Natural selection in The Origin of Species

MICHAEL

NATURAL

RUSE

SELECTION IN

THE ORIGIN

OF SPECIES

A L TH o u G H

the furore which followed the publication of Charles Darwin’s long since vanished, one of the earliest criticisms levelied against Darwin’s work is still as popular today as it was then.2 This is the criticism that the central tenet of Darwin’s evolutionary theory, ‘natural selection’ or (as he later called it) ‘the survival of the fittest’, is true solely by virtue of the fact that it is tautological. The ‘fittest’, it is claimed, must be defined in terms of survival, and thus natural selection reduces to the truism that ‘those which survive are those which survive’. The charge is one which seems to be particularly attractive to philosophers who comment on Darwin’s work. For instance, recently A. R. Manser has devoted a whole paper to showing that any evolutionary theory like Darwin’s is a quasi-theory, mainly because it rests on circular concepts. About natural selection he says that ‘there can be no independent criterion of fitness or adaptability; survival and adaptability or fitness are necessarily connected’. ’ Hence he concludes that assertions about the survival of the fittest are bare tautologies. A. D. Barker in an even more recent paper supports Manser’s interpretation and argues that ‘what constitutes fitness will obviously vary with the conditions, since there could be no single empirically isolable characteristic or set of characteristics such that any organism which possessed them would in all circumstances survive’.4 Thus he concludes that we have a real tautology here, although he does think that it is a ‘significant’ tautology. J. J. C. Smart, in a polemic directed against the possibility of laws in biology, argues that: The Origin

of Species’has

If we try to produce laws in the strict sense which describe evolutionary processes anywhere and anywhen it would seem that we can do so only by turning our propositions into mere tautologies. We can say that even in the great nebula in Andromeda the ‘fittest’ will survive, but this is to say nothing, for ‘fittest’ has to be defined in terms of ‘survival’.5 Even

Antony

Flew,

although

he goes to the trouble to show how naive are

Hist. Phil. Sci., I, no. 4 (1971). Printed in Great Britain.

3”

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Manser’s that:

conceptions

of evolutionary

biology,6

is himself prepared

to say

When employed within the context of Darwin’s theory its meaning [i.e. the meaning of the survival of the fittest] is restricted. For that theory provides no independent criterion of fitness. It is, as has very frequently but too often ineffectively been pointed out, a theory of the survival of the fittest only and precisely in so far as actual or possible survival is to be construed as the sufficient condition of fitness to survive . . . natural selection is necessarily selection onlv for exactly what at precisely the time in question it in fact takes to survive. . . .’ Although philosophers figure prominently in this attack on natural selection, they are not alone. For example, the historian Gertrude Himmelfarb agrees with these critics and claims that there are several ‘areas of life in which the principle of the survival of the fittest is questionable, or at most meaningful only in the tautological sense that the survivors, having survived, are thence judged to be the fittest’.’ However, perhaps the most explicit recent instance of this charge is to be found, amazingly, in the writings of one of today’s leading biologists, C. .H. Waddington. He writes : The meaning of natural selection can be epigrammatically summarized as ‘the survival of the fittest’. Here ‘survival’ does not, of course, mean the bodily endurance of a single individual, outliving Methuselah. It implies, in its present-day interpretation, perpetuation as a source for future generations. That individual ‘survives’ best which leaves most offspring. Again, to speak of an animal as ‘fittest’ does not necessarily imply that it is strongest or most healthy, or would win a beauty competition. Essentially it denotes nothing more than leaving most offspring. The general principle of natural selection, in fact, merely amounts to the statement that the individuals which leave most offspring are those which leave most offspring. It is a tautology.’ This charge that natural selection is tautological is a very serious charge to make-far more serious than I think some who make it realize. For example,

Flew

does not seem particularly

perturbed

about

it, and he

certainly does not seem to regard it as a reason for rejecting Darwinian evolutionary theory as inadequate. However, it seems to me that if the charge is in fact well founded then, for all the talk of ‘significant tautologies’, much of the interest and scientific worth of Darwin’s theory must be irretrievably lost. Furthermore, all the elaborate arguments that Darwin gives in support of natural selection must be quite irrelevant, since any armchair theorist could tell you that ‘those which survive are those which survive’. There can be no point at all in the massive amount of detailed observation that Darwin cites to justify his central principle. Of course,

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this is not to deny that probably every science has its non-empirical elements, but surely even the most hardened ofrationalists would blench at the thought of a supposedly empirical science whose major support was true entirely by virtue of its form alone ? Moreover, and this is the point which lifts the whole question above the level of a squabble between academics, if the charge is in fact a true one and Darwinian natural selection is indeed tautologica 1, then grave doubt must necessarily be thrown upon contemporary evolutionary theory, for it too relies upon a notion of natural selection-admittedly one which is somewhat broader than Darwin’s notion, but one which nevertheless bears too many similarities to Darwinian selection to be judged factual if Darwinian selection is analytic. lo In this paper I want to examine both the charge that Darwinian natural selection is tautological, and also the corollary that the arguments that Darwin offers in support of natural selection are irrelevant. ” To do this, I shall give a detailed critical analysis of certain sections of Darwin’s The Origin ofSpecies, and I shall attempt a reconstruction of the arguments that Darwin gives in justification of his claims about the existence of natural selection. Having performed this reconstruction, which incidentally will show how inadequate have been several previous analyses of Darwin’s arguments, I shall be able to show that natural selection is very probably true, empirical, and supported by genuine, relevant arguments with true premises. Moreover, I hope in the course of my demonstration to point out why so many people have been misled about the real nature of natural selection. No doubt some misreadings of Darwin are due to prejudice and careless attention to what he writes, but the major cause of the trouble is Darwin himself. He omits premises, he repeats premises (sometimes in slightly different forms), he has two or three arguments going at the same time, and he jumbles the order of premises and conclusions. He fights a not altogether successful battle against an illicit anthropomorphism which keeps intruding into what he writes. He spends a great deal of effort arguing first to something which he calls ‘the struggle for existence’, which he defines in an extremely slap-dash way, and which he claims is necessary for the proof of statements of natural selection. Not only does he not need to argue for the struggle for existence to get natural selection, but once having supposedly proved the existence of the struggle, he does not always use it in his proof of natural selection. Finally, Darwin offers us two different varieties of natural selection, and it is quite possible that they are logically distinct. All in all, I shall argue that Darwin gives us the, perhaps

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not uncommon, picture of a great inventor who is not very sure of how to present and defend the child which he has fathered. In order to carry out my plans, I shall divide the paper into five parts. In the first I shall introduce

and quote at length the relevant passages from

The Origin of Species. In the second I shall deal with the first stages of Darwin’s arguments and with the principle around which these revolve, ‘the struggle for existence’. In the third part I shall deal with the second stages of Darwin’s arguments and their conclusion, a statement about the existence of ‘natural selection’. Fourthly I shall discuss an objection which might be made to my analysis, and show why it is mistaken. Finally I shall show that natural selection is not tautological.

I The Arguments

in

The Origin of Species

Darwin begins his work by showing how great can be the results of selection by man, and then goes on to discuss how wide a range of variation is to be found between living things in the wild. Having done this, he is ready, in the third chapter, which is entitled ‘Struggle for Existence’, to give a preliminary version of his central argument. He writes: Before entering on the subject of this chapter, I must make a few preliminary remarks, to show how the struggle for existence bears on Natural Selection. It has been seen in the last chapter that amongst organic beings in a state of nature there is some individual variability. . . . But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. . . . How do these groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise ? All these results, as we shall more fully see in the next chapter, follow inevitably from the struggle for life. Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species . . . will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man’s power of selection.” Darwin commonly

next elaborates on his term ‘struggle calls it, the “struggle for existence’ :

for life’ or, as he more

I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including

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(which is more important) not only the life of the individual, but success in leaving progeny. Two canine animals in a time of dearth, may be truly said to struggle with each other which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent on the moisture. A plant which annually produces a thousand seeds, of which on an average only one comes to maturity, may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground. . . . In these several senses, which pass into each other, I use for convenience sake the general term of a struggle for existence.i3

Finally, Darwin gives an argument existence :

showing the source of the struggle for

A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may now be increasing, more or less rapidly, in numbers, all cannot do so, for the world would not hold them.14 Before attempting to dissect Darwin’s arguments, let us jump straight to the beginning of the next chapter in The Origin of Species where Darwin

repeats his position in slightly different

words.

*How will the struggle for existence, discussed too briefly in the last chapter, act in regard to variation? Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature. 3 I think we shall see that it can act most effectually. Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and, in a lesser degree, those under nature, vary; and how strong the hereditary tendency is. . . . Let it be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life. Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ? On the other hand, we may feel sure that any

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variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I caIl Natural Selection.” Finally,

let us note that although

Darwin

considers natural

selection

to

be the chief cause of evolutionary change, he is prepared to admit other causes, amongst which is sexual selection. About this he writes : This depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection.16 With these lengthy quotations before us, let us now try to reconstruct Darwin’s thinking in a somewhat more formal manner in order to evaluate his ideas. That there is an argument or several arguments intended here, cannot be denied. The passages are replete with such phrases as ‘follow from’ or ‘hence there must be’ or ‘can it then be thought improbable’. Consequently the sorts of questions which will need answering are ‘What are the premises of the arguments and are they true?’ ‘Are the arguments deductive or inductive and are they valid or sound?’ ‘What are the conclusions of the arguments be answered thinking.

and are they true ?‘. I doubt if these questions can fashion, but they should guide our

in any neat sequential

II The Struggle for Existence It seems clear that although Darwin is primarily concerned to demonstrate the existence of ‘natural selection’, he does not believe that this can be done in one step. He believes that what is first required

is a sub-argument

which

demonstrates that there is a ‘struggle for existence’. Unfortunately, Darwin does not give us a formal definition of this latter term, and indeed he remarks, perhaps truly but not very helpfully, that he uses it in a ‘large and metaphorical sense’. ” The grave difficulty to be encountered in understanding the term becomes apparent as soon as one realizes that it is not altogether clear whether Darwin considers the ‘struggle’ to be one for ‘existence’ at all. Although he gives obvious examples of a struggle for existence (for instance two organisms fighting to the death for food), he does state that the term includes ‘(which is more important) not only the life of the individual, but success in leaving progeny’. I8 Hence it would seem that ‘the struggle for existence’ would more properly be construed as ‘the struggle for reproduction’. Unfortunately, although this may have been

