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diff --git a/2925.txt b/2925.txt new file mode 100644 index 0000000..6335872 --- /dev/null +++ b/2925.txt @@ -0,0 +1,1070 @@ +The Project Gutenberg EBook of The Conditions Of Existence As Affecting +The Perpetuation Of Living Beings, by Thomas H. Huxley + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Conditions Of Existence As Affecting The Perpetuation Of Living Beings + Lecture V. (of V.), Lectures To Working Men, at the Museum + of Practical Geology, 1863, On Darwin's work: "Origin of + Species". + +Author: Thomas H. Huxley + +Posting Date: January 4, 2009 [EBook #2925] +Release Date: November, 2001 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE CONDITIONS OF EXISTENCE *** + + + + +Produced by Amy E. Zelmer + + + + + +THE CONDITIONS OF EXISTENCE AS AFFECTING THE PERPETUATION OF LIVING +BEINGS + +Lecture V. (of VI.), Lectures To Working Men, at the Museum of Practical +Geology, 1863, On Darwin's work: "Origin of Species". + +By Thomas H. Huxley + + + +IN the last Lecture I endeavoured to prove to you that, while, as a +general rule, organic beings tend to reproduce their kind, there is +in them, also, a constantly recurring tendency to vary--to vary to a +greater or to a less extent. Such a variety, I pointed out to you, might +arise from causes which we do not understand; we therefore called it +spontaneous; and it might come into existence as a definite and marked +thing, without any gradations between itself and the form which preceded +it. I further pointed out, that such a variety having once arisen, +might be perpetuated to some extent, and indeed to a very marked extent, +without any direct interference, or without any exercise of that process +which we called selection. And then I stated further, that by such +selection, when exercised artificially--if you took care to breed only +from those forms which presented the same peculiarities of any variety +which had arisen in this manner--the variation might be perpetuated, as +far as we can see, indefinitely. + +The next question, and it is an important one for us, is this: Is there +any limit to the amount of variation from the primitive stock which can +be produced by this process of selective breeding? In considering this +question, it will be useful to class the characteristics, in respect of +which organic beings vary, under two heads: we may consider structural +characteristics, and we may consider physiological characteristics. + +In the first place, as regards structural characteristics, I endeavoured +to show you, by the skeletons which I had upon the table, and by +reference to a great many well-ascertained facts, that the different +breeds of Pigeons, the Carriers, Pouters, and Tumblers, might vary in +any of their internal and important structural characters to a very +great degree; not only might there be changes in the proportions of the +skull, and the characters of the feet and beaks, and so on; but that +there might be an absolute difference in the number of the vertebrae of +the back, as in the sacral vertebrae of the Pouter; and so great is the +extent of the variation in these and similar characters that I pointed +out to you, by reference to the skeletons and the diagrams, that these +extreme varieties may absolutely differ more from one another in their +structural characters than do what naturalists call distinct SPECIES +of pigeons; that is to say, that they differ so much in structure that +there is a greater difference between the Pouter and the Tumbler than +there is between such wild and distinct forms as the Rock Pigeon or +the Ring Pigeon, or the Ring Pigeon and the Stock Dove; and indeed +the differences are of greater value than this, for the structural +differences between these domesticated pigeons are such as would be +admitted by a naturalist, supposing he knew nothing at all about their +origin, to entitle them to constitute even distinct genera. + +As I have used this term SPECIES, and shall probably use it a good deal, +I had better perhaps devote a word or two to explaining what I mean by +it. + +Animals and plants are divided into groups, which become gradually +smaller, beginning with a KINGDOM, which is divided into SUB-KINGDOMS; +then come the smaller divisions called PROVINCES; and so on from a +PROVINCE to a CLASS from a CLASS to an ORDER, from ORDERS to FAMILIES, +and from these to GENERA, until we come at length to the smallest +groups of animals which can be defined one from the other by constant +characters, which are not sexual; and these are what naturalists call +SPECIES in practice, whatever they may do in theory. + +If, in a state of nature, you find any two groups of living beings, +which are separated one from the other by some constantly-recurring +characteristic, I don't care how slight and trivial, so long as it is +defined and constant, and does not depend on sexual peculiarities, then +all naturalists agree in calling them two species; that is what is meant +by the use of the word species--that is to say, it is, for the practical +naturalist, a mere question of structural differences. [1] + +We have seen now--to repeat this point once more, and it is very +essential that we should rightly understand it--we have seen that +breeds, known to have been derived from a common stock by selection, may +be as different in their structure from the original stock as species +may be distinct from each other. + +But is the like