Secondly, there is a variation, to a certain extent--though, in all

probability, the influence of this cause has been very much

exaggerated--but there is no doubt that variation is produced, to a certain

extent, by what are commonly known as external conditions,--such as

temperature, food, warmth, and moisture. In the long run, every variation

depends, in some sense, upon external conditions, seeing that everything

has a cause of its own. I use the term "external conditions" now in the

sense in which it is ordinarily employed: certain it is, that external

conditions have a definite effect. You may take a plant which has single

flowers, and by dealing with the soil, and nourishment, and so on, you may

by and by convert single flowers into double flowers, and make thorns shoot

out into branches. You may thicken or make various modifications in the

shape of the fruit. In animals, too, you may produce analogous changes in

this way, as in the case of that deep bronze colour which persons rarely

lose after having passed any length of time in tropical countries. You may

also alter the development of the muscles very much, by dint of training;

all the world knows that exercise has a great effect in this way; we always

expect to find the arm of a blacksmith hard and wiry, and possessing a

large development of the brachial muscles. No doubt training, which is one

of the forms of external conditions, converts what are originally only

instructions, teachings, into habits, or, in other words, into

organisations, to a great extent; but this second cause of variation cannot

be considered to be by any means a large one. The third cause that I have

to mention, however, is a very extensive one. It is one that, for want of a

better name, has been called "spontaneous variation"; which means that when

we do not know anything about the cause of phenomena, we call it

spontaneous. In the orderly chain of causes and effects in this world,

there are very few things of which it can be said with truth that they are

spontaneous. Certainly not in these physical matters--in these there is

nothing of the kind--everything depends on previous conditions. But when we

cannot trace the cause of phenomena, we call them spontaneous.

Of these variations, multitudinous as they are, but little is known with

perfect accuracy. I will mention to you some two or three cases, because

they are very remarkable in themselves, and also because I shall want to

use them afterwards. Réaumur, a famous French naturalist, a great many

years ago, in an essay which he wrote upon the art of hatching

chickens--which was indeed a very curious essay--had occasion to speak of

variations and monstrosities. One very remarkable case had come under his

notice of a variation in the form of a human member, in the person of a

Maltese, of the name of Gratio Kelleia, who was born with six fingers upon

each hand, and the like number of toes to each of his feet. That was a case

of spontaneous variation. Nobody knows why he was born with that number of

fingers and toes, and as we don't know, we call it a case of "spontaneous"

variation. There is another remarkable case also. I select these, because

they happen to have been observed and noted very carefully at the time. It

frequently happens that a variation occurs, but the persons who notice it

do not take any care in noting down the particulars, until at length, when

inquiries come to be made, the exact circumstances are forgotten; and

hence, multitudinous as may be such "spontaneous" variations, it is

exceedingly difficult to get at the origin of them.

The second case is one of which you may find the whole details in the

"Philosophical Transactions" for the year 1813, in a paper communicated by

Colonel Humphrey to the President of the Royal Society--"On a new Variety

in the Breed of Sheep," giving an account of a very remarkable breed of

sheep, which at one time was well known in the northern states of America,

and which went by the name of the Ancon or the Otter breed of sheep. In the

year 1791, there was a farmer of the name of Seth Wright in Massachusetts,

who had a flock of sheep, consisting of a ram and, I think, of some twelve

or thirteen ewes. Of this flock of ewes, one at the breeding-time bore a

lamb which was very singularly formed; it had a very long body, very short

legs, and those legs were bowed. I will tell you by and by how this

singular variation in the breed of sheep came to be noted, and to have the

prominence that it now has. For the present, I mention only these two

cases; but the extent of variation in the breed of animals is perfectly

obvious to any one who has studied natural history with ordinary attention,

or to any person who compares animals with others of the same kind. It is

strictly true that there are never any two specimens which are exactly

alike; however similar, they will always differ in some certain particular.

Now let us go back to Atavism--to the hereditary tendency I spoke of. What

will come of a variation when you breed from it, when Atavism comes, if I

may say so, to intersect variation? The two cases of which I have mentioned

the history give a most excellent illustration of what occurs. Gratio

Kelleia, the Maltese, married when he was twenty-two years of age, and, as

I suppose there were no six-fingered ladies in Malta, he married an

ordinary five-fingered person. The result of that marriage was four

children; the first, who was christened Salvator, had six fingers and six

toes, like his father; the second was George, who had five fingers and

toes, but one of them was deformed, showing a tendency to variation; the

third was Andrè; he had five fingers and five toes, quite perfect; the

fourth was a girl, Marie; she had five fingers and five toes, but her

thumbs were deformed, showing a tendency toward the sixth.

These children grew up, and when they came to adult years, they all

married, and of course it happened that they all married five-fingered and

five-toed persons. Now let us see what were the results. Salvator had four

children; they were two boys, a girl, and another boy; the first two boys

and the girl were six-fingered and six-toed like their grandfather; the

fourth boy had only five fingers and five toes. George had only four

children; there were two girls with six fingers and six toes; there was one

girl with six fingers and five toes on the right side, and five fingers and

five toes on the left side, so that she was half and half. The last, a boy,

had five fingers and five toes. The third, Andrè, you will recollect, was

perfectly well-formed, and he had many children whose hands and feet were

all regularly developed. Marie, the last, who, of course, married a man who

had only five fingers, had four children; the first, a boy, was born with

six toes, but the other three were normal.

Now observe what very extraordinary phenomena are presented here. You have

an accidental variation giving rise to what you may call a monstrosity; you

have that monstrosity or variation diluted in the first instance by an

admixture with a female of normal construction, and you would naturally

expect that, in the results of such an union, the monstrosity, if repeated,

would be in equal proportion with the normal type; that is to say, that the

children would be half and half, some taking the peculiarity of the father,

and the others being of the purely normal type of the mother; but you see

we have a great preponderance of the abnormal type. Well, this comes to be

mixed once more with the pure, the normal type, and the abnormal is again

produced in large proportion, notwithstanding the second dilution. Now what

would have happened if these abnormal types had intermarried with each

other; that is to say, suppose the two boys of Salvator had taken it into

their heads to marry their first cousins, the two first girls of George,

their uncle? You will remember that these are all of the abnormal type of

their grandfather. The result would probably have been, that their

offspring would have been in every case a further development of that

abnormal type. You see it is only in the fourth, in the person of Marie,

that the tendency, when it appears but slightly in the second generation,

is washed out in the third, while the progeny of Andrè, who escaped in the

first instance, escape altogether.