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the main thrust of what Darwin meant, elsewhere he seems to contradict this. As we have seen, in the case of sexual selection, Darwin does definitely seem to think that we have a struggle for reproduction and not for existence. However, he then goes on to say that since this kind of struggle does not lead to death, sexual selection is ‘less rigorous’ than natural selection-the implication being that natural selection depends on a struggle which does lead to death. In the light of all this, it seems that the fairest thing to say is that for Darwin, the struggle for existence is basically a struggle to survive long enough to reproduce, that is, to leave offspring, and that this is something which, if it is to be successful, usually leads to the death of other organisms (and, if unsuccessful, is usually so because of death), but not necessarily. lg Now, having looked at the way in which Darwin seems to use the term ‘existence’, let us turn our attention to ‘struggle’. Here also, it is clear that Darwin means more than just literally struggling or fighting, although he obviously includes this. A plant in the desert is not literally ‘fighting’ the desert. It is difficult to think of a neutral, non-metaphorical, term to cover all of the things Darwin intends, particularly since in certain respects the activities of organisms seem to be the very opposite of ‘struggle’. The desert plant, for example, might only be able to grow under conditions of drought. Perhaps the best way of conveying what Darwin means is to say that ‘struggle’ (for some goal) is the same kind as ‘some kind of response or activity which occurs which helps to bring about the goal, where, if it did not occur, the goal would not be achieved’. When the struggle is directed, not so much towards the attainment of a future goal, but rather towards maintaining some present state, then ‘struggle’ can be understood as ‘some kind of response or activity which occurs which helps to maintain a particular state, where, if it did not occur, the state would be lost, if not immediately, at least fairly rapidly’. Thus when one animal is fighting another for food, it is doing something to get the food and it would not get the food unless it fought. Similarly, when a plant ‘struggles’ in the desert, it is doing things to survive and if it did not do them (i.e., ‘gave up the struggle’) it would die, if not instantaneously, within afairlyshortperiod of time (certainly ‘short’ relative to the time needed for the plant to grow from a seed to full reproductive maturity). Hence, putting things together, as a translation of Darwin’s ‘struggle for existence’, we get something like ‘organisms (or groups of organisms) respond in certain kinds of ways and they must so respond in order to survive long enough to reproduce-in so doing they usually bring about the deaths of other organisms, or at least,

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the failures of others to reproduce,

and if they fail to do so, then their own

deaths probably follow’.” With this as our guide,

let us now see how Darwin

argues

to this

proposition. He begins by claiming that ‘a struggle for existence inevitably follows from the high rate at which all organic beings tend to increase’,2 i and from this it would seem that what he is offering us is an argument which is deductive in nature. Moreover, it would seem that the argument has one premise which is (Statement

I) 22

All organic

beings tend to increase

at a high rate,

and has the conclusion (Statement

2)

There

is a struggle for existence.

Hence one might conclude that one has here a simple deductive argument and that it is easy to show its exact nature. Unfortunately this is a rather shallow reading of the situation. In the first place, it is by no means obvious that Darwin intends that Statement I taken in a literal sense be a premise. Statement I claims that all organic beings tend to increase, but I think it is quite possible that what Darwin meant was, rather than that each and every organic being has this tendency, that each species of organic being has such a tendency, or possibly that other types of groups of organic beings have such a tendency, or even possibly that all organic beings taken together have such a tendency. In the sentence following the one being considered, Darwin talks of every being suffering destruction, otherwise its numbers become so great, and shortly afterwards he shows that he is thinking not so much in terms of inter-organic relationships, but rather of relationships between species and of the relationship between the whole organic world and the inanimate world, since he says that there must be ‘a struggle for existence, either one individual with another of the same species, or with the physical conditions of life’23 and then ‘although some species may now be increasing . . . all cannot do so . . .‘a24 Thus it would seem that a better premise (i.e., one which is truer to Darwin’s intentions) than Statement I is the somewhat ambiguous (Statement

3)

Organic

beings tend to increase

at a high rate;

where this could be taken to refer to each group (probably species) of organic beings or to all organic beings taken together, or most likely, to a greater or lesser extent, to both of the possibilities.

Natural Selection in The Origin of Species

Next let us turn to the question premise in Darwin’s quoted

sentence

argument.

3’9

of whether

Statement

3 is the only

I think it is clear that although

gives the impression

that

it is, the fact

the above-

that

Darwin

follows with a whole paragraph

of new points shows that it is not. What then are Darwin’s other premises ? The next thing he says is that ‘every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product’.25 There seem to be three premises here, and the first one, assuming that the reference to eggs and seeds is the same as a reference to a tendency to increase, and that the point about geometric increase is well taken (i.e., that if things go on increasing geometrically, their numbers go up without limit), seems to be something like (Statement 4) If organic beings tend to increase at a high rate then either there must be some destruction going on or the numbers of organisms go up without limit. The second and third premises in the sentence

seem to be

(Statement 5) If the numbers of organisms go up without limit then there must be enough food available now to support them. (Statement 6) There is not enough food available now to support them. Unfortunately

although

Darwin

now goes on to talk about the fact that

‘as more individuals are produced than can possibly survive, there must in every case be a struggle for existence’,26 it is clear that there are even more premises to his argument, because later he says that in the case of the organic world there can be ‘no artificial increase of food, and no prudential restraint from marriage’.27 Hence we seem to have two additional premises. First, assuming that the reference to the impossibility of an increase in food is directed towards the amount of food which would be needed to support unlimited numbers of organisms, we have (Statement 7) The amount of available artificially to support unlimited numbers; and secondly

food cannot

be increased

we have

(Statement

8)

There

can be no prudential

restraint

from marriage.

.

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Now

as the matter

stands

at the moment,

these

premises

seem

a little

irrelevant, nothing)

since Darwin has not yet said anything (and does in fact say to connect them with what has gone on earlier. Consequently,

assuming

that Darwin

did believe

Statements

7 and 8 to be pertinent

to his

argument, it is now necessary to revise some of his earlier premises, in particular Statements 4 and 5, so that these later premises, Statements 7 and 8, can be seen to be an essential part of Darwin’s whole line of thought. This can be done by revising Statements 4 and 5 to (Statement g) If organic beings tend to increase at a high rate then either the tendency to increase must be held in check by something or the numbers of organisms go up without limit; and If the numbers of organisms (Statement 10) then either there must be enough food available or the amount of available food can be increased

go up without limit now to support them artificially to support

them. Also one must have another with the prudential restraint

premise to correlate and the destruction.

the check in numbers This can be

(Statement 1 I) If the tendency to increase must be held in check by something then this must be through prudential restraint from marriage or it must be through the fact that some organisms die (presumably, die without being able to reproduce). The

task of reconstruction

draws

towards

a close, but there

still remain

two important points to be made. Both of these points seem to show that Darwin is offering us more than one argument at this point of the text. In the first place, having talked about destruction and geometrical increase, Darwin then says ‘hence as more individuals are produced than can possibly survive, there must in every case be a struggle for existence’.z8 Thus it would seem that Darwin wants first to argue to the conclusion that (Statement

I 2)

Some organisms

die without

being able to reproduce,

and then wants to use this to argue to the statement that there is a struggle for existence (Statement 2). Hence we have a pair of arguments in sequence. (In Statement I 2, as in Statement I I, I take the liberty of assuming that when Darwin talks of more being born than can survive, he is thinking in terms of survival to reproduce.)

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In the second place I think Darwin has yet another argument goingone which has as a conclusion Statement 12 (Some organisms die without being able to reproduce), but which he offers as an alternative version to the argument which we have been discussing above. The concluding sentence of the paragraph which we are analysing states that ‘although some species may now be increasing, more or less rapidly, in numbers, all cannot do so, for the world would not hold them’.29 Here, Darwin seems to be shifting his ground somewhat and now claiming that the reason why there cannot be unlimited increase in organic numbers is not so much because of restrictions on the amount of availablefood, but is rather because there are restrictions on the amount of available space. Thus we have a new argument where the premises are the same as in the previous one, except that references to food are eliminated in favour of references to space. This means that Statements 6, 7 and IO are dropped and (Statement 13) If the numbers of organisms then the world must have unlimited room,

go up without

limit

and (Statement

14)

The world does not have unlimited

room,

are added. This, then, completes the reconstruction of those arguments of Darwin which are directed towards the existence of a struggle for existence, and so let us now put everything together. There are, I claim, three arguments which are as follows. (I try to write the premises in some sort of order so as to give continuity to the various points raised by the premises.) ARGUMENT

Premise i

I

(Statement 3) : Organic beings tend to increase at a high rate. Premise ii (Statement g) : If organic beings tend to increase at a high rate then either the tendency to increase must be held in check by something or the numbers of organisms go up without limit. Premise iii (Statement I I) : If the tendency to increase must be held in check by something then this must be through prudential restraint from marriage or it must be through the fact that some organisms die without being able to reproduce. Premise iv (Statement 8) : There can be no prudential restraint from marriage. Premise u (Statement IO) : If the numbers of organisms go up without limit then either there must be enough food available now to support them or

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the amount of available food can be increased artificially to support them. Premise vi (Statement 6): There is not enough food available now to support them. Premise vii (Statement creased artificially

7):

The

amount

to support unlimited

Conclusion (Statement reproduce.

Some

12) :

of available

food cannot

be in-

numbers.

organisms

die without

being

able

to

We also have the alternative: ARGUMENT

2

Premise i (Statement 3) : Organic beings tend to increase at a high rate. Premise ii (Statement g) : If organic beings tend to increase at a high rate then either the tendency to increase must be held in check by something or the numbers of organisms go up without limit. Premise iii (Statement I I) : If the tendency to increase must be held in check by something then this must be through prudential restraint from marriage or it must be through the fact that some organisms die without being able to reproduce. Premise iv (Statement 8): There can be no prudential restraint from marriage. Premise v (Statement 13) : If the numbers of organisms go up without limit then the world must have unlimited room. Premise vi (Statement 14) : The world does not have unlimited room. Conclusion (Statement

I 2)

:

Some

organisms

die without

being

able

to

being

able

to

reproduce. Finally

we have, following

3 Premise i (Statement reproduce.

I 2)

Conclusion (Statement

2) :

on from Arguments

I and 2:

ARGUMENT

:

Some

There

organisms

die without

is a struggle

for existence.