true of the physiological characteristics of animals? +Do the physiological differences of varieties amount in degree to those +observed between forms which naturalists call distinct species? This is +a most important point for us to consider. + +As regards the great majority of physiological characteristics, there +is no doubt that they are capable of being developed, increased, and +modified by selection. + +There is no doubt that breeds may be made as different as species in +many physiological characters. I have already pointed out to you very +briefly the different habits of the breeds of Pigeons, all of which +depend upon their physiological peculiarities,--as the peculiar habit of +tumbling, in the Tumbler--the peculiarities of flight, in the "homing" +birds,--the strange habit of spreading out the tail, and walking in a +peculiar fashion, in the Fantail,--and, lastly, the habit of blowing +out the gullet, so characteristic of the Pouter. These are all due +to physiological modifications, and in all these respects these birds +differ as much from each other as any two ordinary species do. + +So with Dogs in their habits and instincts. It is a physiological +peculiarity which leads the Greyhound to chase its prey by sight,--that +enables the Beagle to track it by the scent,--that impels the Terrier to +its rat-hunting propensity,--and that leads the Retriever to its +habit of retrieving. These habits and instincts are all the results of +physiological differences and peculiarities, which have been developed +from a common stock, at least there is every reason to believe so. +But it is a most singular circumstance, that while you may run through +almost the whole series of physiological processes, without finding a +check to your argument, you come at last to a point where you do find +a check, and that is in the reproductive processes. For there is a most +singular circumstance in respect to natural species--at least about some +of them--and it would be sufficient for the purposes of this argument if +it were true of only one of them, but there is, in fact, a great number +of such cases--and that is, that, similar as they may appear to be +to mere races or breeds, they present a marked peculiarity in the +reproductive process. If you breed from the male and female of the same +race, you of course have offspring of the like kind, and if you make the +offspring breed together, you obtain the same result, and if you breed +from these again, you will still have the same kind of offspring; there +is no check. But if you take members of two distinct species, however +similar they may be to each other and make them breed together, you will +find a check, with some modifications and exceptions, however, which I +shall speak of presently. If you cross two such species with each other, +then,--although you may get offspring in the case of the first cross, +yet, if you attempt to breed from the products of that crossing, which +are what are called HYBRIDS--that is, if you couple a male and a female +hybrid--then the result is that in ninety-nine cases out of a hundred +you will get no offspring at all; there will be no result whatsoever. + +The reason of this is quite obvious in some cases; the male hybrids, +although possessing all the external appearances and characteristics +of perfect animals, are physiologically imperfect and deficient in the +structural parts of the reproductive elements necessary to generation. +It is said to be invariably the case with the male mule, the cross +between the Ass and the Mare; and hence it is, that, although crossing +the Horse with the Ass is easy enough, and is constantly done, as far as +I am aware, if you take two mules, a male and a female, and endeavour to +breed from them, you get no offspring whatever; no generation will take +place. This is what is called the sterility of the hybrids between two +distinct species. + +You see that this is a very extraordinary circumstance; one does not see +why it should be. The common teleological explanation is, that it is +to prevent the impurity of the blood resulting from the crossing of one +species with another, but you see it does not in reality do anything of +the kind. There is nothing in this fact that hybrids cannot breed with +each other, to establish such a theory; there is nothing to prevent the +Horse breeding with the Ass, or the Ass with the Horse. So that this +explanation breaks down, as a great many explanations of this kind do, +that are only founded on mere assumptions. + +Thus you see that there is a great difference between "mongrels," which +are crosses between distinct races, and "hybrids," which are crosses +between distinct species. The mongrels are, so far as we know, fertile +with one another. But between species, in many cases, you cannot succeed +in obtaining even the first cross: at any rate it is quite certain that +the hybrids are often absolutely infertile one with another. + +Here is a feature, then, great or small as it may be, which +distinguishes natural species of animals. Can we find any approximation +to this in the different races known to be produced by selective +breeding from a common stock? Up to the present time the answer to that +question is absolutely a negative one. As far as we know at present, +there is nothing approximating to this check. In crossing the breeds +between the Fantail and the Pouter, the Carrier and the Tumbler, or any +other variety or race you may