We have in this case a good example of nature's tendency to the

perpetuation of a variation. Here it is certainly a variation which earned

with it no use or benefit; and yet you see the tendency to perpetuation may

be so strong, that, notwithstanding a great admixture of pure blood, the

variety continues itself up to the third generation, which is largely

marked with it. In this case, as I have said, there was no means of the

second generation intermarrying with any but five-fingered persons, and the

question naturally suggests itself, What would have been the result of such

marriage? Réaumur narrates this case only as far as the third generation.

Certainly it would have been an exceedingly curious thing if we could have

traced this matter any further; had the cousins intermarried, a

six-fingered variety of the human race might have been set up.

To show you that this supposition is by no means an unreasonable one, let

me now point out what took place in the case of Seth Wright's sheep, where

it happened to be a matter of moment to him to obtain a breed or raise a

flock of sheep like that accidental variety that I have described--and I

will tell you why. In that part of Massachusetts where Seth Wright was

living, the fields were separated by fences, and the sheep, which were very

active and robust, would roam abroad, and without much difficulty jump over

these fences into other people's farms. As a matter of course, this

exuberant activity on the part of the sheep constantly gave rise to all

sorts of quarrels, bickerings, and contentions among the farmers of the

neighbourhood; so it occurred to Seth Wright, who was, like his successors,

more or less 'cute, that if he could get a stock of sheep like those with

the bandy legs, they would not be able to jump over the fences so readily;

and he acted upon that idea. He killed his old ram, and as soon as the

young one arrived at maturity, he bred altogether from it. The result was

even more striking than in the human experiment which I mentioned just now.

Colonel Humphreys testifies that it always happened that the offspring were

either pure Ancons or pure ordinary sheep; that in no case was there any

mixing of the Ancons with the others. In consequence of this, in the course

of a very few years, the farmer was able to get a very considerable flock

of this variety, and a large number of them were spread throughout

Massachusetts. Most unfortunately, however--I suppose it was because they

were so common--nobody took enough notice of them to preserve their

skeletons; and although Colonel Humphreys states that he sent a skeleton to

the President of the Royal Society at the same time that he forwarded his

paper, I am afraid that the variety has entirely disappeared; for a short

time after these sheep had become prevalent in that district, the Merino

sheep were introduced; and as their wool was much more valuable, and as

they were a quiet race of sheep, and showed no tendency to trespasser jump

over fences, the Otter breed of sheep, the wool of which was inferior to

that of the Merino, was gradually allowed to die out.

You see that these facts illustrate perfectly well what may be done if you

take care to breed from stocks that are similar to each other. After having

got a variation, if, by crossing a variation with the original stock, you

multiply that variation, and then take care to keep that variation distinct

from the original stock, and make them breed together,--then you may almost

certainly produce a race whose tendency to continue the variation is

exceedingly strong.

This is what is called "selection"; and it is by exactly the same process

as that by which Seth Wright bred his Ancon sheep, that our breeds of

cattle, dogs, and fowls are obtained. There are some possibilities of

exception, but still, speaking broadly, I may say that this is the way in

which all our varied races of domestic animals have arisen; and you must

understand that it is not one peculiarity or one characteristic alone in

which animals may vary. There is not a single peculiarity or characteristic

of any kind, bodily or mental, in which offspring may not vary to a certain

extent from the parent and other animals.

Among ourselves this is well known. The simplest physical peculiarity is

mostly reproduced. I know a case of a woman who has the lobe of one of her

ears a little flattened. An ordinary observer might scarcely notice it, and

yet every one of her children has an approximation to the same peculiarity

to some extent. If you look at the other extreme, too, the gravest

diseases, such as gout, scrofula, and consumption, may be handed down with

just the same certainty and persistence as we noticed in the perpetuation

of the bandy legs of the Ancon sheep.

However, these facts are best illustrated in animals, and the extent of the

variation, as is well known, is very remarkable in dogs. For example, there

are some dogs very much smaller than others; indeed, the variation is so

enormous that probably the smallest dog would be about the size of the head

of the largest; there are very great variations in the structural forms not

only of the skeleton but also in the shape of the skull, and in the

proportions of the face and the disposition of the teeth.

The Pointer, the Retriever, Bulldog, and the Terrier differ very greatly,

and yet there is every reason to believe that every one of these races has

arisen from the same source,--that all the most important races have arisen

by this selective breeding from accidental variation.

A still more striking case of what may be done by selective breeding, and

it is a better case, because there is no chance of that partial infusion of

error to which I alluded, has been studied very carefully by Mr.

Darwin,--the case of the domestic pigeons. I dare say there may be some

among you who may be pigeon _fanciers_, and I wish you to understand

that in approaching the subject, I would speak with all humility and

hesitation, as I regret to say that I am not a pigeon fancier. I know it is

a great art and mystery, and a thing upon which a man must not speak

lightly; but I shall endeavour, as far as my understanding goes, to give

you a summary of the published and unpublished information which I have

gained from Mr. Darwin.

Among the enormous variety,--I believe there are somewhere about a hundred

and fifty kinds of pigeons,--there are four kinds which may be selected as

representing the extremest divergences of one kind from another. Their

names are the Carrier, the Pouter, the Fantail, and the Tumbler. In these

large diagrams that I have here they are each represented in their relative

sizes to each other. This first one is the Carrier; you will notice this

large excrescence on its beak; it has a comparatively small head; there is

a bare space round the eyes; it has a long neck, a very long beak, very

strong legs, large feet, long wings, and so on. The second one is the

Pouter, a very large bird, with very long legs and beak. It is called the

Pouter because it is in the habit of causing its gullet to swell up by

inflating it with air. I should tell you that all pigeons have a tendency

to do this at times, but in the Pouter it is carried to an enormous extent.

