2 64 



NA TURE 



\Fcb. I, 1872 



verse criticism which the hypothesis has met with, espe- 

 cially in France, has, I think, arisen from the misappre- 

 hension thus caused. The expression, " Survival of the 

 Fittest," seemed to me to have the advantage of suggesting 

 no thought beyond the bare fact to be expressed ; and 

 this was in great part, though not wholly, the reason for 

 using it. 



Prof. Cope's indirect statement, that I have said 

 nothing to explain ''the origin" of the fittest, is equally 

 erroneous with his direct statement which I have just 

 corrected. In the " Principles of Biology," sec. 147, I 

 have contended that no " interpretation of biologic evolu- 

 tion which rests simply on the basis of biologic induction, 

 is an ultimate interpretation. The biologic induction 

 must be itself interpreted. Only when the process of 

 evolution of organisms is affiliated on the process of evolu- 

 tion in general, can it be truly said to be explained. 

 . . . We have to reconcile the facts with the universal 

 laws of re-distribuiion of matter and motion." After two 

 chapters treating of the " lixternal Factors " and "Internal 

 Factors," which are dealt with as so many acting and re- 

 ading forces, there come two chapters on " Direct Equi- 

 libration" and "Indirect Equilibration" — titles which 

 of themselves imply an endeavour to interpret the facts in 

 terms of Matter, Motion, and Force. It is in the second 

 of these chapters that the phrase "Survival of the Fittest" 

 is first used ; and it is there used as the most convenient 

 ph\ Biological equivalent for the purely physical statement 

 which precedes it. 



Respecting the adequacy of the explanation, I, of course, 

 say nothing. But when Prof. Cope implies that no expla- 

 rjiition is given, he makes still more manifest that which 

 is already made manifest by his mis-quotation — either 

 that he is speaking at second hand, or that he has read 

 with extreme inattention. Herbert Spencer 



Athenjeum Club, Jan. 29 



THE CHANCE OE SURVIVAL OE NEW 

 VARIETIES 



A N argument first urged by the writer of an article on 

 -^~*- the " Origin of Species " in the North British 

 Kcvicii) for June 1867, regarding the probability of the 

 preservation of a new modification or variety among the 

 descendants of a plant or animal, has of late attracted 

 much attention. It has been discussed at length by Mr. 

 Mi\-3rt, one of the ablest critics of the Darwinian theory, 

 and Mr. Darwin himself has, with characteristic candour, 

 ascribed great, and as I believe undue, importance to the 

 in'crences drawn from it. 



To some extent I agree with the remarks of Mr. Davis, 

 published in your journal of the 2Sth December last, but 

 I vfnture to think that the soundness of the argument in 

 question has not been thoroughly tested, and that it will 

 not bear close examination. The calculus of probabilities 

 is a very subtle instrument, and, even in what appear to 

 be its simpler applications, a very fallacious one, if every 

 step in the process is not carefully considered 



The reviewer started with a seemingly simple state- 

 merit of the case — '' A million creatures are born ; 10,000 

 surviv-e to produce offspring. One of the million has 

 twice as good a chance of surviving ; but the chances are 



* By way of correctirg a further misapprehension ( f Prof. Cope, I may 

 here point out that this concep'ion, in its less developed form, goes back to a 

 much earlier dale than the " Piinciplesof liiology ' to which he refers. In the 

 iVcstminsttr Kt'vieju for April 1852 (pp 49S-500), 1 have contended that 

 " tliis inevitaVIe redundancy of numbers — this constant increase of people 

 beyond the means of subsistence," necessitates the continual carrying-otiof 

 " those in whom the power of ^elf-preservalion is the least;" that all being 

 sniiject to the " increasing difficulty of getting a livmg which excess of fer- 

 tility entails.'* there is an average advance under the pressure since ' only 

 those who do advance under it eventually survive ;" and these " must be the 

 .select of their generation," There is however, in the cssiy from which I here 

 quote, no recognition of what Mr. Darwin calls "spontaneous variati n," nor 

 of that d.vt-r£t;nce of type which this natural selective process is shown by him 

 to produce. 



50 to I against the gifted individual being one of the ten 

 tliousand (at first erroneously printed 'hundred') sur- 

 vivors." The fallacy here lies in the assumption that 

 under the conditions which, according to the Darwinian 

 theory, enable natural selection to become an efficient 

 modifying agent, the chance of survival of a favourable 

 modification can be correctly represented by the ratio of 

 2 to I. 



To avoid complication let us confine the argument to 

 non-dictcious plants or self-fertilising lower animals. The 

 preservation of a new variety or modification of structure 

 depends upon two separate elements r< lated respectively 

 to growth and reproduction. The individual must reach 

 maturity, and must reproduce offspring, and for each of 

 thtse processes it must be able to overcome the obstacles 

 oftL-red by the action of other organic beings, and by ex- 

 ternal physical conditions. As a general rule we may 

 assume that the same modification does not aflect both 

 growth and reproduction, and as the main stress of the 

 struggle for existence turns on the dangers that affect the 

 early period of growth, and the difficulties attendant on 

 the production of healthy offspring, we shall sufficiently 

 illustrate the subject in hand by considering these sepa- 

 rately. 



The chance of a modified individual growing to matu- 

 rity depends upon its power of resistance to, or escape 

 from, the various hostile agencies that surround the young 

 animal or plan', whose combined influence is (by hypo- 

 thesis) such that but one out of every hundred reaches 

 maturity. Let us assume, for the sake of illustration, that 

 the most important dangers to which the creature is ex- 

 posed arise from physical conditions— such as excessive 

 drought or damp— and from other organisms, as when 

 it is the favourite food of some common animal. Now 

 let the supposed modification affect the former relation. 

 Let the modified organism be better fitted to resist 

 drought ; the result will be an enormous probability in 

 favour of its escape from a danger that may destroy nine- 

 tenths of the unmodified creatures around him, and a 

 similar argument will apply to such a modification as 

 would make the individual modified distasteful, or less 

 than usually attractive, as an article of food. In point of 

 fact, the dangers arising from external physical conditions 

 are usually far less constant in their action than those 

 arising from organ c foes, and it is quite conceivable that 

 even in the extreme case of a modification originating in 

 one single individual of a species, if it were such as to 

 give a decided advantage in that direction, the balance of 

 probability would be in favour of survival, and in case of 

 reappearance among numerous individuals in the next 

 generation, have a preponderating chance of ultimate 

 preservation. 



The application of figures to measure the advantage 

 given by a modification relating to the capacity of a species 

 for reproduction involves no less difficulty, and may lead 

 to the most various estimates of the probability of sur- 

 vi\al. A variation in a plant which should double the 

 number of seeds produceti without lessening their vitality, 

 would give an advantage of 2 to i in the chance of pro- 

 ducing offspring, but this, as the reviewer has shown, 

 would not much increase the probability of the ultimate 

 prevalence of that variety. But if the numbers of a 

 plant were chiefly kept down by such a cause as the fruit 

 beng a favourite article of food, a modification of its 

 flavour that would lead to some other fruit being pre- 

 ferred would almost certainly lead to the perpetuation of 

 the variety with modified fruit, and not only to the rapid 

 destruction of the unmodified form, but also to a reduction 

 in the prevalence of some other plant. 



For it must be recollected that the struggle for exist- 

 ence is not limited to the offspring of a single species. 

 The rivals of each organism arc all around, and the 

 chance of survival of a new variety may be enormously 

 increased if it be not only better able to resist hostile 



