The ambiguity of this sentence evidently misled Wallace into believing that the single variations were considered of paramount importance. Darwin therefore wrote again (February 2nd):—
“I must have expressed myself atrociously; I meant to say exactly the reverse of what you have understood. F. Jenkin argued in the ‘North British Review’ (June 1867) against single variations ever being perpetuated, and has convinced me, though not in quite so broad a manner as here put. I always thought individual differences more important; but I was blind and thought single variations might be preserved much oftener than I now see is possible or probable. I mentioned this in my former note merely because I believed that you had come to a similar conclusion, and I like much to be in accord with you. I believe I was mainly deceived by single variations offering such simple illustrations, as when man selects.”
From these two letters to Wallace we see that the latter was the first to give up the larger variations in favour of ordinary individual differences.
Darwin also wrote to Victor Carus on May 4th, 1869:—
“I have been led to ... infer that single variations are even of less importance, in comparison with individual differences, than I formerly thought.”
There has been much misconception on this point, and a theory of evolution by the selection of large single variations—a view held by many, but not by Darwin—has been passed off as the Darwinian theory of natural selection. It is surprising that this old mistake should have been repeated at so recent a date, and on so important an occasion as the Presidential Address to the British Association at Oxford on August 8th, 1894, and that so ill-aimed a criticism should have been quoted with approval in a leading article in the Times of the following day. The following extracts from Lord Salisbury’s address unfortunately leave no doubt on the matter:
LORD SALISBURY’S CRITICISM.
“What is to secure that the two individuals of opposite sexes in the primeval forest, who have been both accidentally blessed with the same advantageous variation shall meet, and transmit by inheritance that variation to their successors?... The biologists do well to ask for an immeasurable expanse of time, if the occasional meetings of advantageously varied couples from age to age are to provide the pedigree of modifications which unite us to our ancestor the jelly-fish.... There would be nothing but mere chance to secure that the advantageously varied bridegroom at one end of the wood should meet the bride, who by a happy contingency had been advantageously varied in the same direction at the same time at the other end of the wood. It would be a mere chance if they ever knew of each other’s existence—a still more unlikely chance that they should resist on both sides all temptations to a less advantageous alliance. But unless they did so, the new breed would never even begin, let alone the question of its perpetuation after it had begun.”
It is of interest to reproduce Lord Salisbury’s words in close proximity to Darwin’s real statements on the subject, as shown in the letters to his friends—statements which are also expressed in many places in his published works.
The joint paper was read before the Linnean Society on July 1st, 1858, about a fortnight after Wallace’s essay had been received by Darwin. There was no discussion, but the interest and excitement at the meeting were very great, owing in large part to the influential support with which the new theory came before the scientific world. Darwin appreciated the importance of this support at its true value, for he wrote to Hooker, July 5th:—