The birds appear to be quite proud of their power of swelling and puffing

themselves out in this way; and I think it is about as droll a sight as you

can well see to look at a cage full of these pigeons puffing and blowing

themselves out in this ridiculous manner.

This diagram is a representation of the third kind I mentioned--the

Fantail. It is, you see, a small bird, with exceedingly small legs and a

very small beak. It is most curiously distinguished by the size and extent

of its tail, which, instead of containing twelve feathers, may have many

more,--say thirty, or even more--I believe there are some with as many as

forty-two. This bird has a curious habit of spreading out the feathers of

its tail in such a way that they reach forward and touch its head; and if

this can be accomplished, I believe it is looked upon as a point of great

beauty.

But here is the last great variety,--the Tumbler; and of that great

variety, one of the principal kinds, and one most prized, is the specimen

represented here--the short-faced Tumbler. Its beak, you see, is reduced to

a mere nothing. Just compare the beak of this one and that of the first

one, the Carrier--I believe the orthodox comparison of the head and beak of

a thoroughly well-bred Tumbler is to stick an oat into a cherry, and that

will give you the proper relative proportions of the beak and head. The

feet and legs are exceedingly small, and the bird appears to be quite a

dwarf when placed side by side with this great Carrier.

These are differences enough in regard to their external appearance; but

these differences are by no means the whole or even the most important of

the differences which obtain between these birds. There is hardly a single

point of their structure which has not become more or less altered; and to

give you an idea of how extensive these alterations are, I have here some

very good skeletons, for which I am indebted to my friend, Mr. Tegetmeier,

a great authority in these matters; by means of which, if you examine them

by and by, you will be able to see the enormous difference in their bony

structures.

I had the privilege, some time ago, of access to some important MSS. of Mr.

Darwin, who, I may tell you, has taken very great pains and spent much

valuable time and attention on the investigation of these variations, and

getting together all the facts that bear upon them. I obtained from these

MSS. the following summary of the differences between the domestic breeds

of pigeons; that is to say, a notification of the various points in which

their organisation differs. In the first place, the back of the skull may

differ a good deal, and the development of the bones of the face may vary a

great deal; the back varies a good deal; the shape of the lower jaw varies;

the tongue varies very greatly, not only in correlation to the length and

size of the beak, but it seems also to have a kind of independent variation

of its own. Then the amount of naked skin round the eyes, and at the base

of the beak, may vary enormously; so may the length of the eyelids, the

shape of the nostrils, and the length of the neck. I have already noticed

the habit of blowing out the gullet, so remarkable in the Pouter, and

comparatively so in the others. There are great differences, too, in the

size of the female and the male, the shape of the body, the number and

width of the processes of the ribs, the development of the ribs, and the

size, shape, and development of the breastbone. We may notice, too--and I

mention the fact because it has been disputed by what is assumed to be high

authority,--the variation in the number of the sacral vertebrae. The number

of these varies from eleven to fourteen, and that without any diminution in

the number of the vertebrae of the back or of the tail. Then the number and

position of the tail-feathers may vary enormously, and so may the number of

the primary and secondary feathers of the wings. Again, the length of the

feet and of the beak,--although they have no relation to each other, yet

appear to go together,--that is, you have a long beak wherever you have

long feet. There are differences also in the periods of the acquirement of

the perfect plumage--the size and shape of the eggs--the nature of flight,

and the powers of flight--so-called _"homing"_ birds having enormous

flying powers; [Footnote: The _"Carrier,"_ I learn from Mr.

Tegetmeier, does not _carry_; a high-bred bird of this breed being but

a poor flier. The birds which fly long distances, and come home--"homing"

birds-and are consequently used as carriers, are not "carriers" in the

fancy sense.] while, on the other hand, the little Tumbler is so called

because of its extraordinary faculty of turning head over heels in the air,

instead of pursuing a direct course. And, lastly, the dispositions and

voices of the birds may vary. Thus the case of the pigeons shows you that

there is hardly a single particular--whether of instinct, or habit, or bony

structure, or of plumage--of either the internal economy or the external

shape, in which some variation or change may not take place, which, by

selective breeding, may become perpetuated, and form the foundation of, and

give rise to, a new race.

If you carry in your mind's eye these four varieties of pigeons, you will

bear with you as good a notion as you can have, perhaps, of the enormous

extent to which a deviation from a primitive type may be carried by means

of this process of selective breeding.

V. THE CONDITIONS OF EXISTENCE AS AFFECTING THE PERPETUATION OF LIVING

BEINGS

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 vertebras 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. [Footnote: 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.] 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 or 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 Mongol 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°,--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

first two, 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 square miles--the )

dry surface of the earth x )

27,878,400--the number of ) = sq. ft. 1,421,798,400,000,000

sq. ft. in 1 sq. mile ) ---------------------

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 ate 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 develop 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 larvæ and eggs. The

field mice are amazingly fond of the honey and larvæ; 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 larvæ of the bees--the cats are

therefore the INDIRECT HELPERS of the bees. [Footnote: The humble bees, on

the other hand, are direct helpers of some plants, such as the heartsease

and red clover, which are fertilised 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.] 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.

VI. A CRITICAL EXAMINATION OF THE POSITION OF MR. DARWIN'S WORK, "ON THE

ORIGIN OF SPECIES," IN RELATION TO THE COMPLETE THEORY OF THE CAUSES OF THE

PHENOMENA OF ORGANIC NATURE

In the preceding five lectures I have endeavoured to give you an account of

those facts, and of those reasonings from facts, which form the data upon

which all theories regarding the causes of the phenomena of organic nature

must be based. And, although I have had frequent occasion to quote Mr.