With these formal reconstructions before us, which if they are accepted already convict Darwin of some of the faults I charged him with at the beginning of the paper, let us now turn to the task of assessing the truth of the premises of the arguments, in particular of Arguments I and 2. It

Natural Selection in The Origin of Species will be remembered increase

that Statement

3, namely that organic

323 beings tend to

at a high rate, can be taken in two senses: as referring

either to

groups (probably species), or to all beings taken together. It is fairly clear that on either interpretation the statement is true. (Obviously, if the statement is true in the first sense, then it is true in the second.) Darwin himself gives a great number of examples of species with such a tendency, and he points out that even when organisms reproduce infrequently, their numbers would be of colossal orders after a few years.30 Moreover, in the century since The Origin of Species appeared, biological investigation has served only to underline the truth of the statement and today’s biologists are as strongly committed to it as Darwin was. For example, the contemporary evolutionist J. M. Smith writes that the observation that animal and plant species, including the human species, are capable of indefinite increase in numbers in optimal conditions, is correct. . . . In a few species, such as the herring, the maximum potential increase per generation may be as much as a millionfold. However, even in species such as our own where relatively few offspring can be produced by a single pair, the potential rate of increase is very rapid.31 In view of the truth of this fact, it is somewhat surprising that T. A. Goudge, in a recent discussion of Darwinian evolutionary theory, should criticize Darwin for accepting it and, in particular, that he should criticize Darwin for using it as a premise. In his book, The Ascent of Lif&32 Goudge writes : Darwin contended that excessive reproduction, i.e. reproduction at approximately a geometric rate, is characteristic of all living things. But it is clear that the production of offspring is only excessive in relation to an imaginary world and the ‘high geometrical rate of increase’ is only attained by abolishing a real death rate, while retaining a real rate of reproduction.33 Goudge therefore concludes that ‘if the doctrine of reproduction at a geometric rate is untenable, then it cannot legitimately serve as one of the premises from which natural selection is infeered’.34 Obviously Goudge distorts grossly what Darwin wrote. Darwin’s whole point is that there is no actualgeometric increase, which increase is just what Goudge accuses him of accepting. Darwin argued that on& if organisms were unchecked would there be such an increase. This is true and, as such, is a perfectly good premise. 35 The second premise common to Arguments I and 2 is Statement g, namely that if organic beings tend to increase at a high rate then either the tendency to increase must be held in check by something or the numbers of

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organisms go up without limit. This premise hardly needs comment since it is almost trivially true. As soon as one assumes that everything has a cause

(in this instance,

assumption

that

a check

with the mathematical

has a cause),

and combines

truth that if something

the

keeps multiply-

ing then it will get bigger and bigger, the premise follows at once. This leaves just two more premises common to Arguments I and 2. First there is Statement I I, which states that if the tendency to increase must be held in check by something, then this must be through prudential restraint from marriage or it must be through the fact that some organisms die without being able to reproduce ; and secondly there is Statement 8, that there can be no prudential restraint from marriage. Now presumably by the phrase ‘prudential restraint from marriage’ Darwin does not mean anything quite so literal as abstaining from the bonds of holy wedlock. Rather he must be referring to anything which would provide a nonlethal check to a population explosion. (A check, of course, which would not be so severe as to destroy the tendency to increase; hence something like castration would be barred.) This being so, then Statement I I becomes true-indeed, like Statement g, it is pretty well trivial, since all it says is that if the tendency is checked this must either be done by lethal or nonlethal means. However the big question which must now be answered is whether Statement 8 must be true -is it impossible that there be any way of checking population numbers non-lethally without destroying the tendency to increase ? One’s first response to this question might be that such checks not only could exist, but do in fact exist, namely between humans. However, I think it is clear that in this passage which we are discussing, Darwin is not directing his attention to the human part of the organic world-indeed the whole of The Origin of Species is not really about man. Admittedly, right at the end of the work, in what must be the understatement

of the nine-

teenth century, Darwin remarks that ‘light will be thrown on the origin of man and his history’ ; 36 but in actual fact, consideration of man is reserved for a later work, The Descent of Man. Thus I think Darwin would claim that human restraints do not affect the truth of his premise, since the premise is not about humans at all. Furthermore, he might point to the fact that, even if one did include humans, their present performance need in no way shake one’s confidence in the fact that even they are capable of only a very limited degree of restraint. The failure of the Indian Government’s campaign to promote contraception widely might show that even the mildest kind ofrestraint is beyond the grasp of most humans. But setting

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aside the question of Homo sapiens, is it possible that there is non-lethal restraint in the organic world (restraint which is, of course, not caused by humans, even on other forms of life) ? My own belief is that such restraint is not possible. Consider how such restraint might come about. What one would need would be some way of systematically segregating nearly all of the sexes-although even this would be useless as far as that large part of the organic world which lacks sexuality is concerned. It is difficult to think what kinds of barriers could perform these segregations, particularly in the case of extremely mobile organisms like birds, which can fly over or around almost every natural barrier. Moreover, even if one could have such barriers, it is difficult to see how they could never lead to death. Consequently I would suggest that Darwin is most probably right in claiming that non-lethal checks to population increase could never work.37 This now brings us to the premises where Arguments I and 2 part company. Let us look first at the premises peculiar to Argument I. The fifth premise, Statement IO, states that, if the numbers of organisms increase without limit, then either there must be enough food available now to support them or the amount of available food can be increased artificially to support them. Given the fact that organisms require a finite amount of food this premise is clearly true, as is the next premise, Statement 6, that the world does not at present have enough food for an unlimited increase. Finally we have the seventh premise, Statement 7, that the amount of available food cannot be increased artificially to support unlimited numbers. Again we seem to have a true statement. Although it is certainly the case that food production could be increased drastically, it is still the case that there must be an upper limit to this increase, if only because the amount of energy coming from the Sun and already here on Earth is finite. At some point, all available sources will have been exhausted and, in the jargon of the physicists, the entropy will have reached a maximum. Turning now briefly to the undiscussed premises in Argument 2, it soon becomes apparent that they also are true. The fifth premise, Statement 13, claims that if the numbers of organisms go up without limit then the world must have unlimited room. This must be so, since organisms have finitesized bodies. The final premise, Statement 14, claims that the world does not have unlimited room, and needs no proof. Thus as a result of our investigation we are now in a position to claim that the premises of Arguments I and 2 are true (with the qualification that possibly the fourth premise does not apply to humans). Moreover, since it

Studies in History atrd Philosophy of Science

326

is quite clear that the arguments merely presumed

are in fact deductively

valid

to be so), we can now assert without further

that their joint conclusion,

Statement

I 2,

(and not argument

is also true. That is, some organ-

isms die without being able to reproduce or, in Darwin’s own words, ‘more are born than can possibly survive’. This brings us now to the final task in this section, namely a consideration of Darwin’s argument from the conclusion of Arguments I and 2 to the major conclusion that he is trying to establish at this point, an assertion about the existence of a struggle for existence. This argument we gave as Argument 3, and it has, it will be remembered, one premise, Statement 12 (Some organisms die without being able to reproduce), and the conclusion, Statement 2 (There is a struggle for existence). As in the cases of the first two arguments I think that again we are dealing with an argument where both the premise and conclusion are essentially true, but I suspect that this argument is not only deductively invalid, but that to remedy this w-ould require a far more drastic reconstruction than anything we attempted in the cases of Arguments I and 2. If we understand by ‘the struggle for existence’ something with the sense that I elucidated earlier, namely that organisms (or groups of organisms) respond in certain kinds of ways and they must so respond in order to reproduce, and that in so doing they usually bring about the deaths of other organisms, and if they fail to do so, then their own deaths probably follow, then in asserting its existence we seem to have a statement about the organic world which holds almost universally. Darwin himself gives many examples of its truth, and countless other instances spring to mind almost immediately. However, even though it is true that there is a struggle for existence (in a Darwinian sense), the struggle (or, more accurately, a statement about the struggle) does not follow deductively from a statement about the fact that some organisms die without being able to reproduce. The reason for this is that the struggle for existence gives us a possible cause or one of the possible causes for the truth stated in the premise to Argument 3, but it is not logically necessary that this be the right cause (or one of the right causes), which it would have to be if the argument were deductively valid. Suppose that the way numbers were kept in check was by some cataclysmic force of nature, periodic floods for example, and that organisms made no attempts to evade the effects of these forces, and that, further, perfect harmony existed between organisms themselves. Suppose also that survivors of these forces went ahead, living to ripe old ages, and reproducing without facing any other barriers. It could hardly be said that they ‘struggled’

.Nutural Selection in The Origin of Species either to exist or to reproduce,

and their existence

not be the causes of the deaths of other organisms.

327 and reproduction

premise that some organisms die without being able to reproduce true,

but the conclusion

that there is a struggle

would

In such a situation, for existence

the

could be would be

false. Hence Argument 3, considered as a deduction, is invalid. Now the obvious move at this point is to consider the ways in which this argument might be patched up, and there are two possible courses of action. In the first place, we might try to give reasons for suggesting that we have here, not a bad deductive argument, but a good inductive onean argument, that is, where the truth of the premises merely makes probable the truth of the conclusion. In the second place, we might try adding additional premises in order to make the argument deductively valid. However, although these are the obvious ways of tackling the problem, I am not entirely sure that either is the wisest. The reason for this is that I think we shall see shortly that it is not necessary to rescue Darwin’s argument because he does not need the conclusion, that there is a struggle for existence, to argue for his main conclusion, that there is ‘natural In addition, I think one can find some good evidence that selection’. Darwin does not always in fact use a statement about the struggle for existence to argue for the truth of the existence of natural selection. What he uses instead is the conclusion to his previous Arguments (I and I), a statement that some organisms die without being able to reproduce. In order to see if this is so, let us now go on to the second phase of Darwin’s thinking, where he uses the conclusions of the arguments that we have just been discussing, as premises for another batch of arguments.38 III Natural

Selection

As we did earlier, let us try to reconstruct Darwin’s thinking in a formal manner and, in order to do this, let us once again begin by considering the conclusion towards which Darwin is arguing. The conclusion in this case is a statement to the effect that there is ‘natural selection’. Regretfully, even though this conclusion is the lynch-pin on which his whole system is based, in discussing it Darwin displays the same kind of ambiguity which made it so difficult to pick out the exact meaning of the conclusion we discussed in the last section, for I think that, if we look carefully at what Darwin writes, we find that he offers us not one version of natural selection but two. Furthermore, I think that these versions are not merely the same thing in different words. Let us see what Darwin claims.

