Volume Ii Part 5 (1/2)
If instinct be, as Professor Hering, Mr. Samuel Butler, and others have argued, ”hereditary habit”--i. e. if it comprises an element of transmitted experience--we at once find a complete explanation of many cases of the display of instinct which otherwise remain inexplicable.
For although a large number--or even, as I believe, a large majority--of instincts are explicable by the theory of natural selection alone, or by supposing that they were gradually developed by the survival of fortuitous variations in the way of advantageous psychological peculiarities, this only applies to comparatively simple instincts, such as that of a protectively coloured animal exhibiting a preference for the surroundings which it resembles, or even adopting att.i.tudes in imitation of objects which occur in such surroundings. But in all cases where instincts become complex and refined, we seem almost compelled to accept Darwin's view that their origin is to be sought in consciously intelligent adjustments on the part of ancestors.
Thus, to give only one example, a species of Sphex preys upon caterpillars, which it stings in their nerve-centres for the purpose of paralyzing, without killing them. The victims, when thus rendered motionless, are then buried with the eggs of the Sphex, in order to serve as food for her larvae which subsequently develop from these eggs.
Now, in order thus to paralyze a caterpillar, the Sphex has to sting it successively in nine minute and particular points along the ventral surface of the animal--and this the Sphex unerringly does, to the exclusion of all other points of the caterpillar's anatomy. Well, such being the facts--according to M. Fabre, who appears to have observed them carefully--it is conceivable enough, as Darwin supposed[48], that the ancestors of the Sphex, being like many other hymenopterous insects highly intelligent, should have observed that on stinging caterpillars in these particular spots a greater amount of effect was produced than could be produced by stinging them anywhere else; and, therefore, that they habitually stung the caterpillars in these places only, till, in course of time, this originally intelligent habit became by heredity instinctive. But now, on the other hand, if we exclude the possibility of this explanation, it appears to me incredible that such an instinct should ever have been evolved at all; for it appears to me incredible that natural selection, unaided by originally intelligent action, could ever have developed such an instinct out of merely fortuitous variations--there being, by hypothesis, nothing to _determine_ variations of an insect's mind in the direction of stinging caterpillars only in these nine intensely localized spots[49].
[48] For details of his explanation of this particular case, for which I particularly inquired, see _Mental Evolution in Animals_, pp. 301-2.
[49] Note B.
Again, there are not a few instincts which appear to be wholly useless to their possessors, and others again which appear to be even deleterious. The dusting over of their excrement by certain freely-roaming carnivora; the choice by certain herbivora of particular places on which to void their urine, or in which to die; the howling of wolves at the moon; purring of cats, &c., under pleasurable emotion; and sundry other hereditary actions of the same apparently unmeaning kind, all admit of being readily accounted for as useless habits originally acquired in various ways, and afterwards perpetuated by heredity, because not sufficiently deleterious to have been stamped out by natural selection[50]. But it does not seem possible to explain them by survival of the fittest in the struggle for existence.
[50] For fuller treatment see _Mental Evolution in Animals_, pp.
274-285, 378-379, 381-383.
Finally, in the case of our own species, it is self-evident that the aesthetic, moral, and religious instincts admit of a natural and easy explanation on the hypothesis of use-inheritance, while such is by no means the case if that hypothesis is rejected. Our emotions of the ludicrous, of the beautiful, and of the sublime, appear to be of the nature of hereditary instincts; and be this as it may, it would further appear that, whatever else they may be, they are certainly not of a life-preserving character. And although this cannot be said of the moral sense when the theory of natural selection is extended from the individual to the tribe, still, when we remember the extraordinary complexity and refinement to which they have attained in civilized man, we may well doubt whether they can have been due to natural selection alone. But s.p.a.ce forbids discussion of this large and important question on the present occasion. Suffice it therefore to say, that I doubt not Weismann himself would be the first to allow that his theory of heredity encounters greater difficulties in the domain of ethics than in any other--unless, indeed, it be that of religion[51].
[51] For an excellent essay on the deleterious character of early forms of religion from a biological point of view, see the Hon.
Lady Welby, _An Apparent Paradox in Mental Evolution_ (Journ.
Anthrop. Inst. May 1891).
I have now given a brief sketch of the indirect evidence in favour of the so-called Lamarckian factors, in so far as this appears fairly deducible from the facts of reflex action and of instinct. It will now be my endeavour to present as briefly what has to be said against this evidence.
As previously observed, the facts of reflex action have not been hitherto adduced in the present connexion. This has led me to occupy considerably more s.p.a.ce in the treatment of them than those of instinct.
On this account, also, there is here nothing to quote, or to consider, _per contra_. On the other hand, however, Weismann has himself dealt with the phenomena of instinct in animals, though not, I think, in man--if we except his brilliant essay on music. Therefore let us now begin this division of our subject by briefly stating, and considering, what he has said upon the subject.
The answer of Weismann to difficulties which arise against the ultra-Darwinian theory in the domain of instinct, is as follows:--
”The necessity for extreme caution in appealing to the supposed hereditary effects of use, is well shown in the case of those numerous instincts which only come into play once in a life-time, and which do not therefore admit of improvement by practice. The queen-bee takes her nuptial flight only once, and yet how many and complex are the instincts and the reflex mechanisms which come into play on that occasion. Again, in many insects the deposition of eggs occurs but once in a life-time, and yet such insects always fulfil the necessary conditions with unfailing accuracy[52].”
[52] _Essays_, i. p. 93.