Darwin--as all persons hereafter, in speaking upon these subjects, will

have occasion to quote his famous book on the "Origin of Species,"--you

must yet remember that, wherever I have quoted him, it has not been upon

theoretical points, or for statements in any way connected with his

particular speculations, but on matters of fact, brought forward by

himself, or collected by himself, and which appear incidentally in his

book. If a man _will_ make a book, professing to discuss a single

question, an encyclopædia, I cannot help it.

Now, having had an opportunity of considering in this sort of way the

different statements bearing upon all theories whatsoever, I have to lay

before you, as fairly as I can, what is Mr. Darwin's view of the matter and

what position his theories hold, when judged by the principles which I have

previously laid down, as deciding our judgments upon all theories and

hypotheses.

I have already stated to you that the inquiry respecting the causes of the

phenomena of organic nature resolves itself into two problems--the first

being the question of the origination of living or organic beings; and the

second being the totally distinct problem of the modification and

perpetuation of organic beings when they have already come into existence.

The first question Mr. Darwin does not touch; he does not deal with it at

all; but he says:--"Given the origin of organic matter--supposing its

creation to have already taken place, my object is to show in consequence

of what laws and what demonstrable properties of organic matter, and of its

environments, such states of organic nature as those with which we are

acquainted must have come about." This, you will observe, is a perfectly

legitimate proposition; every person has a right to define the limits of

the inquiry which he sets before himself; and yet it is a most singular

thing that in all the multifarious, and, not unfrequently, ignorant attacks

which have been made upon the "Origin of Species," there is nothing which

has been more speciously criticised than this particular limitation. If

people have nothing else to urge against the book, they say--"Well, after

all, you see Mr. Darwin's explanation of the 'Origin of Species' is not

good for much, because, in the long run, he admits that he does not know

how organic matter began to exist. But if you admit any special creation

for the first particle of organic matter you may just as well admit it for

all the rest; five hundred or five thousand distinct creations are just as

intelligible, and just as little difficult to understand, as one." The

answer to these cavils is two-fold. In the first place, all human inquiry

must stop somewhere; all our knowledge and all our investigation cannot

take us beyond the limits set by the finite and restricted character of our

faculties, or destroy the endless unknown, which accompanies, like its

shadow, the endless procession of phenomena. So far as I can venture to

offer an opinion on such a matter, the purpose of our being in existence,

the highest object that human beings can set before themselves, is not the

pursuit of any such chimera as the annihilation of the unknown; but it is

simply the unwearied endeavour to remove its boundaries a little further

from our little sphere of action.

I wonder if any historian would for a moment admit the objection, that it

is preposterous to trouble ourselves about the history of the Roman Empire,

because we do not know anything positive about the origin and first

building of the city of Rome! Would it be a fair objection to urge,

respecting the sublime discoveries of a Newton, or a Kepler, those great

philosophers, whose discoveries have been of the profoundest benefit and

service to all men--to say to them--"After all that you have told us as to

how the planets revolve, and how they are maintained in their orbits, you

cannot tell us what is the cause of the origin of the sun, moon, and stars.

So what is the use of what you have done?" Yet these objections would not

be one whit more preposterous than the objections which have been made to

the "Origin of Species." Mr. Darwin, then, had a perfect right to limit his

inquiry as he pleased, and the only question for us--the inquiry being so

limited--is to ascertain whether the method of his inquiry is sound or

unsound; whether he has obeyed the canons which must guide and govern all

investigation, or whether he has broken them; and it was because our

inquiry this evening is essentially limited to that question, that I spent

a good deal of time in a former lecture (which, perhaps some of you thought

might have been better employed), in endeavouring to illustrate the method

and nature of scientific inquiry in general. We shall now have to put in

practice the principles that I then laid down.

I stated to you in substance, if not in words, that wherever there are

complex masses of phenomena to be inquired into, whether they be phenomena

of the affairs of daily life, or whether they belong to the more abstruse

and difficult problems laid before the philosopher, our course of

proceeding in unravelling that complex chain of phenomena with a view to

get at its cause, is always the same; in all cases we must invent an

hypothesis; we must place before ourselves some more or less likely

supposition respecting that cause; and then, having assumed an hypothesis,

having supposed a cause for the phenomena in question, we must endeavour,

on the one hand, to demonstrate our hypothesis, or, on the other, to upset

and reject it altogether, by testing it in three ways. We must, in the

first place, be prepared to prove that the supposed causes of the phenomena

exist in nature; that they are what the logicians call _vera

causæ_--true causes;--in the next place, we should be prepared to show

that the assumed causes of the phenomena are competent to produce such

phenomena as those which we wish to explain by them; and in the last place,

we ought to be able to show that no other known causes are competent to

produce these phenomena. If we can succeed in satisfying these three

conditions we shall have demonstrated our hypothesis; or rather I ought to

say we shall have proved it as far as certainty is possible for us; for,

after all, there is no one of our surest convictions which may not be

upset, or at any rate modified by a further accession of knowledge. It was

because it satisfied these conditions that we accepted the hypothesis as to

the disappearance of the tea-pot and spoons in the case I supposed in a

previous lecture; we found that our hypothesis on that subject was tenable

and valid, because the supposed cause existed in nature, because it was

competent to account for the phenomena, and because no other known cause

was competent to account for them; and it is upon similar grounds that any

hypothesis you choose to name is accepted in science as tenable and valid.

What is Mr. Darwin's hypothesis? As I apprehend it--for I have put it into

a shape more convenient for common purposes than I could find

_verbatim_ in his book--as I apprehend it, I say, it is, that all the

phenomena of organic nature, past and present, result from, or are caused

by, the inter-action of those properties of organic matter, which we have

called ATAVISM and VARIABILITY, with the CONDITIONS OF EXISTENCE, or, in

other words,--given the existence of organic matter, its tendency to

transmit its properties, and its tendency occasionally to vary; and,

lastly, given the conditions of existence by which organic matter is

surrounded--that these put together are the causes of the Present and of

the Past conditions of ORGANIC NATURE.

