, that we do not notice the
absence of proof that divergence is in itself an advantage."

{25} _Life and Letters_, i. p. 84.

{26} In the footnotes to the Essay of 1844 attention is called to
similar passages.

{27} _Life and Letters_, ii. p. 15.

The fact that there is no set discussion on the principle of divergence
in the 1844 Essay, makes it clear why the joint paper read before the
Linnean Society on July 1, 1858, included a letter{28} to Asa Gray, as
well as an extract{29} from the Essay of 1844. It is clearly because the
letter to Gray includes a discussion on divergence, and was thus,
probably, the only document, including this subject, which could be
appropriately made use of. It shows once more how great was the
importance attached by its author to the principle of divergence.

{28} The passage is given in the _Life and Letters_, ii. p. 124.

{29} The extract consists of the section on _Natural Means of
Selection_, p. 87.

I have spoken of the hurried and condensed manner in which the sketch of
1842 is written; the style of the later Essay (1844) is more finished.
It has, however, the air of an uncorrected MS. rather than of a book
which has gone through the ordeal of proof sheets. It has not all the
force and conciseness