Studies in History and Philosophy of Science

328

In the passage

which

was quoted

from

the third

of Species, it is quite clear that he intends ‘natural to the actual survival of certain organisms (and organisms), viving

but

(or failing

rather

to the chances that

to survive).

certain

chapter

of The Origin

selection’ to refer, not actual deaths of other organisms

have

of sur-

He writes :

Owing to this struggle for life, any variation, . . . if it be in any degree profitable of that individual, and will generally be * . . will tend to the preservation inherited by its offspring. The offspring, also, will thus have a better chance oj‘ surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of NaturaI Selection. . . .3Q Again,

in the fourth chapter, when Darwin renews his discussion about natural selection, it seems at first that here also he intends that ‘natural selection’ should refer to the chances that certain organisms have in the survival and reproduction stakes. He writes: If such do occur [i.e., useful variations], can we doubt . . . that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind?40

Unfortunately, instead of now completing this passage by saying something to the effect that organisms without such advantageous characteristics (i.e., organisms with what Darwin calls ‘injurious’ variations) would not have such a good chance of surviving and procreating, and by saying that it is to these various chances that he refers when he speaks of ‘natural Darwin changes gear violently. In the very next sentence selection’, he abruptly starts to talk of the actual results that we might expect from the different chances that organisms have, and it is to these actual results that Darwin now refers when he defines ‘natural selection’. He writes : On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.4’

Thus I suggest that we find in Darwin’s writings two versions of natural selection, where in some sense the second comes about because of the first. These versions I shall call ‘Natural Selection I’ and ‘Natural Selection 2’, and they may be stated formally in the following way. Natural Selection I: Organisms with useful (or favourable) have a better chance of surviving and reproducing than with injurious variations.

variations organisms

.Natural Selection in The Origin of Species

329

.Natural Selection

2: The ‘effect’ of Natural Selection I, or the realized expectation of Natural Selection I, namely the actual preservation of those with favourable variations and the actual rejection of those with injurious variations.42

With these formal definitions laid clearly before us, we are now in a position to go on to consider the arguments that Darwin offers for them, much in the way that we considered the arguments in the last section. Before doing this, however, it will be interesting to pause for a moment and to consider why it is that here, of all places, Darwin is so infuriatingly unclear. If nothing else, one might have thought that the definition of natural selection would be stated in a precise way. One can but speculate at the true reason, but I suspect that at least part of the cause lies in the fact that, in the passages we are considering, Darwin is striving, perhaps not entirely successfully, to rid his ideas and his language of unwarranted anthropomorphic elements. As is well known, a criticism of Darwin, as old and as common as the charge that natural selection is tautological, is the claim that his work mistakenly reads human characteristics into non-human phenomena.43 That a charge like this should have been made, and indeed that the charge is not entirely without foundation, is not altogether surprising, since Darwin does quite consciously model much of what he writes on observations of human achievements and upon writings and theories which are concerned solely with man. He takes the idea of ‘natural’ selection directly from the breeders’ successes with ‘artificial’ selection, and we can see that, in the passages that we are considering, he uses the triumphs of artificial selection to bolster his case for natural selection. On top of this, there is also the fact that many of the very premises and arguments that Darwin uses are taken directly from Malthus’s Principle of Population, a work entirely about the problems of human population growth. It is for this reason that in the last section we came across such quaint (and blatantly anthropomorphic) phrases as ‘prudential restraint from marriage’. Now what Darwin’s critics claimed (and what some still do in fact claim) is that this reliance upon things human leads Darwin into reading into the inanimate world, and also into the non-human organic world, characteristics which could not possibly be other than human. In particular, the critics claim that Darwin treats natural selection rather too much like artificial (i.e., human) selection, and that either he sounds as if all organisms have conscious control over their fate, or he looks upon Nature (with a capital N) as some kind of disembodied life force, which strives teleologi-

Studies in History and Philosophy of Science

330

tally towards the perfection of organic forms by the conscious eIimination of the unsuitable. Moreover, the critics are able gleefully to quote purple passages like the following

from The Origin of Species:

Under Nature, the slightest differences of structure or constitution may well turn the nicely balanced scale in the struggle for life, and so be preserved. How fleeting are the wishes and efforts of man! how short his time! and consequently how poor will be his results, compared with those accumulated by Nature during whole geological periods! Can we wonder, then, that Nature’s productions should be far ‘truer’ in character than man’s productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship ?44 Darwin

was clearly

aware

of this criticism

of unwarranted

anthro-

pomorphism and he fought to avoid it (regretfully he did not try to avoid it by removing the above passage from The Origin of Species). In later editions of his work he tries to persuade the reader to use.the term ‘the survival of the fittest’ rather than ‘natural selection’, because he thinks that the former carries fewer human connotations than the latter.45 He also adds a short passage disclaiming any intention of finding in nature any purposeful forces. He argues that ‘in the literal sense of the word, no doubt, natural selection is a false term’,46 and he adds: It has been said that I speak of natural selection as an active power or Deity . . . [and] it is difficult to avoid personifying the word Nature; but I mean by Nature, only the aggregate action and product of many natural laws, and by laws the sequence of events as ascertained by US.~’ The last thing that Darwin wants to do is to introduce mysterious teleological forces into his evolutionary theory. It was the very presence of these which made Lamarck’s evolutionary theory so unpalatable to him.4* What I would like to suggest, therefore (although frankly it can be no more than a suggestion), is that it is because of this great concern to avoid making nature more than an aggregate of laws, that Darwin’s writing becomes so ambiguous when he introduces his major thesis about natural selection. He wants natural selection to be in some sense the cause of evolutionary change (or, at least, the thing which leads us to suspect that evolutionary change will occur)-on the other hand, he does not want the term to lead his readers into believing that there are powers in nature, or that unconscious organisms (like plants) can make conscious decisions. Thus it seems plausible to suggest that, although Natural Selection I is more directly the sort of thing that Darwin conceives of as causing or as leading one to accept evolutionary change, he repeats himself in slightly

Natural Selection in The Origin of Species different words (Le., Natural

Selection

2)

331 to emphasize

that he is trying not

to step outside the bounds of what one might call a ‘mechanistic’ To say the least, talk of certain teristics

having a better

‘chance’

organisms

with their ‘favourable’

than organisms

with ‘injurious’

position. characcharac-

teristics in the ‘struggle’ for existence (which is brought about by organisms ‘striving to the utmost to increase in numbers’49), is liable to suggest in the reader’s mind that this chance comes about either through the organisms’ own direction or through the planning of something (or someone) else. On the other hand, to talk of certain types of organism actually surviving or actually dying, seems far more innocuous-in nature things are always sorting themselves into groups without man’s help or without any conscious help at all. Hence, on this latter kind of reading, natural selection becomes just a mechanical sorting writ large, with no hint of minds directing the sorting. It is perhaps worth adding in support of the case I am trying to make that, in the later editions of The Origin of Species, not only does Darwin propose ‘the survival of the fittest’ as a substitute for ‘natural selection’, he also alters the language in which he introduces what I have called Natural Selection 2. The sole purpose of the alteration seems directed towards purging natural selection even more of undesired humanattributes. Instead of claiming that natural selection is ‘this preservation of favourable variations and the rejection of injurious variations’,50 the claim becomes that natural selection is ‘this preservation of favourable variations and the destruction of injurious variations’. 5 r It cannot be without significance that, whereas a ‘rejection’

seems to call for a conscious

decision,

a ‘destruction’

can occur entirely without a thinking agency. I shall return shortly to Darwin’s problems with anthropomorphism, and I shall try to show that, although Darwin is not entirely free from blame, he is not guilty of quite all the faults that some critics have levelled against him. At this point, however, let us turn to a consideration of how Darwin argues for the existence of natural selection; in particular, let us see how he argues for the existence of Natural Selection I. Twice in the passage from the third chapter, Darwin tells us that Natural Selection I follows from the struggle for existence. (‘All these results . . . follow inevitably$rom the struggle for life. Owing to this struggle for life . . .‘.52) However, once in this passage and once in the passage from the fourth chapter, he argues that it follows from the fact that more are born than can survive. ‘The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically

Studies in History and Philosophy of Science

332

born, but a small number can survive’ ;” and later, ‘If such do occur, can we doubt (remembering that many more individuals are born than can possibb survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ?’ * 4 Hence it would seem that there are two arguments at work here; both assert the existence of Natural Selection I as conclusion, but one uses a statement about the struggle for existence as a premise and the other uses a statement about the fact that more are born than can survive. These are not the only premises in the arguments; there are clearly other premises at work in both of them, premises which somehow take account of the variations which different organisms have. In the third chapter of The Origin of Species Darwin writes: . . . amongst organic beings in a state of nature there is some individual variability. . . But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation of the work, helps us but little in understanding how species arise in nature . . . How do those groups of species . . . arise? All these results . . . follow inevitably from the struggle for life. Owing to this struggle for lifk, any variation, however slight and.from degree projtable to an individual of any species, organic beings and to external nature, will tend will generally be inherited by its offspring. The

whatever cause proceeding, zf it be in any in its infinitel_y complex relations to other to the preservation of that individual, and

offspring, also will thus have a better chance of surviving for, of the many individuals of any species which are periodically born, but a small number can survive.55 In the fourth chapter

we find:

Can it then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations. If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the

other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. 56

In these passages I think we can distinguish four statements, two of which act as premises common to both of the arguments with Natural Selection I as conclusion, while the other two act as premises, each in one of the arguments for Natural Selection I. The premises common to the two arguments are obviously those which refer to the different variations which different organisms have, but it is clear that Darwin intends to record more than just the fact that there is variation. He notes, not only that there is variation, but that some (but by no means all) of it is in

Natural Selection in The Origin of Species

some sense ‘useful’ -that

is, it is the sort of variation

stances would lead to the survival and reproduction least, a high proportion circumstances,

333 which in some circumof its possessors or, at

of its possessors, and where, in the same or similar

the failure to possess such variation

would lead to a failure

to survive and reproduce or, at least, to fairly high failure rate. 57 Since he calls variations which work in an opposite manner to useful variations ‘injurious variations’, we seem to have the following two premises, common to both of the arguments for Natural Selection I : (Statement (Statement

15) 16)

Some organisms Some organisms

have useful variations. have injurious variations.

