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+ <head>
+ <title>
+ Lecture to Working Men, No. 5 (of 6), The Present Condition of Organic
+ Nature, THE CONDITIONS OF EXISTENCE AS AFFECTING THE PERPETUATION OF
+ LIVING BEINGS by Thomas H. Huxley
+ </title>
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+
+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
+
+Release Date: January 4, 2009 [EBook #2925]
+Last Updated: January 22, 2013
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE CONDITIONS OF EXISTENCE ***
+
+
+
+
+Produced by Amy E. Zelmer, and David Widger
+
+
+
+
+
+
+</pre>
+ <p>
+ <br /><br />
+ </p>
+ <h1>
+ THE CONDITIONS OF EXISTENCE AS <br /> AFFECTING THE PERPETUATION OF LIVING
+ BEINGS
+ </h1>
+ <p>
+ <br />
+ </p>
+ <h3>
+ Lecture V. (of VI.), "Lectures To Working Men", at the Museum of Practical
+ Geology, 1863, On Darwin's work: "Origin of Species".
+ </h3>
+ <p>
+ <br /><br />
+ </p>
+ <h2>
+ By Thomas H. Huxley
+ </h2>
+ <p>
+ <br /> <br />
+ </p>
+ <hr />
+ <p>
+ <br /> <br />
+ </p>
+ <p>
+ 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&mdash;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&mdash;if you took care to breed only from those
+ forms which presented the same peculiarities of any variety which had
+ arisen in this manner&mdash;the variation might be perpetuated, as far as
+ we can see, indefinitely.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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&mdash;that is to say, it is, for the
+ practical naturalist, a mere question of structural differences. <a
+ href="#linknote-1" name="linknoteref-1" id="linknoteref-1"><small>1</small></a>
+ </p>
+ <p>
+ We have seen now&mdash;to repeat this point once more, and it is very
+ essential that we should rightly understand it&mdash;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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ As regards the great majority of physiological characteristics, there is
+ no doubt that they are capable of being developed, increased, and modified
+ by selection.
+ </p>
+ <p>
+ 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,&mdash;as the peculiar habit of
+ tumbling, in the Tumbler&mdash;the peculiarities of flight, in the
+ "homing" birds,&mdash;the strange habit of spreading out the tail, and
+ walking in a peculiar fashion, in the Fantail,&mdash;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.
+ </p>
+ <p>
+ So with Dogs in their habits and instincts. It is a physiological
+ peculiarity which leads the Greyhound to chase its prey by sight,&mdash;that
+ enables the Beagle to track it by the scent,&mdash;that impels the Terrier
+ to its rat-hunting propensity,&mdash;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&mdash;at least about some of
+ them&mdash;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&mdash;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,&mdash;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&mdash;that is, if you couple a male and a female hybrid&mdash;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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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&mdash;so
+ far as we know at present&mdash;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,&mdash;we will say the male and female mongrel,&mdash;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.
+ </p>
+ <p>
+ But while considering this question of the limitations of species, a word
+ must be said about what is called RECURRENCE&mdash;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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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&mdash;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&mdash;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&mdash;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.
+ </p>
+ <p>
+ To sum up,&mdash;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.
+ </p>
+ <p>
+ Now, the next problem that lies before us&mdash;and it is an extremely
+ important one&mdash;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&mdash;and this comes to the same thing&mdash;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&mdash;though it is not direct testimony&mdash;yet it is exceeding
+ good and exceedingly powerful evidence in its way.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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&mdash;they extend to
+ the bony structure, and to the characters of that most important of all
+ organs to us&mdash;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.
+ </p>
+ <p>
+ 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,&mdash;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.
+ </p>
+ <p>
+ 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!
+ </p>
+ <p>
+ 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,&mdash;as
+ spontaneous varieties,&mdash;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.
+ </p>
+ <p>
+ But the question now is:&mdash;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.
+ </p>
+ <p>
+ 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,&mdash;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&mdash;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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ I will suppose, therefore, that all the habitable part of this globe&mdash;the
+ dry land, amounting to about 51,000,000 square miles,&mdash;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:&mdash;
+ </p>
+ <p>
+ <br />
+ </p>
+ <div class="fig" style="width:80%">
+ <img alt="calc (45K)" src="images/calc.jpg" width="100%" /><br />
+ </div>
+ <p>
+ <br />
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ This is a thing which is hardly conceivable&mdash;it seems hardly
+ imaginable&mdash;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,&mdash;and
+ although he was much abused for his conclusions at the time, they have
+ never yet been disproved and never will be&mdash;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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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.
+ </p>
+ <p>
+ 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;&mdash;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,&mdash;that
+ every plant has its indirect helpers in the birds that scatter abroad its
+ seed, and the animals that manure it with their dung;&mdash;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.
+ </p>
+ <p>
+ 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&mdash;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,&mdash;one of the French Cuirassiers, who had on a large
+ blue cloak&mdash;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&mdash;if
+ we may so term it&mdash;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&mdash;the minutest
+ circumstance&mdash;will turn the scale one way or the other.
+ </p>
+ <p>
+ Suppose that by a variation of the black race it had produced the white
+ man at any time&mdash;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&mdash;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.
+ </p>
+ <p>
+ 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&mdash;the
+ cats are therefore the INDIRECT HELPERS of the bees! <a href="#linknote-2"
+ name="linknoteref-2" id="linknoteref-2"><small>2</small></a> 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.
+ </p>
+ <p>
+ <a name="linknote-1" id="linknote-1">
+ <!-- Note --></a>
+ </p>
+ <p class="foot">
+ 1 (<a href="#linknoteref-1">return</a>)<br /> [ 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.]
+ </p>
+ <p>
+ <a name="linknote-2" id="linknote-2">
+ <!-- Note --></a>
+ </p>
+ <p class="foot">
+ 2 (<a href="#linknoteref-2">return</a>)<br /> [ 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.]
+ </p>
+ <p>
+ <br /><br /><br /><br />
+ </p>
+<pre xml:space="preserve">
+
+
+
+
+
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+Affecting The Perpetuation Of Living Beings, by Thomas H. Huxley
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+</pre>
+ </body>
+</html>
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