name--so far as we know at present--there +is no difficulty in breeding together the mongrels. Take the Carrier and +the Fantail, for instance, and let them represent the Horse and the Ass +in the case of distinct species; then you have, as the result of their +breeding, the Carrier-Fantail mongrel,--we will say the male and female +mongrel,--and, as far as we know, these two when crossed would not be +less fertile than the original cross, or than Carrier with Carrier. +Here, you see, is a physiological contrast between the races produced +by selective modification and natural species. I shall inquire into the +value of this fact, and of some modifying circumstances by and by; for +the present I merely put it broadly before you. + +But while considering this question of the limitations of species, a +word must be said about what is called RECURRENCE--the tendency of races +which have been developed by selective breeding from varieties to return +to their primitive type. This is supposed by many to put an absolute +limit to the extent of selective and all other variations. People say, +"It is all very well to talk about producing these different races, +but you know very well that if you turned all these birds wild, these +Pouters, and Carriers, and so on, they would all return to their +primitive stock." This is very commonly assumed to be a fact, and it is +an argument that is commonly brought forward as conclusive; but if you +will take the trouble to inquire into it rather closely, I think you +will find that it is not worth very much. The first question of course +is, Do they thus return to the primitive stock? And commonly as the +thing is assumed and accepted, it is extremely difficult to get anything +like good evidence of it. It is constantly said, for example, that if +domesticated Horses are turned wild, as they have been in some parts of +Asia Minor and South America, that they return at once to the primitive +stock from which they were bred. But the first answer that you make to +this assumption is, to ask who knows what the primitive stock was; and +the second answer is, that in that case the wild Horses of Asia Minor +ought to be exactly like the wild Horses of South America. If they are +both like the same thing, they ought manifestly to be like each other! +The best authorities, however, tell you that it is quite different. The +wild Horse of Asia is said to be of a dun colour, with a largish head, +and a great many other peculiarities; while the best authorities on +the wild Horses of South America tell you that there is no similarity +between their wild Horses and those of Asia Minor; the cut of their +heads is very different, and they are commonly chestnut or bay-coloured. +It is quite clear, therefore, that as by these facts there ought to +have been two primitive stocks, they go for nothing in support of the +assumption that races recur to one primitive stock, and so far as this +evidence is concerned, it falls to the ground. + +Suppose for a moment that it were so, and that domesticated races, when +turned wild, did return to some common condition, I cannot see that this +would prove much more than that similar conditions are likely to produce +similar results; and that when you take back domesticated animals into +what we call natural conditions, you do exactly the same thing as if you +carefully undid all the work you had gone through, for the purpose of +bringing the animal from its wild to its domesticated state. I do not +see anything very wonderful in the fact, if it took all that trouble to +get it from a wild state, that it should go back into its original state +as soon as you removed the conditions which produced the variation to +the domesticated form. There is an important fact, however, forcibly +brought forward by Mr. Darwin, which has been noticed in connection with +the breeding of domesticated pigeons; and it is, that however different +these breeds of pigeons may be from each other, and we have already +noticed the great differences in these breeds, that if, among any of +those variations, you chance to have a blue pigeon turn up, it will be +sure to have the black bars across the wings, which are characteristic +of the original wild stock, the Rock Pigeon. + +Now, this is certainly a very remarkable circumstance; but I do not see +myself how it tells very strongly either one way or the other. I think, +in fact, that this argument in favour of recurrence to the primitive +type might prove a great deal too much for those who so constantly +bring it forward. For example, Mr. Darwin has very forcibly urged, +that nothing is commoner than if you examine a dun horse--and I had an +opportunity of verifying this illustration lately, while in the islands +of the West Highlands, where there are a great many dun horses--to find +that horse exhibit a long black stripe down his back, very often stripes +on his shoulder, and very often stripes on his legs. I, myself, saw +a pony of this description a short time ago, in a baker's cart, near +Rothesay, in Bute: it had the long stripe down the back, and stripes on +the shoulders and legs, just like those of the Ass, the Quagga, and the +Zebra. Now, if we interpret the theory of recurrence as applied to +this case, might it not be said that here was a case of a variation +exhibiting the characters and conditions of an animal occupying +something like an intermediate position between the Horse, the Ass, the +Quagga, and the