The other two premises, one of which occurs in the passage from the third chapter and the other which is vaguely referred to at the end of the above passage from the third chapter and which is made explicit in the fourth chapter, are hypothetical statements linking the variation mentioned in the above premises and the struggle for existence (in the third chapter) or the fact that more are born than can survive (end of the third chapter and in the fourth chapter) with Natural Selection I, the principle that organisms with useful or favourable variations have a better chance of surviving and reproducing than organisms with injurious variations. Now, remembering that we have decided that Darwin’s ‘more are born than can possibly survive’ is better understood as ‘some organisms die without reaching reproductive maturity’, we can state these two premises as follows: If there is a struggle for existence and if some organ(Statement 17) isms have useful variations and if some organisms have injurious variations, then organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations. (Statement 18) If some organisms die without being able to reproduce and if some organisms have useful variations and if some organisms have injurious variations, then organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations. It is perhaps necessary at this point to make one small comment in order to forestall possible criticism about the form and content of the statements to which I claim Darwin is committed. I have taken the liberty of deviating from the exact words that Darwin uses in order to make other things that he says formally relevant. Darwin clearly has hypotheti-

Studies in History and Philosophy of Science

334

cal statements in the passages that we are considering (‘Owing to this struggle . . . any variation . . . ;fit be . . . will tend . . .‘,58 and ‘If such do occur can we doubt that (remembering that . . .)‘59) ; however, in these statements he refers only to the virtues conferred by favourable variations and ignores the disadvantages of injurious variations. Since I think it is obvious that Darwin also intended to refer (albeit implicitly) to injurious variations -otherwise why else would he conclude by telling us that we can feel sure that injurious variations would be destroyed?-in Statements I 7 and 18 I have made the reference to injurious variations explicit and have also added a premise about the existence of injurious variations. In doing this, I do not think I am reading into Darwin more than he intended (nor does my action affect the validity of his arguments). We are now in a position to put the rest of Darwin’s First we have: ARGUMENT

arguments

together.

4

(to be found in Chapters 3 and 4) Premise i (Statement I 2) : Some organisms die without being able to reproduce. Premise ii (Statement 15) : Some organisms have useful variations. Premise iii (Statement 16) : Some organisms have injurious variations. Premise iv (Statement 18) : If some organisms die without being able to reproduce and if some organisms have useful variations and if some organisms have injurious variations, then organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations. Conclusion (Natural

Selection I) : Organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious

variations. We also have: ARGUMENT

j

(to be found in Chapter 3) Premise i (Statement 2) : There is a struggle for existence. Premise ii (Statement 15) : Some organisms have useful variations. Premise iii (Statement 16) : Some organisms have injurious variations. Premise iv (Statement I 7) : If there is a struggle for existence and if some organisms have useful variations and if some organisms have injurious

Natural Selection in The Origin of Species

variations, then organisms surviving and reproducing

335

with useful variations have a better chance of than organisms with injurious variations.

Conclusion (Natural

Selection I ) : Organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations. Finally we have: ARGUMENT 6 Premise i (Natural

Selection I) : Organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations. Conclusion

(Natural Selection 2) : Useful or favourable variations are preserved and injurious variations are rejected or, in other words, many if not most of those with favourable variations will actually survive and reproduce, and comparatively fewer of those with injurious variations will succeed. With this formalized version of the latter part of Darwin’s thinking before us, let us now ask of it the same question that we asked of the former part. Are the premises true, and are the purported links between premises and conclusions justified? We can answer at least part of the question very easily. It is clear, not only that Arguments 4 and 5 are intended to be deductive arguments, but also that as a matter of fact they are valid deductive arguments. Unfortunately the nature of Argument 6 gives rise to doubt and so I shall leave discussion of it until later. As we shall see, light will be thrown on this argument by our analysis of the problems to which we now turn; namely, the truth of the premises in Arguments 4 and 5. Consider first Argument 4. This has four premises, Statements 12, 15, 16 and 18. Statement I 2, that some organisms die without being able to reproduce, is the conclusion of Argument I and we have already shown that this is true. I think it is also clear that Statements 15 and 16 are true. That organisms vary, as Darwin says, cannot be denied, and given also the fact (as Darwin demonstrates in the first chapter of 27ze Origin) that many of the characteristics of domestic organisms have proved to have different functions, it does seem reasonable to assume by analogy that at least some of the characteristics of wild organisms would under some circumstances help their possessors; that is, their possessors would survive

Studies in Histqv

336

and Philosophy

of Science

and reproduce whereas those without such characteristics would fail to do this. Indeed, not only does it seem reasonable to make this assumption by arguing

analogically

from domestic

the results of many experiments

organisms,

in justification

but today of Statements

we can

cite

15 and 16.

To name but one example, the Peppered Moth, Biston betularia, has both a pale and a melanic (dark) version. It has been discovered (by H. B. D. Kettlewel16’) that the greatest natural danger facing these moths is that of being eaten by birds, and that these birds catch their prey by sight. Hence Kettlewell has been able to show that against light backgrounds it is the pale variety of the moth which has the better chance of surviving and reproducing, because it is the dark moths which more frequently get caught and eaten. Consequently here we have an example of the type of variation to which Darwin is referring-possession of pale wings is an aid to survival and reproduction in certain circumstances, and thus (by definition) is a ‘favourable variation’; conversely with respect to this context, dark wings are (by definition) ‘injurious variations’. At this point the critic of Darwin might agree that Statements I 5 and I 6 are in fact acceptable, but he might nevertheless object that, although they are true, given his evidence Darwin had no right to accept them. The statements are only to be accepted, the critic might claim, because of experiments such as the one I havejust cited. Darwin should be condemned because his only evidence for ‘favourable’ and ‘injurious’ variations is the variations which are chosen (or rejected) by breeders. Hence here, as before, he is guilty of unwarranted anthropomorphism. Nevertheless I think that, although this criticism does show that Darwin is working with limited evidence, it is not strong enough to merit outright condemnation of Darwin. Although some writers seem to think otherwise,61 anthropomorphism per se is not a bad thing. For example, few people would want to argue that driving spikes into an animal (e.g. a dog) does not cause the animal pain. Nearly all of us think that the animal would feel pain, and we would justify this belief by arguing from the strong similarities between dogs and humans-in particular, their physiological similarities and their behavioural similarities. This seems to me to be quite acceptable analogical argument. Where anthropomorphism goes wrong is in starting to draw positive conclusions even though the similarities between man and other organisms are minimal or non-existent. For example, the claim that plants can make decisions is clearly incorrect, because decision-making requires a brain of some sort, and this a plant does not have. Now, since Darwin has the knowledge that breeders select certain

Natural Selection in The Origin of Species

characteristics

because they perform

imate for him to argue that certain benefit

of their possessors rather

certain

337 functions,

characteristics

I think it is legit-

might function

for the

than solely for the benefit of man. Man

selects for a high milk yield in cows because it provides food for him, and it seems reasonable to suggest that, since calves drink milk (for nourishment), the milk yield in cows is of some importance to the cows themselves, Admittedly this is not very great evidence for sweeping generalizations about the survival value of all (or nearly all) organic characteristics, but it does seem to be some. Where the argument from human selection breaks down is in blanket assertions that just those characteristics which man selects are going to be just those characteristics selected in nature. Obviously, because man finds some pigeon feather pretty, one cannot argue that this feather would be of advantage to the bird in natural selection. Indeed, looking at the grotesque shapes into which man has bred pigeons and dogs, it is clear that many characteristics that man finds desirable would be fatal handicaps in the wild.62 Unfortunately there clearly are times when Darwin does fall into the trap ofjudging the value of natural characteristics too much by human standards. Perhaps he is most guilty of this in his discussions of sexual selection, where many characteristics are judged solely by human standards of beauty.63 However, at this point of his argument, where Darwin is only concerned to demonstrate the existence of natural selection (rather than to show exactly what actual characteristics natural selection selects for), he does not seem to have to rely on extreme analogies, arguing that naturally favourable characteristics are always those which are humanly favourable. Nor in fact does he do so. Thus I would suggest that, whilst Darwin does not offer us much evidence for Statements

I

5 and 16, offering

us rather

the task of finding evidence

for the Statements, it seems a little unfair at this point to accuse him of unwarranted anthropomorphism. This now brings us to Statement ~8, namely that, if some organisms die without being able to reproduce and if some organisms have useful variations and others have injurious variations, then those with useful variations have a better chance of surviving and reproducing than those with injurious variations. Here the problems of analysis become very difficult, since Darwin does not spell out in any precise manner (or imprecise manner for that matter) what exactly he means by ‘chance’ in this context. Consider for a moment the hypothetical world situation which I imagined earlier in the paper, namely, that some cataclysmic force wiped out numbers of organisms regularly and that there was no defence offered

Studies in History and Philosophy of Science

338

or possible against this force. Now if this were the case it might also be the case that the antecedent of Statement 18 was true, namely, that it was indeed and

a fact that some organisms

that

under

certain

die without

circumstances,

which

being able to reproduce are,

incidentally,

never

realized, certain characteristics actually possessed by organisms would ensure the survival and reproduction of their possessors, and lack of such characteristics (i.e., possession of other characteristics) would lead to an early death. Given all these suppositions, would one want to say that Statement 18 was true or false? I think, depending on the interpretation that one gives to the word ‘chance’, one’s answer could go either way. One might argue that even if my hypothetical world picture were realized, so long as not all are surviving, it would still be proper to talk of certain organisms having a better ‘chance’ of surviving and reproducing-that the circumstances which would convert this chance into a reality never occur makes no difference to the logic of the situation. Here one would be holding what one might call an a priori notion of chance, rather like someone who decides that a penny has a 50 per cent chance of coming up heads when tossed, and who holds to this belief even if for some reason the penny can never be tossed.64 If one interpreted ‘chance’ in this way, then not only is Statement 18 true, but it would seem that it is analytically true are no circumstances, actual or possible, in ( i.e., tautological)-there which one would allow Statement 18 to be false, and hence its truth-value is not a matter of empirical fact but is a function solely of the way in which the terms in it are defined. It is necessarily true because, given the antecedent conditions, by virtue of what one means by ‘chance’ the consequent must hold. On the other hand, given my hypothetical world picture, one might decide that Statement 18 is false. Even though in certain unrealized circumstances the characteristics of certain organisms may lead to survival and reproduction (and lack of them may lead to death), if such circumstances could never occur one might think it pointless to talk of such organisms having a better ‘chance’ of surviving and reproducing. One might require that some of the required circumstances be realized before one talks of ‘chances’. Here one would have something that might be called an a posteriori notion of chance, rather like someone who refuses to assign probabilities to a penny’s chances of coming up heads until the penny has been tossed a number of times.65 Clearly in this instance Statement 18 is being taken as synthetic, since it could be false, and to know its truth one must know certain things about the world, in particular

Natural

Selection in The Origin of Species

339

that the kind of world situation which I have hypothesized It would seem therefore

does not occur.