But in this rejoinder the possibility is forgotten, that although such actions are _now_ performed only once in the individual life-time, _originally_--i.e. when the instincts were being developed in a remote ancestry--they may have been performed on many frequent and successive occasions during the individual life-time. In all the cases quoted by Weismann, instincts of the kind in question bear independent evidence of high antiquity, by occurring in whole genera (or even families), by being a.s.sociated with peculiar and often highly evolved structures required for their performance, and so on. Consequently, in these cases ample time has been allowed for subsequent changes of habit, and of seasonal alterations with respect to propagation--both these things being of frequent and facile occurrence among animals of all kinds, even within periods which fall under actual observation. Nevertheless, I do not question that there are instinctive activities which, as far as we are able to see, can never have been performed more than once in each individual life-time[53]. The fact, however, only goes to show what is fully admitted--that some instincts (and even highly complex instincts) have apparently been developed by natural selection alone. Which, of course, is not equivalent to showing that all instincts must have been developed by natural selection alone. The issue is not to be debated on general grounds like this, but on those of particular cases. Even if it were satisfactorily proved that the instincts of a queen-bee have been developed by natural selection, it would not thereby be proved that such has been the case with the instincts of a Sphex wasp. One can very well understand how the nuptial flight of the former, with all its a.s.sociated actions, may have been brought about by natural selection alone; but this does not help us to understand how the peculiar instincts of the latter can have been thus caused.
[53] See _Mental Evolution in Animals_, pp. 377-8.
Strong evidence in favour of Weismann's views does, however, at first sight seem to be furnished by social hymenoptera in other respects. For not only does the queen present highly specialized and altogether remarkable instincts; but the neuters present totally different and even still more remarkable instincts--which, moreover, are often divided into two or more cla.s.ses, corresponding with the different ”castes.” Yet the neuters, being barren females, never have an opportunity of bequeathing their instincts to progeny. Thus it appears necessary to suppose that the instincts of all the different castes of neuters are latent in the queen and drones, together with the other instincts which are patent in both. Lastly, it seems necessary to suppose that all this wonderful organization of complex and segregated instincts must have been built up by natural selection acting exclusively on the queens and drones--seeing that these exercise their own instincts only once in a life-time, while, as just observed, the neuters cannot possibly bequeath their individual experience to progeny. Obviously, however, natural selection must here be supposed to be operating at an immense disadvantage; for it must have built up the often diverse and always complex instincts of neuters, not directly, but indirectly through the queens and drones, which never manifest any of these instincts themselves.
Now Darwin fully acknowledged the difficulty of attributing these results to the unaided influence of natural selection; but the fact of neuter insects being unable to propagate seemed to him to leave no alternative. And so it seems to Weismann, who accordingly quotes these instincts in support of his views. And so it seemed to me, until my work on _Animal Intelligence_ was translated into French, and an able Preface was supplied to that translation by M. Perrier. In this Preface it is argued that we are not necessarily obliged to exclude the possibility of Lamarckian principles having operated in the original formation of these instincts. On the contrary, if such principles ever operate at all, Perrier shows that here we have a case where it is virtually certain that they must have operated. For although neuter insects are now unable to propagate, their organization indicates--if it does not actually prove--that they are descended from working insects which were able to propagate. Thus, in all probability, what we now call a ”hive” was originally a society of s.e.xually mature insects, all presenting the same instincts, both as to propagation and to co-operation. When these instincts, thus common to all individuals composing the hive, had been highly perfected, it became of advantage in the struggle for existence (between different hives or communities) that the functions of reproduction should devolve more upon some individuals, while those of co-operation should devolve more upon others. Consequently, this division of labour began, and gradually became complete, as we now find it in bees and ants. Perrier sustains the hypothesis thus briefly sketched by pointing to certain species of social hymenoptera where we may actually observe different stages of the process--from cases where all the females of the hive are at the same time workers and breeders, up to the cases where the severance between these functions has become complete. Therefore, it seems to me, it is no longer necessary to suppose that in these latter cases all the instincts of the (now) barren females can only have been due to the unaided influence of natural selection.
Nevertheless, although I think that Perrier has made good his position thus far, that his hypothesis fails to account for some of the instincts which are manifested by neuter insects, such as those which, so far as I can see, must necessarily be supposed to have originated after the breeding and working functions had become separated--seeing that they appear to have exclusive reference to this peculiar state of matters.
Possibly, however, Perrier might be able to meet each of these particular instincts, by showing how they could have arisen out of simpler beginnings, prior to the separation of the two functions in question. There is no s.p.a.ce to consider such possibilities in detail; but, until this shall have been done, I do not think we are ent.i.tled to conclude that the phenomena of instinct as presented by neuter insects are demonstrably incompatible with the doctrines of Lamarck--or, that these phenomena are available as a logical proof of the una.s.sisted agency of natural selection in the case of instincts in general[54].
[54] [See H. Spencer, _The Inadequacy of Natural Selection, A Rejoinder to Professor Weismann_, Contemp. Rev. 1893; and _Weismannism once more_, Ibid. Oct. 1894; Weismann, _The All-sufficiency of Natural Selection_, Ibid. 1893; and _The Effect of External Influences upon Development_, ”Romanes Lecture” 1894: also _Neuter Insects and Lamarckism_, W. Platt Ball, Natural Science, Feb. 1894, and _Neuter Insects and Darwinism_, J. T. Cunningham, Ibid. April 1894. C. Ll. M.]
(B.) _Inherited Effects of Use and of Disuse._
There is no doubt that Darwin everywhere attaches great weight to this line of evidence. Nevertheless, in my opinion, there is equally little doubt that, taken by itself, it is of immeasurably less weight than Darwin supposed. Indeed, I quite agree with Weismann that the whole of this line of evidence is practically worthless; and for the following reasons.