Zebra, and from which these had been developed? In the +same way with regard even to Man. Every anatomist will tell you that +there is nothing commoner, in dissecting the human body, than to meet +with what are called muscular variations--that is, if you dissect +two bodies very carefully, you will probably find that the modes of +attachment and insertion of the muscles are not exactly the same in +both, there being great peculiarities in the mode in which the muscles +are arranged; and it is very singular, that in some dissections of the +human body you will come upon arrangements of the muscles very similar +indeed to the same parts in the Apes. Is the conclusion in that case to +be, that this is like the black bars in the case of the Pigeon, and that +it indicates a recurrence to the primitive type from which the animals +have been probably developed? Truly, I think that the opponents of +modification and variation had better leave the argument of recurrence +alone, or it may prove altogether too strong for them. + +To sum up,--the evidence as far as we have gone is against the argument +as to any limit to divergences, so far as structure is concerned; and +in favour of a physiological limitation. By selective breeding we can +produce structural divergences as great as those of species, but we +cannot produce equal physiological divergences. For the present I leave +the question there. + +Now, the next problem that lies before us--and it is an extremely +important one--is this: Does this selective breeding occur in nature? +Because, if there is no proof of it, all that I have been telling you +goes for nothing in accounting for the origin of species. Are natural +causes competent to play the part of selection in perpetuating +varieties? Here we labour under very great difficulties. In the last +lecture I had occasion to point out to you the extreme difficulty of +obtaining evidence even of the first origin of those varieties which we +know to have occurred in domesticated animals. I told you, that almost +always the origin of these varieties is overlooked, so that I could only +produce two of three cases, as that of Gratio Kelleia and of the Ancon +sheep. People forget, or do not take notice of them until they come to +have a prominence; and if that is true of artificial cases, under our +own eyes, and in animals in our own care, how much more difficult it +must be to have at first hand good evidence of the origin of varieties +in nature! Indeed, I do not know that it is possible by direct evidence +to prove the origin of a variety in nature, or to prove selective +breeding; but I will tell you what we can prove--and this comes to the +same thing--that varieties exist in nature within the limits of species, +and, what is more, that when a variety has come into existence in +nature, there are natural causes and conditions, which are amply +competent to play the part of a selective breeder; and although that +is not quite the evidence that one would like to have--though it is +not direct testimony--yet it is exceeding good and exceedingly powerful +evidence in its way. + +As to the first point, of varieties existing among natural species, I +might appeal to the universal experience of every naturalist, and of any +person who has ever turned any attention at all to the characteristics +of plants and animals in a state of nature; but I may as well take a few +definite cases, and I will begin with Man himself. + +I am one of those who believe that, at present, there is no evidence +whatever for saying, that mankind sprang originally from any more than a +single pair; I must say, that I cannot see any good ground whatever, or +even any tenable sort of evidence, for believing that there is more than +one species of Man. Nevertheless, as you know, just as there are numbers +of varieties in animals, so there are remarkable varieties of men. I +speak not merely of those broad and distinct variations which you see at +a glance. Everybody, of course, knows the difference between a Negro and +a white man, and can tell a Chinaman from an Englishman. They each +have peculiar characteristics of colour and physiognomy; but you must +recollect that the characters of these races go very far deeper--they +extend to the bony structure, and to the characters of that most +important of all organs to us--the brain; so that, among men belonging +to different races, or even within the same race, one man shall have a +brain a third, or half, or even seventy per cent. bigger than another; +and if you take the whole range of human brains, you will find a +variation in some cases of a hundred per cent. Apart from these +variations in the size of the brain, the characters of the skull vary. +Thus if I draw the figures of a Mongul and of a Negro head on the +blackboard, in the case of the last the breadth would be about +seven-tenths, and in the other it would be nine-tenths of the total +length. So that you see there is abundant evidence of variation among +men in their natural condition. And if you turn to other animals there +is just the same thing. The fox, for example, which has a very large +geographical distribution all over Europe, and parts of Asia, and on the +American Continent, varies greatly. There are mostly large foxes in the +North, and smaller ones in the South. In Germany alone, the foresters +reckon some eight different sorts. + +Of the tiger, no one supposes that there is more than one species; they +extend from the hottest parts of Bengal, into the dry, cold, bitter +steppes of Siberia, into a latitude of 50 degrees,--so that they may +even prey upon the reindeer. These tigers have exceedingly different +characteristics, but still they all keep their general features, so that +there is no doubt as to their being tigers. The Siberian tiger has a +thick fur, a small mane, and a longitudinal stripe down the back, while +the tigers of Java and Sumatra differ in many important respects from +the tigers of Northern Asia. So lions vary; so birds vary; and so, if +you go further back and lower down in creation, you find that fishes +vary. In different streams, in the same country even, you will find the +trout to be quite different to each other and easily recognisable by +those who fish in the particular streams. There is the same differences +in leeches; leech collectors can easily point out to you the differences +and the peculiarities which you yourself would probably pass by; so with +fresh-water mussels; so, in fact, with every animal you can mention. + +In plants there is the same kind of variation. Take such a case even as +the common bramble. The botanists are all at war about it; some of +them wanting to make out that there are many species of it, and others +maintaining that they are but many varieties of one species; and they +cannot settle to this day which is a species and which is a variety! + +So that there can be no doubt whatsoever that any plant and any +animal may vary in nature; that varieties may arise in the way I have +described,--as spontaneous varieties,--and that those varieties may be +perpetuated in the same way that I have shown you spontaneous varieties +are perpetuated; I say, therefore, that there can be no doubt as to the +origin and perpetuation of varieties in nature. + +But the question now is:--Does selection take place in nature? is there +anything like the operation of man in exercising selective breeding, +taking place in nature? You will observe that, at present, I say nothing +about species; I wish to confine myself to the consideration of the +production of those natural races which everybody admits to exist. The +question is, whether in nature there are causes competent to produce +races, just in the same way as man is able to produce by selection, such +races of animals as we have already noticed. + +When a variety has arisen, the CONDITIONS OF EXISTENCE are such as to +exercise an influence which is exactly comparable to that of artificial +selection. By Conditions of Existence I mean two things,--there are +conditions which are furnished by the physical, the inorganic world, +and there are conditions of existence which are furnished by the organic +world. There is, in the first place, CLIMATE; under that head I include +only temperature and the varied amount of moisture of particular places. +In the next place there is what is technically called STATION, which +means--given the climate, the particular kind of place in which an +animal or a plant lives or grows; for example, the station of a fish +is in the water, of a fresh-water fish in fresh water; the station of a +marine fish is in the sea, and a marine animal may have a station higher +or deeper. So again with land animals: the differences in their stations +are those of different soils and neighbourhoods; some being best adapted +to a calcareous, and others to an arenaceous soil. The third condition +of existence is FOOD, by which I mean food in the broadest sense, the +supply of the materials necessary to the existence of an organic being; +in the case of a plant the inorganic matters, such as carbonic acid, +water, ammonia, and the earthy salts or salines; in the case of the +animal the inorganic and organic matters, which we have seen they +require; then these are all, at least the two first, what we may +call the inorganic or physical conditions of existence. Food takes a +mid-place, and then come the organic conditions; by which I mean the +conditions which depend upon the state of the rest of the organic +creation, upon the number and kind of living beings, with which an +animal is surrounded. You may class these under two heads: there are +organic beings, which operate as 'opponents', and there are organic +beings which operate as 'helpers' to any given organic creature. The +opponents may be of two kinds: there are the 'indirect opponents', which +are what we may call 'rivals'; and there are the 'direct opponents', +those which strive to destroy the creature; and these we call 'enemies'. +By rivals I mean, of course, in the case of plants, those which require +for their support the same kind of soil and station, and, among animals, +those which require the same kind of station, or food, or climate; those +are the indirect opponents; the direct opponents are, of course, those +which prey upon an animal or vegetable. The 'helpers' may also be +regarded as direct and indirect: in the case of a carnivorous animal, +for example, a particular herbaceous plant may in multiplying be an +indirect helper, by enabling the herbivora on which the carnivore preys +to get more food, and thus to nourish the carnivore more abundantly; +the direct helper may be best illustrated by reference to some parasitic +creature, such as the tape-worm. The tape-worm exists in the human +intestines, so that the fewer there are of men the fewer there will be +of tape-worms, other things being alike. It is a humiliating