that there are two ways in which one can take

Statement 18, depending on how one reads ‘chance’. In the first, Statement 18 is analytic, and in the second, Statement 18 is synthetic and is true only if certain circumstances (where the potential usefulness of characteristics can be put to work) are realized. These circumstances need not always be realized, but they must be realized sometimes. The obvious question which springs to mind is whether these circumstances are actually realized; that is, is Statement 18, although synthetic, true? I think it is a fairly reasonable assumption that such circumstances are realized and thus that the synthetic version of Statement I 8 is indeed true. For a start, looking at the matter rather negatively, although one does get some cataclysmic forces of the type I have hypothesized above-floods, fires, earthquakes, droughts and so on-it is certainly not the case that they are so widespread that all organismic attrition can be attributed to them, and secondly, from a more positive viewpoint, there is good evidence that many of the types of circumstances where particular characteristics are able to play an important role in survival and reproduction do occur repeatedly throughout the world. For instance, the types of circumstance discussed above, where pale-winged moths have a better chance than dark-winged moths, often occur in nature. Kettlewell has clearly demonstrated that rural areas, where industrial pollution does not blacken buildings and trees, are just such kinds of circumstance. 66 Hence it would seem that it is reasonable to accept Statement 18, even though it is interpreted synthetically. In the light of this discussion, we can now start to put things together. In particular we have now got to the point where we can infer that, since *Argument 4 is deductively valid and since all of its premises are true, its conclusion Natural Selection I is also true. This holds whether we take Statement

18 to be analytic

or synthetic

although,

clearly,

the way in

which we take Statement 18 will affect the way in which we take the conclusion of Argument 4. If Statement 18 is considered analytic, then ‘chance’ in Natural Selection I is understood in what I have called an (L priori manner, that is to say, the fact that organisms with useful variations have a better chance of surviving and reproducing does not imply that such organisms ever do survive and reproduce. If Statement I 8is considered synthetically true, then ‘chance’ in Natural Selection I is a posteriori and the truth of Natural Selection I does have implications about the actual survival and reproduction of organisms. Obviously, as we shall see almost immediately, since Natural Selection I is the only premise of Argument 6,

Studies in History and Philosophy of Science

340

the way in which one interprets Natural Selection consequences for the way in which one should evaluate However,

before turning to Argument

briefly at the sister to Argument

I has important Argument 6.

6, let us pause a moment and look

4, namely,

Argument

5. This latter is the

same as Argument 4 except, where 4 has ‘some organisms die before they are able to reproduce’, 5 has ‘there is a struggle for existence’. Now I have suggested above that, although Darwin justifies the claim that some organisms die before they are able to reproduce, he has failed to do the same for the existence of a struggle for existence. But I have also suggested that, despite this omission, other considerations lead one to accept as reasonable the fact that there is indeed a struggle for existence in a Darwinian sense. Consequently I would suggest without further argument that, since Argument 5 runs parallel to Argument 4 with the (true) ‘there is a struggle for existence’ substituted for the (true) ‘some organisms die exactly the same analysis that was before they are able to reproduce’, applied to 4 can be applied to 5. In particular the counterpart to Statement 18, namely Statement I 7, can be taken as either analytically or synthetically true, and hence the conclusion (which is the same for 5 as for 4, i.e., Natural Selection I) is justified by Argument 5 although, as in the case of Argument 4, there are two ways in which Natural Selection I can be taken (the same two ways as in Argument 4). This brings us to the final stage of our analysis of Darwin’s thought, namely, a consideration of Argument 6. Again let us ask our usual questions, namely, whether the premises are true, whether the purported links between premises and conclusion are all that is claimed for them, and whether the conclusion is true. As far as the first question is concerned, since the only premise in Argument 6 is Natural Selection I, we can answer immediately that the premises are indeed true. The second question is more difficult to answer. Given that the link between premise and conclusion is strong, there are two possibilities open. Either the argument is deductiveiy valid, or the argument is a strong inductive one, the conclusion of which is very likely to be true (although it is logically possible that the conclusion is false). Consequently the question which faces us is whether Argument 6 is deductively valid, a strong inductive argument, or neither. I would suggest that the answer depends on the sense in which one takes Natural Selection I. Suppose first that one understands ‘chance’ in Natural Selection I in an a priori sense. Given this conception of Natural Selection I, does it follow that Natural Selection 2 (the conclusion of Argument 6) must

Natural

occur?

Selection in The Origin of Species

34’

It is clear that it does not since, if none of the circumstances

which the favourable

variations

in

can go to work ever occur, although we can

speak of the possessors of such variations

as having

a better

‘chance’

of

surviving and reproducing, it will not be the case that these necessarily will be the ones to survive and reproduce. Moreover, given the right kind of cataclysmic forces, it might be that all those with favourable variations get eliminated and those with injurious variations are the only ones which do in fact go on to survive and reproduce. In this kind of situation we would have Natural Selection I true and Natural Selection 2 false, and hence Argument 6 cannot be deductively valid. However, suppose now that one understands ‘chance’ in Natural Selection I in an aposteriori manner. This does presuppose that some of the right kinds of circumstances do obtain and, given this, there must be a survival and reproduction of those with favourable variations (not, it should be noted, the survival and reproduction of every organism with favourable variations, but at least some). But this survival and reproduction of those with favourable variations and similar failure of those with injurious variations is Natural Selection 2, and thus we can affirm that, given Natural Selection I (with ‘chance’ taken as aposteriori), Natural Selection 2 follows as a deductive consequence. Therefore Argument 6 is deductively valid if ‘chance’ in Natural Selection I is taken as a posteriori, but not if ‘chance’ is taken as a priori. Where does this now leave Argument 6 if ‘chance’ is taken as a priori? Does it mean that it is worthless? I think not. There are two ways in which it could be taken. In the first place it might be considered as a deductive argument, invalid as it stands, but with another premise implicit, one which does affirm the existence of the right kinds of circumstances, and one which would make the argument deductively valid. In the second place it might be considered not as a deductive argument at all, but as an inductive one where, given the premise Natural Selection I, it is claimed that it is reasonable to accept the conclusion Natural Selection 2, but where, on the information given, it could be that Natural Selection 2 is false whereas Natural Selection I is true. Frankly, it does not seem to me to be a matter of great importance which course of action is taken-either seems to do what is needed. The important point to notice is that, if ‘chance’ in Natural Selection I is taken to be a priori, then Natural Selection 2 cannot be deductively inferred from it alone. This means that, considering now Argument 6 in conjunction with Argument 4, it is impossible to go in a valid deductive manner straight from Statement 12 (some organisms die before being able to

Studies in History and Philosophy of Science

342

reproduce) and Statements 15 and 16 (some variations and others have injurious variations) Natural

Selection

2,

without

making

organisms have useful to the conclusion of 6,

another factual

assumption.

If one

merely adds an analytic statement to the premises of Argument 4, then ‘chance’ in Natural Selection I is a priori and one must add a factual premise to Argument 6, or just consider the argument as inductive. The only way to avoid this is by making ‘chance’ aposteriori, and the way to do this is by making the additional premise in Argument 4 (i.e. Statement 18) synthetic, that is, factual. Exactly similar considerations apply when one considers Argument 6 in conjunction with Argument 5. Nevertheless, having said all this, I have earlier given reasons to suggest that it is reasonable to accept the factual assumption which is required to go from the fact that more are born than can survive (or struggle for existence), and the existence of variation of the right kind, to Natural Selection 2; at least, I have suggested that it is reasonable to accept Natural Selection I when ‘chance’ is interpreted in an a posteriori manner. Since a similar factual assumption seems to be required in Argument 6, where ‘chance’ in Natural Selection I is held to be apriori, it would seem in consequence that it matters not which of the above discussed paths one takes to get to Natural Selection 2, for they are all legitimate. This, of course, means that it is reasonable to accept Natural Selection 2 as truein other words, it means that Darwin’s major conclusion has been demonstrated. My task of reconstructing Darwin’s arguments is now completed. I hope that I have convinced the reader that beneath the surface of what Darwin writes there are good arguments to be found. In particular, I suggest that there are arguments

with true premises,

which lead one

eventually to a version of natural selection which could have marked evolutionary consequences. To be explicit, this version of natural selection (which I have called Natural Selection 2) follows from the arguments which I have labelled

I,

4 and 6 and also from

2,

4 and 6.67 However,

in

concluding this section of the paper, let it be noted that, if my analysis of Darwin is correct, he stands convicted of every charge which I laid against him in the introduction. He omits premises, he repeats premises, he has two or three arguments going at the same time. He has trouble with the anthropomorphic elements in his ideas and, although he is perhaps not as guilty of arguing illicitly from human characteristics to nonhuman phenomena as some would have it, he never really seems to break entirely free from wrongly reading human attributes into nature. He

JVatural Selection in The Origin of Species

introduces

the principle,

define it properly,

‘the struggle

343

for existence’,

but then he fails to

he does not argue for it very well, and sometimes

fails to use it in his argument

for natural

selection.

Finally,

he

quite without

acknowledgment, he introduces two versions of natural selection, and leaves the reader to sort out for himself how he is arguing for them.6* In short, although I shall soon try to show that Darwin’s conclusion is not the tautology many claim it is, one can hardly wonder that his writings have generated so much confusion. IV Is ‘The Struggle

for Existence’ Really

Unnecessary?