Such is the hypothesis as I understand it. Now let us see how it will stand

the various tests which I laid down just now. In the first place, do these

supposed causes of the phenomena exist in nature? Is it the fact that, in

nature, these properties of organic matter--atavism and variability--and

those phenomena which we have called the conditions of existence,--is it

true that they exist? Well, of course, if they do not exist, all that I

have told you in the last three or four lectures must be incorrect, because

I have been attempting to prove that they do exist, and I take it that

there is abundant evidence that they do exist; so far, therefore, the

hypothesis does not break down.

But in the next place comes a much more difficult inquiry:--Are the causes

indicated competent to give rise to the phenomena of organic nature? I

suspect that this is indubitable to a certain extent. It is demonstrable, I

think, as I have endeavoured to show you, that they are perfectly competent

to give rise to all the phenomena which are exhibited by RACES in nature.

Furthermore, I believe that they are quite competent to account for all

that we may call purely structural phenomena which are exhibited by SPECIES

in nature. On that point also I have already enlarged somewhat. Again, I

think that the causes assumed are competent to account for most of the

physiological characteristics of species, and I not only think that they

are competent to account for them, but I think that they account for many

things which otherwise remain wholly unaccountable and inexplicable, and I

may say incomprehensible. For a full exposition of the grounds on which

this conviction is based, I must refer you to Mr. Darwin's work; all that I

can do now is to illustrate what I have said by two or three cases taken

almost at random.

I drew your attention, on a previous evening, to the facts which are

embodied in our systems of Classification, which are the results of the

examination and comparison of the different members of the animal kingdom

one with another. I mentioned that the whole of the animal kingdom is

divisible into five sub-kingdoms; that each of these sub-kingdoms is again

divisible into provinces; that each province may be divided into classes,

and the classes into the successively smaller groups, orders, families,

genera, and species.

Now, in each of these groups the resemblance in structure among the members

of the group is closer in proportion as the group is smaller. Thus, a man

and a worm are members of the animal kingdom in virtue of certain

apparently slight though really fundamental resemblances which they

present. But a man and a fish are members of the same sub-kingdom

_Vertebrata_, because they are much more like one another than either

of them is to a worm, or a snail, or any member of the other sub-kingdoms.

For similar reasons men and horses are arranged as members of the same

Class, _Mammalia_; men and apes as members of the same Order,

_Primates_; and if there were any animals more like men than they were

like any of the apes, and yet different from men in important and constant

particulars of their organisation, we should rank them as members of the

same Family, or of the same Genus, but as of distinct Species.

That it is possible to arrange all the varied forms of animals into groups,

having this sort of singular subordination one to the other, is a very

remarkable circumstance; but, as Mr. Darwin remarks, this is a result which

is quite to be expected, if the principles which he lays down be correct.

Take the case of the races which are known to be produced by the operation

of atavism and variability, and the conditions of existence which check and

modify these tendencies. Take the case of the pigeons that I brought before

you: there it was shown that they might be all classed as belonging to some

one of five principal divisions, and that within these divisions other

subordinate groups might be formed. The members of these groups are related

to one another in just the same way as the genera of a family, and the

groups themselves as the families of an order, or the orders of a class;

while all have the same sort of structural relations with the wild

rock-pigeon, as the members of any great natural group have with a real or

imaginary typical form. Now, we know that all varieties of pigeons of every

kind have arisen by a process of selective breeding from a common stock,

the rock-pigeon; hence, you see, that if all species of animals have

proceeded from some common stock, the general character of their structural

relations, and of our systems of classification, which express those

relations, would be just what we find them to be. In other words, the

hypothetical cause is, so far, competent to produce effects similar to

those of the real cause.

Take, again, another set of very remarkable facts,--the existence of what

are called rudimentary organs, organs for which we can find no obvious use,

in the particular animal economy in which they are found, and yet which are

there.

Such are the splint-like bones in the leg of the horse, which I here show

you, and which correspond with bones which belong to certain toes and

fingers in the human hand and foot. In the horse you see they are quite

rudimentary, and bear neither toes nor fingers; so that the horse has only

one "finger" in his fore-foot and one "toe" in his hind-foot. But it is a

very curious thing that the animals closely allied to the horse show more

toes than he; as the rhinoceros, for instance: he has these extra toes well

formed, and anatomical facts show very clearly that he is very closely

related to the horse indeed. So we may say that animals, in an anatomical

sense nearly related to the horse, have those parts which are rudimentary

in him fully developed.

Again, the sheep and the cow have no cutting-teeth, but only a hard pad in

the upper jaw. That is the common characteristic of ruminants in general.

But the calf has in its upper jaw some rudiments of teeth which never are

developed, and never play the part of teeth at all. Well, if you go back in

time, you find some of the older, now extinct, allies of the ruminants have

well-developed teeth in their upper jaws; and at the present day the pig

(which is in structure closely connected with ruminants) has well-developed

teeth in its upper jaw; so that here is another instance of organs

well-developed and very useful, in one animal, represented by rudimentary

organs, for which we can discover no purpose whatsoever in another closely

allied animal. The whalebone whale, again, has horny "whalebone" plates in

its mouth, and no teeth; but the young foetal whale before it is born has

teeth in its jaws; they, however, are never used, and they never come to

anything. But other members of the group to which the whale belongs have

well-developed teeth in both jaws.

Upon any hypothesis of special creation, facts of this kind appear to me to

be entirely unaccountable and inexplicable, but they cease to be so if you

accept Mr. Darwin's hypothesis, and see reason for believing that the

whalebone whale and the whale with teeth in its mouth both sprang from a

whale that had teeth, and that the teeth of the foetal whale are merely

remnants--recollections, if we may so say--of the extinct whale. So in the

case of the horse and the rhinoceros: suppose that both have descended by

modification from some earlier form which had the normal number of toes,

and the persistence of the rudimentary bones which no longer support toes

in the horse becomes comprehensible.

In the language that we speak in England, and in the language of the

Greeks, there are identical verbal roots, or elements entering into the

composition of words. That fact remains unintelligible so long as we

suppose English and Greek to be independently created tongues; but when it

is shown that both languages are descended from one original, we give an

explanation of that resemblance. In the same way the existence of identical

structural roots, if I may so term them, entering into the composition of

widely different animals, is striking evidence in favour of the descent of

those animals from a common original.

