VI. Divergence during evolution will be an advantage. “The same spot will support more life if occupied by very diverse forms.” Hence during the increase of species into its offspring--varieties, or sub-species, or true species, the latter “will try (only few will succeed) to seize on as many and as diverse places in the economy of nature as possible,” and so will tend to “exterminate its less well-fitted parent.” This explains classification, in which the organic beings “always _seem_ to branch and sub-branch like a tree from a common trunk; the flourishing twigs destroying the less vigorous--the dead and lost branches rudely representing extinct genera and families.” In a postscript he says:-- “This little abstract touches only the accumulative power of natural selection, which I look at as by far the most important element in the production of new forms. The laws governing the incipient or primordial variation (unimportant except as the groundwork for selection to act on, in which respect it is all important), I shall discuss under several heads, but I can come, as you may well believe, only to very partial and imperfect conclusions.” It is, I think, of especial interest to find Darwin at this early period arguing in a most convincing manner for the creative power of natural selection. The selective power becomes, by accumulation, of such paramount importance in the process, as compared with the variations, that, although these latter are absolutely essential, man may be said to _make_ his domestic breeds and Nature her species. The man who argued thus had been through and had left behind the difficulty that, even now, is often raised--that “before anything can be selected it must be,” and therefore that selection is of small account as compared with variation. CHAPTER X. WALLACE’S SECTION OF THE JOINT MEMOIR READ BEFORE THE LINNEAN SOCIETY JULY 1, 1858. The communication by Alfred Russel Wallace was entitled “On the Tendency of Varieties to depart indefinitely from the Original Type.” An abstract of it is given below. [Sidenote: WALLACE’S ESSAY.] _Varieties_ produced in domesticity are more or less unstable, and often tend to return to the parent form. This is usually thought to be true for all varieties, and to be a strong argument for the original and permanent distinctness of species. On the other hand, races forming “permanent or true varieties” are well known, and there are generally no means of determining which is the _variety_ and which the original _species_. The hypothesis of a “permanent invariability of species” is satisfied by supposing that, while such varieties cannot diverge from the species beyond a certain fixed limit, they may return to it.