Before using the results of the last two sections in order. to show that a statement affirming the existence of natural selection is not a tautology, it will perhaps be as well to answer a charge which might be brought against my interpretation of Darwin (rather than against Darwin himself). This charge can be formulated somewhat as follows. ‘You have argued, correctly, that Darwin does not prove that there must be a struggle for existence (in the sense that he means this phrase). However, you have also argued that a struggle for existence is not needed in the argument for Natural Selection 2. This is mistaken for the following reason. Natural Selection 2 presupposes not only that the survival and reproduction of organisms can be a function of their characteristics, but that the survival and reproduction actually is a function of their characteristics-this is what the extra factual assumption (like Statement 18) is all about. However, if this point is conceded, then it is being admitted that the cause of the fact that more organisms are born than survive (i.e., that many organisms

die before reaching

reproductive

maturity)

is not just a collec-

tion of random cataclysmic phenomena of the type that you supposed to show that a struggle for existence is not entailed by Darwin’s premises, but is at least partially some sort of systematic process which is due to the particular characteristics which organisms have. But surely, this is thevery thing to which Darwin referred when he talked of a “struggle for existence” -he did after all, as you yourself have admitted, mean much more by the phrase than literally “fighting” for existence.’ I think this criticism is a strong one but, whilst I would admit that it does show that Natural Selection 2 presupposes that there are other causes of organic elimination than random cataclysmic phenomena, causes which are linked to the characteristics of the organisms themselves, I would still deny that Natural Selection 2 presupposes a Darwinian struggle for

Studies in History and Philosophy

344

existence-at

least, I would deny it so long as one is not prepared

of Science

to widen

the scope of ‘struggle for existence’ so that it includes any systematic organismic attrition where the choice of those which go on living is a function

of the characteristics

of organisms

(a widening

which

I do not

think is countenanced by what Darwin says about the struggle for existence). The problem is whether one can conceive of a situation where there is organismic attrition which is a function of the organisms themselves and which would serve as a foundation for Natural Selection 2, but which would clearly not be a struggle for existence. If one can conceive of such a situation (remember one does not have to show that it is at all likely, just that it is logically possible), then one has shown that a struggle for existence is not essential in the argument for Natural Selection 2. Consider the following situation. Suppose all organisms loved each other and that no organism would ever dream of taking the life of another, but suppose also that there was a Dreadful Divine Being who periodically killed great numbers of organisms, the choice of which he killed being a function of the characteristics of the organisms themselves-suppose for example he always killed red and green organisms (and only these). In such a situation, I think one could say that a yellow skin would be a favourable characteristic, and there would be Natural Selection 2 with the yellowskinned being preserved. A critic might object to this hypothesis, demanding that one’s causes be kept in the natural realm or claiming that the idea of God (in the above sense) is logically absurd, but, even if one grants these objections, one can see without much difficulty how the Divine Being might be replaced by some kind of human intelligence. One could have a human intelligence (or intelligences) doing some choosing on the basis of organismic characteristics, and all other deaths (the majority) due to cataclysms. It should be remembered that Natural Selection 2 does not rule out the existence of* any cataclysmic organism-destroying phenomena, it just denies that all death is due to such phenomena. Again one would have Natural Selection 2, this time without supposing a God, but still without a struggle for existence. _Apersistent critic might still complain, this time saying that the whole point of ‘natural selection’ is that it is natural. It is distinguished from artificial selection precisely because there are no human agencies at work, agencies which are supposed in the above hypothesis. However, even when one avoids this criticism, one can still suppose Natural Selection 2

-Natural Selection in The Origin of Species

345

without a struggle for existence. Pretend that, rather than a struggle for existence, there is either a struggle for dominance, or, more extremely, a In the case of a struggle for dominance, struggle for non-existence. organisms are goal-directed towards having control over large numbers of other organisms (and since they want as many slaves as possible they look after them carefully)-in struggling for dominance many get killed and those which succeed owe their success in part to their own characteristics. I really do not think that this is the kind of situation covered by Darwin’s struggle for existence, for it could be the case that mere survival and reproduction would be easy (so long as one were prepared to accept serfdom), and yet we would have Natural Selection 2. In the case of a struggle for non-existence, organisms normally live in perfect harmony and some of them reproduce. However, at periodic intervals, lemming-like, they commit mass suicide-for example, all land creatures walk out to sea. Organisms really ‘struggle’ to do this and will try to circumvent obstacles put in their way, but some fail to commit suicide because they do not have the required characteristics-for example, their sense of direction fails to lead them to the sea. After a while the suicide urge wears off and those remaining live in harmony, happily reproducing, once again. Here it would be very odd to talk of a ‘struggle for existence’, and yet we would have Natural Selection 2. Since none of Darwin’s other premises rules out the possibility of a struggle for non-existence-for example, it could hardly be called ‘prudential restraint from marriage’-1 suggest that my original claim still stands : the existence of a struggle for existence is neither proved by Darwin nor needed by him. V Is Natural

Selection Tautological?

Thanks to our analysis of Darwin’s arguments we are now in a position to show, without any difficulty, that Darwin does not conclude with a tautology; that is, contrary to what the critics sometimes claim, his conclusion is not merely a restatement of one of his premises, which premise is but a definition of what we mean by ‘the fittest’. Darwin, it will be remembered, talked of ‘natural selection’ in an ambiguous way. In particular, it has for him two major senses, and these are Natural Selection I, namely that those organisms with useful variations have a better chance of surviving and reproducing than organisms with injurious variations, and Natural Selection 2, that favourable variations are preserved and injurious variations rejected ; that is, that at least some with favourable variations

Studies in History and Philosophy of Science

346 actually survive and reproduce.

Also it will be recalled,

there are two ways

in which we could take ‘chance’ in Natural Selection I, a priori and a posteriori. In the case of a priori chance we do not presuppose that some of the circumstances

where the favourable

variations

can take effect actually

obtain; in the a posteriori case we do presuppose that some such circumstances obtain. Now, if the critics are right, one or more of these versions of natural selection is tautologicalactually, if the critics’ charges are to have any punch, then Natural Selection 2 in particular is going to be tautological (since, after all, this is the version of natural selection which really counts-all else is just a stage on the way to it). However, I would suggest that, far from its being the case that one or more of these versions are tautological, it is rather the case that none of them are. Consider first a statement about Natural Selection I with ‘chance’ taken in an a posteriori manner. This asserts the existence of certain circumstances where favourable variations could take effect. Should these circumstances not obtain, and it is not logically necessary that they do so, then this sense of natural selection would be false. This should be impossible if this sense of natural selection were tautological, since the truth value of tautologies is independent of matters of fact. Consider next Natural Selection I, with ‘chance’ taken in an a priori manner. The truth of this is independent of the circumstances on which the truth of Natural Selection I (a posteriori) depends, but it is still dependent on the truth of some matters of fact. Were there no struggle for existence, or were it not the case that more were being born than can possibly survive and reproduce, then organisms with favourable characteristics would not even have a better a priori chance. Darwin quite emphatically draws attention to the struggle (and differential survival) when introducing talk of ‘chances’, pointing to the fact that these chances presuppose either the former or the latter. Hence here also this version of natural selection cannot be tautological, since matters of fact could make it false. Finally consider Natural Selection 2. As in the case of Natural Selection I (a posteriori), were none of the circumstances in which favourable variations could take effect to obtain, and were the forces actually eliminating organisms (against which there was no defence offered or possible) to wipe out all those with favourable variations but not those with injurious variations, we would have no Natural Selection 2. Obviously none of these antecedent possibilities is ever likely to be actually realized, but logically speaking they could be realized and, since that would make Natural Selection 2 false, it cannot possibly be tautological. In other words, although all senses of natural selection are true, their truth

Natural

Selection in The Origin of Species

stems from the way the world is, not from the form of the sentences. the charge of analyticity Finally,

347 Thus

fails.

let us see if we can pinpoint

the precise place where people are

led astray, and where they start arguing that natural selection is tautological. As I have pointed out, I think that the great difficulty that people have with Darwin’s ideas is a direct function of the ambiguities which I have discussed earlier in the paper. However, the thing which seems actually to trigger the charge that natural selection is tautological is an incorrect understanding of the role played by ‘fitness’ in Darwin’s thought. As soon as one identifies the fittest organisms with those which are bound to survive, as for example Flew does when he says that the Darwinian guarantee is ‘that it is always the fittest who have survived, the fittest who do survive, and the fittest who will survive’,6g the tautology follows at once-those who survive are those who survive. Clearly the fittest organisms are not necessarily all and only those who survive. What then are they? The most reasonable answer seems to be that they are those organisms with fuvourable or useful variations, and the unfit are those with injurious variations. But remember now what favourable variations are. These are variations where, given a struggle for existence, or at least the fact that more are born than can possibly survive, in certain circumstances (i.e., environments) a certain proportion of those which possess them will survive. (One could, I suppose, set up the circumstances where all or nearly all would survive, but then, of course, the chances of their ever obtaining would become correspondingly more remote and one would perhaps not be justified in asserting that such circumstances would ever obtain.“) Now obviously it is analytically true that a proportion of those with favourable variations (Le., the fittest) are those which would survive and reproduce in the kind of situation just envisaged, but this analyticity, far from being troublesome, is just what is expected.

One has here a deJinitionof what is meant by

the term ‘favourable characteristic’, and all definitions are analytic since they are true by fiat. For example, there can be no exceptions to ‘isosceles triangles have two sides equal’ because this is just what we mean by ‘isosceles’ -similarly there can be no exceptions to ‘a certain proportion of organisms with favourable characteristics survive and reproduce under certain specified conditions and that proportion is higher than that for injurious variations’ because this is just what we mean by ‘favourable’ and ‘injurious’. But because there is this definition it does not mean that there is a crippling tautology at the heart of Darwinian theory. None of the versions of natural selection is just a restatement of this definition-in

Studies in History and Philosophy

348

particular,

none of them guarantees

characteristics.

Natural

Selection

I

of Science

the survival of those with favourable (in either form) just talks of the ‘chance’

of such organisms surviving and reproducing, and Natural Selection 2, although it does claim that organisms with favourable variations will survive and reproduce, could be false, and furthermore, even if it is true, does not claim that all and only those with favourable variations will survive and reproduce-just that some will, enough to ensure the preservation of these variations for future generations. Thus we see why the charge of analyticity, not surprising in the light of the ambiguity of Darwin’s writings, falls to the ground. Darwin is guilty of many faults, but his conclusions about natural selection are not trivial-rather, they are true, factual, and supported. Cniversit_y

ofGuelph NOTES

i All references to ‘The Origin of Species in this paper are to the variorum text. edited by M. Peckham (Philadelphia, 1959). Unless stated otherwise, I refer by ‘Darwin’ to the first edition of The Origin of Species. s I should like to thank Alex Michalos, Hugh Lehman, the editors and referees, for commenting on earlier versions of this paper. ’ ‘The Concept of Evolution’, Philosophy, 40 (rg65), 18-34. 4 ‘An Approach to the Theory of Natural Selection’, Philosophy, 44 (1g6g), 274. 5 Philosophy and Scient$c Realism (London, tg63), 59. s ‘The Concept of Evolution: A Comment’, Philosophy, 40 (rg65), 70-j. ’ Evolutionary Ethics (London, x967), 13-14. * Darwin and the Dnrwinian Revolution (New York, Ig6zj, 316. 9 The Strategy of the Genes (London, 1g57), 64-5. to Most of Darwin’s critics realize this, and are only too happy to condemn contemporary evolutionary theory also. it Irrelevant in the sense that it does not matter what the truth-values of the premises are. The critics who hold that statements about natural selection are tautological could concede (indeed, would have to concede) that arguments asserting the existence of natural selection as conclusion are trivially valid. is Darwin, 14.4: 4-145: 15. It was in the fifth and sixth editions that he added, ‘But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient’ (Darwin, 145: 15: I : e). t3 Darwin, 146: 25-r47: 32. “Darwin, 147: 33-147: 37. ts Darwin, 163: 4-164: 13. I6 Darwin, 173: 65-174: 66. t’ Darwin, 146: 25. is Darwin, 146: 25. Since Darwin is so difficult to follow, throughout this paper I shall repeat selected sentences so that the reader may have the relevant passage immediately before him. All italics are mine. r9 It is commonly argued today that Darwin was obsessed with the fact of death, to the complete exclusion of the fact of reproduction. See G. G. Simpson, The Major Features of Evolution (New York, tg53), 138. I hope my discussion puts the matter in a fairer light.