To turn to another kind of illustration:--If you regard the whole series of

stratified rocks--that enormous thickness of sixty or seventy thousand feet

that I have mentioned before, constituting the only record we have of a

most prodigious lapse of time, that time being, in all probability, but a

fraction of that of which we have no record;--if you observe in these

successive strata of rocks successive groups of animals arising and dying

out, a constant succession, giving you the same kind of impression, as you

travel from one group of strata to another, as you would have in travelling

from one country to another;--when you find this constant succession of

forms, their traces obliterated except to the man of science--when you look

at this wonderful history, and ask what it means, it is only a paltering

with words if you are offered the reply--"They were so created."

But if, on the other hand, you look on all forms of organised beings as the

results of the gradual modification of a primitive type, the facts receive

a meaning, and you see that these older conditions are the necessary

predecessors of the present. Viewed in this light the facts of

palaeontology receive a meaning--upon any other hypothesis I am unable to

see, in the slightest degree, what knowledge or signification we are to

draw out of them. Again, note as bearing upon the same point, the singular

likeness which obtains between the successive Faunæ and Floræ, whose

remains are preserved on the rocks: you never find any great and enormous

difference between the immediately successive Faunæ and Floræ, unless you

have reason to believe there has also been a great lapse of time or a great

change of conditions. The animals, for instance, of the newest tertiary

rocks, in any part of the world, are always, and without exception, found

to be closely allied with those which now live in that part of the world.

For example, in Europe, Asia, and Africa, the large mammals are at present

rhinoceroses, hippopotamuses, elephants, lions, tigers, oxen, horses, &c.;

and if you examine the newest tertiary deposits, which contain the animals

and plants which immediately preceded those which now exist in the same

country, you do not find gigantic specimens of ant-eaters and kangaroos,

but you find rhinoceroses, elephants, lions, tigers, &c.,--of different

species to those now living--but still their close allies. If you turn to

South America, where, at the present day, we have great sloths and

armadilloes and creatures of that kind, what do you find in the newest

tertiaries? You find the great sloth-like creature, the _Megatherium_,

and the great armadillo, the _Glyptodon_, and so on. And if you go to

Australia you find the same law holds good, namely, that that condition of

organic nature which has preceded the one which now exists, presents

differences perhaps of species, and of genera, but that the great types of

organic structure are the same as those which now flourish.

What meaning has this fact upon any other hypothesis or supposition than

one of successive modification? But if the population of the world, in any

age, is the result of the gradual modification of the forms which peopled

it in the preceding age--if that has been the case, it is intelligible

enough; because we may expect that the creature that results from the

modification of an elephantine mammal shall be something like an elephant,

and the creature which is produced by the modification of an armadillo-like

mammal shall be like an armadillo. Upon that supposition, I say, the facts

are intelligible; upon any other, that I am aware of, they are not.

So far, the facts of palæontology are consistent with almost any form of

the doctrine of progressive modification; they would not be absolutely

inconsistent with the wild speculations of De Maillet, or with the less

objectionable hypothesis of Lamarck. But Mr. Darwin's views have one

peculiar merit; and that is, that they are perfectly consistent with an

array of facts which are utterly inconsistent with, and fatal to, any other

hypothesis of progressive modification which has yet been advanced. It is

one remarkable peculiarity of Mr. Darwin's hypothesis that it involves no

necessary progression or incessant modification, and that it is perfectly

consistent with the persistence for any length of time of a given primitive

stock, contemporaneously with its modifications. To return to the case of

the domestic breeds of pigeons, for example; you have the dove-cot pigeon,

which closely resembles the rock pigeon, from which they all started,

existing at the same time with the others. And if species are developed in

the same way in nature, a primitive stock and its modifications may,

occasionally, all find the conditions fitted for their existence; and

though they come into competition, to a certain extent, with one another,

the derivative species may not necessarily extirpate the primitive one, or

_vice versa_.

Now palæontology shows us many facts which are perfectly harmonious with

these observed effects of the process by which Mr. Darwin supposes species

to have originated, but which appear to me to be totally inconsistent with

any other hypothesis which has been proposed. There are some groups of

animals and plants, in the fossil world, which have been said to belong to

"persistent types," because they have persisted, with very little change

indeed, through a very great range of time, while everything about them has

changed largely. There are families of fishes whose type of construction

has persisted all the way from the carboniferous strata right up to the

cretaceous; and others which have lasted through almost the whole range of

the secondary rocks, and from the lias to the older tertiaries. It is

something stupendous this--to consider a genus lasting without essential

modifications through all this enormous lapse of time while almost

everything else was changed and modified.

Thus I have no doubt that Mr. Darwin's hypothesis will be found competent

to explain the majority of the phenomena exhibited by species in nature;

but in an earlier lecture I spoke cautiously with respect to its power of

explaining all the physiological peculiarities of species.

There is, in fact, one set of these peculiarities which the theory of

selective modification, as it stands at present, is not wholly competent to

explain, and that is the group of phenomena which I mentioned to you under

the name of Hybridism, and which I explained to consist in the sterility of

the offspring of certain species when crossed one with another. It matters

not one whit whether this sterility is universal, or whether it exists only

in a single case. Every hypothesis is bound to explain, or, at any rate,

not be inconsistent with, the whole of the facts which it professes to

account for; and if there is a single one of these facts which can be shown

to be inconsistent with (I do not merely mean inexplicable by, but contrary

to) the hypothesis, the hypothesis falls to the ground,--it is worth

nothing. One fact with which it is positively inconsistent is worth as

much, and as powerful in negativing the hypothesis, as five hundred. If I

am right in thus defining the obligations of an hypothesis, Mr. Darwin, in

order to place his views beyond the reach of all possible assault, ought to

be able to demonstrate the possibility of developing from a particular

stock by selective breeding, two forms, which should either be unable to

cross one with another, or whose cross-bred offspring should be infertile

with one another.