reflection, +perhaps, that we may be classed as direct helpers to the tape-worm, but +the fact is so: we can all see that if there were no men there would be +no tape-worms. + +It is extremely difficult to estimate, in a proper way, the importance +and the working of the Conditions of Existence. I do not think there +were any of us who had the remotest notion of properly estimating them +until the publication of Mr. Darwin's work, which has placed them before +us with remarkable clearness; and I must endeavour, as far as I can in +my own fashion, to give you some notion of how they work. We shall find +it easiest to take a simple case, and one as free as possible from every +kind of complication. + +I will suppose, therefore, that all the habitable part of this +globe--the dry land, amounting to about 51,000,000 square miles,--I will +suppose that the whole of that dry land has the same climate, and that +it is composed of the same kind of rock or soil, so that there will be +the same station everywhere; we thus get rid of the peculiar influence +of different climates and stations. I will then imagine that there shall +be but one organic being in the world, and that shall be a plant. In +this we start fair. Its food is to be carbonic acid, water and ammonia, +and the saline matters in the soil, which are, by the supposition, +everywhere alike. We take one single plant, with no opponents, no +helpers, and no rivals; it is to be a "fair field, and no favour". Now, +I will ask you to imagine further that it shall be a plant which shall +produce every year fifty seeds, which is a very moderate number for a +plant to produce; and that, by the action of the winds and currents, +these seeds shall be equally and gradually distributed over the whole +surface of the land. I want you now to trace out what will occur, and +you will observe that I am not talking fallaciously any more than a +mathematician does when he expounds his problem. If you show that the +conditions of your problem are such as may actually occur in nature and +do not transgress any of the known laws of nature in working out your +proposition, then you are as safe in the conclusion you arrive at as +is the mathematician in arriving at the solution of his problem. In +science, the only way of getting rid of the complications with which a +subject of this kind is environed, is to work in this deductive method. +What will be the result, then? I will suppose that every plant requires +one square foot of ground to live upon; and the result will be that, +in the course of nine years, the plant will have occupied every single +available spot in the whole globe! I have chalked upon the blackboard +the figures by which I arrive at the result:-- + +Plants. + Plants 1 x 50 in 1st year = 50 + 50 x 50 " 2nd " = 2,500 2,500 x +50 " 3rd " = 125,000 125,000 x 50 " 4th " = 6,250,000 6,250,000 x 50 +" 5th " = 312,500,000 312,500,000 x 50 " 6th " = 15,625,000,000 +15,625,000,000 x 50 " 7th " = 781,250,000,000 781,250,000,000 x 50 " +8th " = 39,062,500,000,000 39,062,500,000,000 x 50& " 9th " = +1,953,125,000,000,000 + +51,000,000 sq. miles--the dry surface of the earth x 27,878,400--the +number of sq. ft. in 1 sq. mile = sq. ft. 1,421,798,400,000,000 being +531,326,600,000,000 square feet less than would be required at the end +of the ninth year. + +You will see from this that, at the end of the first year the single +plant will have produced fifty more of its kind; by the end of the +second year these will have increased to 2,500; and so on, in succeeding +years, you get beyond even trillions; and I am not at all sure that I +could tell you what the proper arithmetical denomination of the total +number really is; but, at any rate, you will understand the meaning of +all those noughts. Then you see that, at the bottom, I have taken the +51,000,000 of square miles, constituting the surface of the dry land; +and as the number of square feet are placed under and subtracted from +the number of seeds that would be produced in the ninth year, you can +see at once that there would be an immense number more of plants than +there would be square feet of ground for their accommodation. This is +certainly quite enough to prove my point; that between the eighth and +ninth year after being planted the single plant would have stocked the +whole available surface of the earth. + +This is a thing which is hardly conceivable--it seems hardly +imaginable--yet it is so. It is indeed simply the law of Malthus +exemplified. Mr. Malthus was a clergyman, who worked out this +subject most minutely and truthfully some years ago; he showed quite +clearly,--and although he was much abused for his conclusions at the +time, they have never yet been disproved and never will be--he showed +that in consequence of the increase in the number of organic beings in +a geometrical ratio, while the means of existence cannot be made to +increase in the same ratio, that there must come a time when the number +of organic beings will be in excess of the power of production of +nutriment, and that thus some check must arise to the further increase +of those organic beings. At the end of the ninth year we have seen that +each plant would not be able to get its full square foot of ground, and +at the end of another year it would have to share that space with fifty +others the produce of the seeds which it would give off. + +What, then, takes place? Every plant grows up, flourishes, occupies its +square