Natural

Selection in The Origin of Species

349

2o I am trying, in this analysis of ‘struggle for existence’, to put across in an informal manner the notion, much discussed recently by philosophers and others, of ‘goal-directedness’. For a detailed but clear discussion of this notion see E. Nagel, Ihe Structure of Science (London, I g6 I), esp. chapter 12. Unfortunately I think Nagel fails to recognize all the subtleties associated with goal-directed systems in biology-for a discussion of this point see my paper, ‘Functional Statements in Biology’, Philosophy of Science (forthcoming, March 1971). 21 Darwin, 147: 33. 22 In order to help the discussion I shall number each statement which acts as either a premise or a conclusion in one (or more) of Darwin’s arguments. z3 Darwin, 147: 35. *4 Darwin: 147: 37. *5 Darwin, 147: 34, 26 Darwin, 147: 35. ?’ Darwin, 147: 36. ‘* Darwin, 147: 35. *9 Darwin, 147: 37. 3o Darwin, 147: 38-150: 62. 3 1 The Theory of Ez~olution (Harmondsworth, I 958)) 33. 32Toronto, 1961. 33 Goudge, 107-8. 34 Goudge, 108. 35 K. K. Lee makes a similarly mistaken criticism of Darwin. See his ‘Popper’s Falsifiability and Darwin’s Natural Selection’, Philosophy, 44 (1g6g), 296. 36 Darwin, 757: 257. 37 This is not to deny the widespread fact that many species of organisms have developed ‘feedback’ mechanisms which regulate their reproductive rate according to their environmental conditions-the more food or space that there is the more rapidly such organisms reproduce (and vice versa). These phenomena do not seem to be counter-examples to Darwin’s premise, first, because ultimately they are maintained in certain populations because other populations without them perish and, secondly, because such mechanisms seem to violate the proviso that Darwin stipulates in claiming the truth of his premise, namely that they seem to limit the tendency to increase. It should also be noted that such feedback mechanisms themselves often work only by killing. For example, guppies maintain a population balance by eating their surplus young. For a detailed discussion of this and like examples see V. C. Wynne-Edwards, Animal Dispersion in Relation to Social Behaviour (Edinburgh, 1962). 38 If the major claims of my analysis in this section are well taken, then three earlier analyses of Darwin’s arguments must be classed as pitifully inadequate. Sir Julian Huxley writes: ‘Darwin based his theory of natural selection on three observable facts of nature and two deductions from them. The first fact is the tendency of all organisms to increase in a geometric ratio. . . . The second fact is that in spite of this tendency to progressive increase, the numbers of a given species actually remain more or less constant. . . . From these two facts he deduced the struggle for existence’ (Evolution: The Modem @zthesis (London, 1g42), 14). A. G. N. Flew gives an almost identical analysis, arguing that geometric ratio of increase plus limited resources for living yield a struggle for existence, although he does admit that this is perhaps not a rigorous formulation of 1g5g), Darwin’s argument (‘The Structure of Darwinism’, Jvew Biology, 28 (Harmondsworth, 28). K. K. Lee gives a similar account (ofi. cit., note 35, 295). I suggest that not only do all of these authors omit essential premises but they are unaware of what can be validly deductively inferred from even an augmented set of premises. sg Darwin: 145: 13-145: ~5. 4o Damin, 164: II. 41 Darwin, 164: 12-164: 13. 4z Darwin talks as though Natural Selection I were the cause of Natural Selection 2, but strictly speaking it seems odd to talk of ‘chances’ as being ‘causes’. Chances are things which lead you to expect other things, but they do not seem actually to bring about the other things (as do causes). M:hy Darwin talked in this way I shall discuss in the immediately following paragraphs.

350

Studies in History and Philosophy of Science

‘s G. Himmelfarb makes this complaint repeatedly in op. cit., note 8: see particularly section V, ‘Analysis of the Theory’. 44 Darwin, 168: 37-168: 39. Quoted by Himmelfarb, op. cit., 313. 4s In his private correspondence he makes clear that this is the reason for the change. See, for example, the letter to Lyell, 28 September 1860, in Life and Letters (London, 1887), vol. 2. 46Darwin, 165: x4:5:cande. 47 Darwin, 165: 14: 6-g: c. 48 Many people have expressed surprise that Darwin should have been so violently opposed to the ideas of Lamarck. See for example, C. D. Darlington, Darwin’s Place in History (Oxford, I g6o), 62. After all, it is argued, in later editions of Ihe Origin ofSpecies, in order to counter criticism, Darwin began to rely more and more on the process which today bears Lamarck’s name; namely the inheritance of acquired characteristics. In actual fact, Darwin was never opposed to this process (which was, incidentally, but a very small part of Lamarck’s theory)-like most other people of his day, Darwin accepted it as being fairly obviously true. Darwin’s opposition was to the vitalistic element of Lamarck’s thinking, which was a very large part of Lamar&s theory. 49 Darwin, 150: 60. 5o Darwin, 164: 13. st Darwin, 164: 13: e. 52 Darwin, 145: x2-145: 13. 53 Darwin, 145: 14. s4 Darwin, 164: I I. 55 Darwin, I++: 5-144: 7, and 145: I r-145: 14. 56 Darwin, 164: 10-164: 12. j’ Modern evolutionists are happy to characterize as ‘favourable’ any variation which can give its possessor just a slight edge in the survival stakes, but, for Darwin, it seems that a favourable variation leads, in the right circumstances, to a high survival rate, although I do not think Darwin believed that all with favourable variations would in certain circumstances necessarily survive-just a good proportion. He constantly refers to the slight advantages conferred by favourable variations. s* Darwin, 145: 13. ” Darwin, 164: II. so ‘Selection Experiments on Industrial Melanism in the Lepidoptera’, Heredily, 9 (Ig55), 323. 61 Himmelfarb certainly gives the impression that anthropomorphism is always to be condemned. ” I discuss, in much more detail, the whole problem of when it is legitimate to argue from human selection to natural selection in my paper, ‘Confirmation and Falsification of Theories of Evolution’, .%ientia, 104 (rg6g), 329-57. s3 Even here, Darwin is not necessarily on the wrong track. Modern evolutionists are prepared to take quite seriously notions that human standards of beauty and animal standards are not totally dissimilar. See, for example, Th. Dobzhansky’s discussion of the mating displays of bower birds, in Mankind Evolving (New Haven, tg62), 215. s4 This notion of chance which I call (I priori seems similar, if not identical, to the classical or Laplacian notion of probability. ” This a posteriori notion of chance is similar, if not identical, to von Mises’s relative frequency notion of probability. For a good discussion of various notions of probability see A. C. Michalos, Principlesoflogic (Englewood Cliffs, tg6g), esp. chapter 5. H. Lehman suggests that one must, or at least ought to, interpret ‘chance’ as used by Darwin in this aposteriori manner; however, I think one could also take it in an a priori manner. See H. Lehman, ‘On the Form of Explanation in Evolutionary Theory’, Iheoria, 32 (rg66), 14-24, esp. 18. s6 Conversely, he has been able to show that where there is heavy industrial pollution, this is the kind of circumstance where dark wings are a favourable characteristic. ” Again I can onlv envy the ease with which Huxley, Flew and Lee sail through the second stages of Darwin’s arguments. Huxley writes: ‘Darwin’s third fact of nature was variation: all organisms vary appreciably. And the second and final deduction, which he deduced from the first deduction (struggle for existence) and the third fact, was Natural Selection’ (Huxley, op. cit., note 38, 14). Flew and Lee similarly claim that the struggle for existence plus variation yields

.Natural Selection in The Origin of Species

35’

natural selection. This time they not only miss out premises, add an unnecessary premise (struggle for existence), get a premise quite wrong (one needs fauourable variations, not just variations), construe incorrectly the relationship between premises and conclusion, but they also ignore shades of meaning in Darwin’s ‘natural selection’, so one is not really sure what they think the conclusion is. I am glad that others feel uncomfortable with Flew’s reconstruction of Darwin; see D. L. Hull, ‘What Philosophy of Biology is Not’, TheJoumolfor the History of BioloQy, P (x969), 241-68, esp. 253. ‘* I think there is evidence in what Darwin wrote for yet another notion of natural selectionone which follows from Natural Selection z, together with the right premises about inheritance, and which refers to the transmission of favourable characteristics to the offspring. In the third chapter, Darwin in talking of natural selection claims that certain characteristics ‘will tend to the preservation of that individual and will generally be inherited by its o&ring’ (145: x3), and in the summary at the end of the fourth chapter he writes: ‘But if variations useful to any organic being do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tendto produce offspring similarly characterized. This principle of preservation, I have called, for the sake of brevity, Natural Selection.’ (271: 385-271: 386.) In both of these passages, in talking of natural selection, Darwin explicitly mentions the transmission of characteristics from one generation to the next. Since, if once it is shown that it is reasonable to hold Natural Selection 2, this third notion of natural selection follows almost as a matter of course (assuming, as Darwin points out, that characteristics can be inherited), I shall not pursue it any further in this paper. 6g Flew, op. cit., note 7, 14. ” That Darwin clearly recognized that not all with favourable variations will survive can be seen in the following passage from the sixth edition of The Origin. ‘It may be well here to remark that with all beings there must be much fortuitous destruction, which can have little or no influence on the course of natural selection. For instance a vast number of eggs or seeds are annually devoured, and these could be modified through natural selection only if they varied in some manner which protected them from their enemies. Yet many of these eggs or seeds would perhaps, if not destroyed, have yielded individuals better adapted to their conditions of life than any of those which happened to survive.’ (I 72 : 6 I. I : f-r 73 : 6 I. 3 : f.)