For, you see, if you have not done that you have not strictly fulfilled all

the conditions of the problem; you have not shown that you can produce, by

the cause assumed, all the phenomena which you have in nature. Here are the

phenomena of Hybridism staring you in the face, and you cannot say, "I can,

by selective modification, produce these same results." Now, it is admitted

on all hands that, at present, so far as experiments have gone, it has not

been found possible to produce this complete physiological divergence by

selective breeding. I stated this very clearly before, and I now refer to

the point, because, if it could be proved, not only that this _has_

not been done, but that it _cannot_ be done; if it could be

demonstrated that it is impossible to breed selectively, from any stock, a

form which shall not breed with another, produced from the same stock; and

if we were shown that this must be the necessary and inevitable results of

all experiments, I hold that Mr. Darwin's hypothesis would be utterly

shattered.

But has this been done? or what is really the state of the case? It is

simply that, so far as we have gone yet with our breeding, we have not

produced from a common stock two breeds which are not more or less fertile

with one another.

I do not know that there is a single fact which would justify any one in

saying that any degree of sterility has been observed between breeds

absolutely known to have been produced by selective breeding from a common

stock. On the other hand, I do not know that there is a single fact which

can justify any one in asserting that such sterility cannot be produced by

proper experimentation. For my own part, I see every reason to believe that

it may, and will be so produced. For, as Mr. Darwin has very properly

urged, when we consider the phenomena of sterility, we find they are most

capricious; we do not know what it is that the sterility depends on. There

are some animals which will not breed in captivity; whether it arises from

the simple fact of their being shut up and deprived of their liberty, or

not, we do not know, but they certainly will not breed. What an astounding

thing this is, to find one of the most important of all functions

annihilated by mere imprisonment!

So, again, there are cases known of animals which have been thought by

naturalists to be undoubted species, which have yielded perfectly fertile

hybrids; while there are other species which present what everybody

believes to be varieties [Footnote: And as I conceive with very good

reason; but if any objector urges that we cannot prove that they have been

produced by artificial or natural selection, the objection must be

admitted--ultra-sceptical as it is. But in science, scepticism is a duty.]

which are more or less infertile with one another. There are other cases

which are truly extraordinary; there is one, for example, which has been

carefully examined,--of two kinds of sea-weed, of which the male element of

the one, which we may call A, fertilises the female element of the other,

B; while the male element of B will not fertilise the female element of A;

so that, while the former experiment seems to show us that they are

_varieties_, the latter leads to the conviction that they are

_species_.

When we see how capricious and uncertain this sterility is, how unknown the

conditions on which it depends, I say that we have no right to affirm that

those conditions will not be better understood by and by, and we have no

ground for supposing that we may not be able to experiment so as to obtain

that crucial result which I mentioned just now. So that though Mr. Darwin's

hypothesis does not completely extricate us from this difficulty at

present, we have not the least right to say it will not do so.

There is a wide gulf between the thing you cannot explain and the thing

that upsets you altogether. There is hardly any hypothesis in this world

which has not some fact in connection with it which has not been explained,

but that is a very different affair to a fact that entirely opposes your

hypothesis; in this case all you can say is, that your hypothesis is in the

same position as a good many others.

Now, as to the third test, that there are no other causes competent to

explain the phenomena, I explained to you that one should be able to say of

an hypothesis, that no other known causes than those supposed by it are

competent to give rise to the phenomena. Here, I think, Mr. Darwin's view

is pretty strong. I really believe that the alternative is either Darwinism

or nothing, for I do not know of any rational conception or theory of the

organic universe which has any scientific position at all beside Mr.

Darwin's. I do not know of any proposition that has been put before us with

the intention of explaining the phenomena of organic nature, which has in

its favour a thousandth part of the evidence which may be adduced in favour

of Mr. Darwin's views. Whatever may be the objections to his views,

certainly all other theories are absolutely out of court.

Take the Lamarckian hypothesis, for example. Lamarck was a great

naturalist, and to a certain extent went the right way to work; he argued

from what was undoubtedly a true cause of some of the phenomena of organic

nature. He said it is a matter of experience that an animal may be modified

more or less in consequence of its desires and consequent actions. Thus, if

a man exercise himself as a blacksmith, his arms will become strong and

muscular; such organic modification is a result of this particular action

and exercise. Lamarck thought that by a very simple supposition based on

this truth he could explain the origin of the various animal species: he

said, for example, that the short-legged birds which live on fish had been

converted into the long-legged waders by desiring to get the fish without

wetting their feathers, and so stretching their legs more and more through

successive generations. If Lamarck could have shown experimentally that

even races of animals could be produced in this way, there might have been

some ground for his speculations. But he could show nothing of the kind,

and his hypothesis has pretty well dropped into oblivion, as it deserved to

do. I said in an earlier lecture that there are hypotheses and hypotheses,

and when people tell you that Mr. Darwin's strongly-based hypothesis is

nothing but a mere modification of Lamarck's, you will know what to think

of their capacity for forming a judgment on this subject.

But you must recollect that when I say I think it is either Mr. Darwin's

hypothesis or nothing; that either we must take his view, or look upon the

whole of organic nature as an enigma, the meaning of which is wholly hidden

from us; you must understand that I mean that I accept it provisionally, in

exactly the same way as I accept any other hypothesis. Men of science do

not pledge themselves to creeds; they are bound by articles of no sort;

there is not a single belief that it is not a bounden duty with them to

hold with a light hand and to part with cheerfully, the moment it is really

proved to be contrary to any fact, great or small. And if, in course of

time I see good reasons for such a proceeding, I shall have no hesitation

in coming before you, and pointing out any change in my opinion without

finding the slightest occasion to blush for so doing. So I say that we

accept this view as we accept any other, so long as it will help us, and we

feel bound to retain it only so long as it will serve our great

purpose--the improvement of Man's estate and the widening of his knowledge.

The moment this, or any other conception, ceases to be useful for these

purposes, away with it to the four winds; we care not what becomes of it!