foot of ground, and gives off its fifty seeds; but notice this, +that out of this number only one can come to anything; there is thus, +as it were, forty-nine chances to one against its growing up; it depends +upon the most fortuitous circumstances whether any one of these fifty +seeds shall grow up and flourish, or whether it shall die and perish. +This is what Mr. Darwin has drawn attention to, and called the "STRUGGLE +FOR EXISTENCE"; and I have taken this simple case of a plant because +some people imagine that the phrase seems to imply a sort of fight. + +I have taken this plant and shown you that this is the result of the +ratio of the increase, the necessary result of the arrival of a time +coming for every species when exactly as many members must be destroyed +as are born; that is the inevitable ultimate result of the rate of +production. Now, what is the result of all this? I have said that there +are forty-nine struggling against every one; and it amounts to this, +that the smallest possible start given to any one seed may give it an +advantage which will enable it to get ahead of all the others; anything +that will enable any one of these seeds to germinate six hours before +any of the others will, other things being alike, enable it to choke +them out altogether. I have shown you that there is no particular in +which plants will not vary from each other; it is quite possible +that one of our imaginary plants may vary in such a character as the +thickness of the integument of its seeds; it might happen that one of +the plants might produce seeds having a thinner integument, and that +would enable the seeds of that plant to germinate a little quicker +than those of any of the others, and those seeds would most inevitably +extinguish the forty-nine times as many that were struggling with them. + +I have put it in this way, but you see the practical result of the +process is the same as if some person had nurtured the one and destroyed +the other seeds. It does not matter how the variation is produced, so +long as it is once allowed to occur. The variation in the plant once +fairly started tends to become hereditary and reproduce itself; the +seeds would spread themselves in the same way and take part in the +struggle with the forty-nine hundred, or forty-nine thousand, with which +they might be exposed. Thus, by degrees, this variety, with some slight +organic change or modification, must spread itself over the whole +surface of the habitable globe, and extirpate or replace the other +kinds. That is what is meant by NATURAL SELECTION; that is the kind of +argument by which it is perfectly demonstrable that the conditions of +existence may play exactly the same part for natural varieties as man +does for domesticated varieties. No one doubts at all that particular +circumstances may be more favourable for one plant and less so for +another, and the moment you admit that, you admit the selective power of +nature. Now, although I have been putting a hypothetical case, you must +not suppose that I have been reasoning hypothetically. There are plenty +of direct experiments which bear out what we may call the theory of +natural selection; there is extremely good authority for the statement +that if you take the seed of mixed varieties of wheat and sow it, +collecting the seed next year and sowing it again, at length you will +find that out of all your varieties only two or three have lived, or +perhaps even only one. There were one or two varieties which were best +fitted to get on, and they have killed out the other kinds in just +the same way and with just the same certainty as if you had taken the +trouble to remove them. As I have already said, the operation of nature +is exactly the same as the artificial operation of man. + +But if this be true of that simple case, which I put before you, where +there is nothing but the rivalry of one member of a species with others, +what must be the operation of selective conditions, when you recollect +as a matter of fact, that for every species of animal or plant there +are fifty or a hundred species which might all, more or less, be +comprehended in the same climate, food, and station;--that every plant +has multitudinous animals which prey upon it, and which are its direct +opponents; and that these have other animals preying upon them,--that +every plant has its indirect helpers in the birds that scatter abroad +its seed, and the animals that manure it with their dung;--I say, when +these things are considered, it seems impossible that any variation +which may arise in a species in nature should not tend in some way or +other either to be a little better or worse than the previous stock; +if it is a little better it will have an advantage over and tend to +extirpate the latter in this crush and struggle; and if it is a little +worse it will itself be extirpated. + +I know nothing that more appropriately expresses this, than the phrase, +"the struggle for existence"; because it brings before your minds, in a +vivid sort of way, some of the simplest possible circumstances connected +with it. When a struggle is intense there must be some who are sure to +be trodden down, crushed, and overpowered by others; and there will be +some who just manage to get through only by the help of the slightest +accident. I recollect reading an account of the famous retreat of +the French troops, under Napoleon, from Moscow. Worn out, tired, and +dejected, they at