TRANSACTIONS OF SECTION D. 809 
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 advan- 
tageously 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.’ 
Professor Huxley, in seconding the vote of thanks to the President, said that 
he could imagine that certain parts of the address might raise a very good dis- 
cussion in one of the Sections, and I have little doubt that he referred to these 
criticisms and to this Section. When I had to face the duty of preparing this 
address, I could find no subjects better than those provided by Lord Salisbury. 
At first the second objection seemed to offer the more attractive subject. It 
was clear that the theory of natural selection as held by Darwin was misconceived 
by the speaker, and that the criticism was ill-aimed. Darwin and Wallace, from the 
very first, considered that the minute differences which separate individuals were 
of far more importance than the large single variations which occasionally arise— 
Lord Salisbury’s advantageously varied bride and bridegroom at opposite ends of the 
wood. In fact, after Fleeming Jenkins’s criticisms in the ‘ North British Review’ 
for June 1867, Darwin abandoned these large single variations altogether. Thus 
he wrote in a letter to Wallace (February 2, 1869): ‘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.’ Hence we may infer that 
the other great discoverer of natural selection had come to the same conclusion at 
an even earlier date. But this fact removes the whole point from the criticism 
I haye just quoted. According to the Darwin-Wallace theory of natural selection, 
individuals sufficiently advantageously varied to become the material for a fresh 
advance when an advance became necessary, and at other times sufficient to main- 
tain the ground previously gained—such individuals existed not only at the 
opposite ends of the wood, but were common enough in every colony within its 
confines. The mere fact that an individual had been able to reach the con- 
dition of a possible bride or bridegroom would count for much. Few will dispute: 
that such individuals ‘have already successfully run the gauntlet of by far the 
greatest dangers which beset the higher animals (and, it may be added, the lower 
animals also |—the dangers of youth. Natural selection has already pronounced a 
satisfactory verdict upon the vast majority of animals which have reached 
maturity.’ ? 
But the criticism retains much force when applied to another theory of evolution 
_ by the selection of large and conspicuous variations, a theory which certain writers 
have all along sought to add to or substitute for that of Darwin. Thus Huxley 
from the very first considered that Darwin had burdened himself unnecessarily in 
rejecting per saltum evolution so unreservedly.’ And recently this view has been 
revived by Bateson’s work on variation and by the writings of Francis Galton. I 
had at first intended to attempt a discussion of this view, together with Lord 
Salisbury’s and other objections which may be urged against it; but the more the 
two were considered, the more pressing became the claims of the criticism alluded 
to at first—the argument that the history of our planet does not allow sufficient 
time for a process which all its advocates admit to be extremely slow in its 
operation. I select this subject because of its transcendent importance in relation 
to organic evolution, and because I hope to show that the naturalist has something 
of weight to contribute to the controversy which has been waged intermittently 
ever since Lord Kelvin’s paper ‘On Geological Time’ * appeared in 1868. It has 
_ been urged by the great worker and teacher who occupied the Presidential Chair 
1 Life and Letters, vol. iii. 2 Poulton, Colours of Animals, p. 308. 
3 See his letter to Darwin, November 23, 1859: Life and Letters, vol. ii. 
‘ Trans. Geol. Soc., Glasgow, vol. iii. See also‘ On the Age of the Sun’s Heat,’ 
Macmillan, March 1862: reprinted as Appendix to Thomson and Tait, Natural Philo- 
1896. 3G 