But to say truth, although it has been my business to attend closely to the

controversies roused by the publication of Mr. Darwin's book, I think that

not one of the enormous mass of objections and obstacles which have been

raised is of any very great value, except that sterility case which I

brought before you just now. All the rest are misunderstandings of some

sort, arising either from prejudice, or want of knowledge, or still more

from want of patience and care in reading the work.

For you must recollect that it is not a book to be read with as much ease

as its pleasant style may lead you to imagine. You spin through it as if it

were a novel the first time you read it, and think you know all about it;

the second time you read it you think you know rather less about it; and

the third time, you are amazed to find how little you have really

apprehended its vast scope and objects. I can positively say that I never

take it up without finding in it some new view, or light, or suggestion

that I have not noticed before. That is the best characteristic of a

thorough and profound book; and I believe this feature of the "Origin of

Species" explains why so many persons have ventured to pass judgment and

criticisms upon it which are by no means worth the paper they are written

on.

Before concluding these lectures there is one point to which I must

advert--though, as Mr. Darwin has said nothing about man in his book, it

concerns myself rather than him;--for I have strongly maintained on sundry

occasions that if Mr. Darwin's views are sound, they apply as much to man

as to the lower mammals, seeing that it is perfectly demonstrable that the

structural differences which separate man from the apes are not greater

than those which separate some apes from others. There cannot be the

slightest doubt in the world that the argument which applies to the

improvement of the horse from an earlier stock, or of ape from ape, applies

to the improvement of man from some simpler and lower stock than man. There

is not a single faculty--functional or structural, moral, intellectual, or

instinctive, there--is no faculty whatever that is not capable of

improvement; there is no faculty whatsoever which does not depend upon

structure, and as structure tends to vary, it is capable of being improved.

Well, I have taken a good deal of pains at various times to prove this, and

I have endeavoured to meet the objections of those who maintain, that the

structural differences between man and the lower animals are of so vast a

character and enormous extent, that even if Mr. Darwin's views are correct,

you cannot imagine this particular modification to take place. It is, in

fact, an easy matter to prove that, so far as structure is concerned, man

differs to no greater extent from the animals which are immediately below

him than these do from other members of the same order. Upon the other

hand, there is no one who estimates more highly than I do the dignity of

human nature, and the width of the gulf in intellectual and moral matters

which lies between man and the whole of the lower creation.

But I find this very argument brought forward vehemently by some. "You say

that man has proceeded from a modification of some lower animal, and you

take pains to prove that the structural differences which are said to exist

in his brain do not exist at all, and you teach that all functions,

intellectual, moral, and others, are the expression or the result, in the

long run, of structures, and of the molecular forces which they exert." It

is quite true that I do so.

"Well, but," I am told at once, somewhat triumphantly, "you say in the same

breath that there is a great moral and intellectual chasm between man and

the lower animals. How is this possible when you declare that moral and

intellectual characteristics depend on structure, and yet tell us that

there is no such gulf between the structure of man and that of the lower

animals?"

I think that objection is based upon a misconception of the real relations

which exist between structure and function, between mechanism and work.

Function is the expression of molecular forces and arrangements no doubt;

but, does it follow from this, that variation in function so depends upon

variation in structure that the former is always exactly proportioned to

the latter? If there is no such relation, if the variation in function

which follows on a variation in structure may be enormously greater than

the variation of the structure, then, you see, the objection falls to the

ground.

Take a couple of watches--made by the same maker, and as completely alike

as possible; set them upon the table, and the function of each--which is

its rate of going--will be performed in the same manner, and you shall be

able to distinguish no difference between them; but let me take a pair of

pincers, and if my hand is steady enough to do it, let me just lightly

crush together the bearings of the balance-wheel, or force to a slightly

different angle the teeth of the escapement of one of them, and of course

you know the immediate result will be that the watch, so treated, from that

moment will cease to go. But what proportion is there between the

structural alteration and the functional result? Is it not perfectly

obvious that the alteration is of the minutest kind, yet that, slight as it

is, it has produced an infinite difference in the performance of the

functions of these two instruments?

Well, now, apply that to the present question. What is it that constitutes

and makes man what he is? What is it but his power of language--that

language giving him the means of recording his experience--making every

generation somewhat wiser than its predecessor--more in accordance with the

established order of the universe?

What is it but this power of speech, of recording experience, which enables

men to be men--looking before and after and, in some dim sense,

understanding the working of this wondrous universe--and which

distinguishes man from the whole of the brute world? I say that this

functional difference is vast, unfathomable, and truly infinite in its

consequences; and I say at the same time, that it may depend upon

structural differences which shall be absolutely inappreciable to us with

our present means of investigation. What is this very speech that we are

talking about? I am speaking to you at this moment, but if you were to

alter, in the minutest degree, the proportion of the nervous forces now

active in the two nerves which supply the muscles of my glottis, I should

become suddenly dumb. The voice is produced only so long as the vocal

chords are parallel; and these are parallel only so long as certain muscles

contract with exact equality; and that again depends on the equality of

action of those two nerves I spoke of. So that a change of the minutest

kind in the structure of one of these nerves, or in the structure of the

part in which it originates, or of the supply of blood to that part, or of

one of the muscles to which it is distributed, might render all of us dumb.

But a race of dumb men, deprived of all communication with those who could

speak, would be little indeed removed from the brutes. And the moral and

intellectual difference between them and ourselves would be practically

infinite, though the naturalist should not be able to find a single shadow

of even specific structural difference.

But let me dismiss this question now, and, in conclusion, let me say that

you may go away with it as my mature conviction, that Mr. Darwin's work is

the greatest contribution which has been made to biological science since

the publication of the "Regne Animal" of Cuvier, and since that of the

"History of Development," of Von Baer. I believe that if you strip it of

its theoretical part it still remains one of the greatest encyclopaedias of

biological doctrine that any one man ever brought forth; and I believe

that, if you take it as the embodiment of an hypothesis, it is destined to

be the guide of biological and psychological speculation for the next three

or four generations.