length came to a great river over which there was +but one bridge for the passage of the vast army. Disorganised and +demoralised as that army was, the struggle must certainly have been a +terrible one--every one heeding only himself, and crushing through the +ranks and treading down his fellows. The writer of the narrative, who +was himself one of those who were fortunate enough to succeed in getting +over, and not among the thousands who were left behind or forced into +the river, ascribed his escape to the fact that he saw striding onward +through the mass a great strong fellow,--one of the French Cuirassiers, +who had on a large blue cloak--and he had enough presence of mind to +catch and retain a hold of this strong man's cloak. He says, "I caught +hold of his cloak, and although he swore at me and cut at and struck me +by turns, and at last, when he found he could not shake me off, fell to +entreating me to leave go or I should prevent him from escaping, besides +not assisting myself, I still kept tight hold of him, and would not quit +my grasp until he had at last dragged me through." Here you see was +a case of selective saving--if we may so term it--depending for its +success on the strength of the cloth of the Cuirassier's cloak. It is +the same in nature; every species has its bridge of Beresina; it has +to fight its way through and struggle with other species; and when well +nigh overpowered, it may be that the smallest chance, something in its +colour, perhaps--the minutest circumstance--will turn the scale one way +or the other. + +Suppose that by a variation of the black race it had produced the white +man at any time--you know that the Negroes are said to believe this to +have been the case, and to imagine that Cain was the first white man, +and that we are his descendants--suppose that this had ever happened, +and that the first residence of this human being was on the West Coast +of Africa. There is no great structural difference between the white man +and the Negro, and yet there is something so singularly different in the +constitution of the two, that the malarias of that country, which do not +hurt the black at all, cut off and destroy the white. Then you see there +would have been a selective operation performed; if the white man had +risen in that way, he would have been selected out and removed by means +of the malaria. Now there really is a very curious case of selection of +this sort among pigs, and it is a case of selection of colour too. +In the woods of Florida there are a great many pigs, and it is a very +curious thing that they are all black, every one of them. Professor +Wyman was there some years ago, and on noticing no pigs but these black +ones, he asked some of the people how it was that they had no white +pigs, and the reply was that in the woods of Florida there was a root +which they called the Paint Root, and that if the white pigs were to eat +any of it, it had the effect of making their hoofs crack, and they died, +but if the black pigs eat any of it, it did not hurt them at all. Here +was a very simple case of natural selection. A skilful breeder could not +more carefully develope the black breed of pigs, and weed out all the +white pigs, than the Paint Root does. + +To show you how remarkably indirect may be such natural selective +agencies as I have referred to, I will conclude by noticing a case +mentioned by Mr. Darwin, and which is certainly one of the most curious +of its kind. It is that of the Humble Bee. It has been noticed that +there are a great many more humble bees in the neighbourhood of towns, +than out in the open country; and the explanation of the matter is this: +the humble bees build nests, in which they store their honey and deposit +the larvae and eggs. The field mice are amazingly fond of the honey and +larvae; therefore, wherever there are plenty of field mice, as in the +country, the humble bees are kept down; but in the neighbourhood of +towns, the number of cats which prowl about the fields eat up the field +mice, and of course the more mice they eat up the less there are to prey +upon the larvae of the bees--the cats are therefore the INDIRECT HELPERS +of the bees! [2] Coming back a step farther we may say that the old +maids are also indirect friends of the humble bees, and indirect enemies +of the field mice, as they keep the cats which eat up the latter! This +is an illustration somewhat beneath the dignity of the subject, perhaps, +but it occurs to me in passing, and with it I will conclude this +lecture. + + + +[Footnote 1: I lay stress here on the 'practical' signification of +"Species." Whether a physiological test between species exist or not, it +is hardly ever applicable by the practical naturalist.] + + +[Footnote 2: The humble bees, on the other hand, are direct helpers of +some plants, such as the heartsease and red clover, which are fertilized +by the visits of the bees; and they are indirect helpers of the numerous +insects which are more or less completely supported by the heartsease +and red clover.] + + + + + +End of the Project Gutenberg EBook of The Conditions Of Existence As +Affecting The Perpetuation Of Living Beings, by Thomas H. Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK THE CONDITIONS OF EXISTENCE *** + +***** This file should be named 2925.txt or 2925.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/9/2/2925/ + +Produced by Amy E. 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