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Huxley + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +The Project Gutenberg EBook of The Perpetuation Of Living Beings, +Hereditary Transmission And Variation, by Thomas H. Huxley + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Perpetuation Of Living Beings, Hereditary Transmission And Variation + Lecture IV. (of VI.), Lectures To Working Men, at the + Museum of Practical Geology, 1863, On Darwin's work: "Origin + of Species". + +Author: Thomas H. Huxley + +Release Date: January 4, 2009 [EBook #2924] +Last Updated: January 22, 2013 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HEREDITARY TRANSMISSION *** + + + + +Produced by Amy E. Zelmer, and David Widger + + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + THE PERPETUATION OF LIVING BEINGS, HEREDITARY TRANSMISSION AND VARIATION + </h1> + <p> + <br /> + </p> + <h3> + Lecture III. (of VI.), "Lectures To Working Men", at the Museum of + Practical Geology, 1863, On Darwin's work: "Origin of Species". + </h3> + <p> + <br /><br /> + </p> + <h2> + By Thomas H. Huxley + </h2> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <p> + The inquiry which we undertook, at our last meeting, into the state of our + knowledge of the causes of the phenomena of organic nature,—of the + past and of the present,—resolved itself into two subsidiary + inquiries: the first was, whether we know anything, either historically or + experimentally, of the mode of origin of living beings; the second + subsidiary inquiry was, whether, granting the origin, we know anything + about the perpetuation and modifications of the forms of organic beings. + The reply which I had to give to the first question was altogether + negative, and the chief result of my last lecture was, that, neither + historically nor experimentally, do we at present know anything whatsoever + about the origin of living forms. We saw that, historically, we are not + likely to know anything about it, although we may perhaps learn something + experimentally; but that at present we are an enormous distance from the + goal I indicated. + </p> + <p> + I now, then, take up the next question, What do we know of the + reproduction, the perpetuation, and the modifications of the forms of + living beings, supposing that we have put the question as to their + origination on one side, and have assumed that at present the causes of + their origination are beyond us, and that we know nothing about them? Upon + this question the state of our knowledge is extremely different; it is + exceedingly large, and, if not complete, our experience is certainly most + extensive. It would be impossible to lay it all before you, and the most I + can do, or need do to-night, is to take up the principal points and put + them before you with such prominence as may subserve the purposes of our + present argument. + </p> + <p> + The method of the perpetuation of organic beings is of two kinds,—the + asexual and the sexual. In the first the perpetuation takes place from and + by a particular act of an individual organism, which sometimes may not be + classed as belonging to any sex at all. In the second case, it is in + consequence of the mutual action and interaction of certain portions of + the organisms of usually two distinct individuals,—the male and the + female. The cases of asexual perpetuation are by no means so common as the + cases of sexual perpetuation; and they are by no means so common in the + animal as in the vegetable world. You are all probably familiar with the + fact, as a matter of experience, that you can propagate plants by means of + what are called "cuttings;" for example, that by taking a cutting from a + geranium plant, and rearing it properly, by supplying it with light and + warmth and nourishment from the earth, it grows up and takes the form of + its parent, having all the properties and peculiarities of the original + plant. + </p> + <p> + Sometimes this process, which the gardener performs artificially, takes + place naturally; that is to say, a little bulb, or portion of the plant, + detaches itself, drops off, and becomes capable of growing as a separate + thing. That is the case with many bulbous plants, which throw off in this + way secondary bulbs, which are lodged in the ground and become developed + into plants. This is an asexual process, and from it results the + repetition or reproduction of the form of the original being from which + the bulb proceeds. + </p> + <p> + Among animals the same thing takes place. Among the lower forms of animal + life, the infusorial animalculae we have already spoken of throw off + certain portions, or break themselves up in various directions, sometimes + transversely or sometimes longitudinally; or they may give off buds, which + detach themselves and develop into their proper forms. There is the common + fresh-water Polype, for instance, which multiplies itself in this way. + Just in the same way as the gardener is able to multiply and reproduce the + peculiarities and characters of particular plants by means of cuttings, so + can the physiological experimentalist—as was shown by the Abbe + Trembley many years ago—so can he do the same thing with many of the + lower forms of animal life. M. de Trembley showed that you could take a + polype and cut it into two, or four, or many pieces, mutilating it in all + directions, and the pieces would still grow up and reproduce completely + the original form of the animal. These are all cases of asexual + multiplication, and there are other instances, and still more + extraordinary ones, in which this process takes place naturally, in a more + hidden, a more recondite kind of way. You are all of you familiar with + those little green insects, the 'Aphis' or blight, as it is called. These + little animals, during a very considerable part of their existence, + multiply themselves by means of a kind of internal budding, the buds being + developed into essentially asexual animals, which are neither male nor + female; they become converted into young 'Aphides', which repeat the + process, and their offspring after them, and so on again; you may go on + for nine or ten, or even twenty or more successions; and there is no very + good reason to say how soon it might terminate, or how long it might not + go on if the proper conditions of warmth and nourishment were kept up. + </p> + <p> + Sexual reproduction is quite a distinct matter. Here, in all these cases, + what is required is the detachment of two portions of the parental + organisms, which portions we know as the egg and the spermatozoon. In + plants it is the ovule and the pollen-grain, as in the flowering plants, + or the ovule and the antherozooid, as in the flowerless. Among all forms + of animal life, the spermatozoa proceed from the male sex, and the egg is + the product of the female. Now, what is remarkable about this mode of + reproduction is this, that the egg by itself, or the spermatozoa by + themselves, are unable to assume the parental form; but if they be brought + into contact with one another, the effect of the mixture of organic + substances proceeding from two sources appears to confer an altogether new + vigour to the mixed product. This process is brought about, as we all + know, by the sexual intercourse of the two sexes, and is called the act of + impregnation. The result of this act on the part of the male and female + is, that the formation of a new being is set up in the ovule or egg; this + ovule or egg soon begins to be divided and subdivided, and to be fashioned + into various complex organisms, and eventually to develop into the form of + one of its parents, as I explained in the first lecture. These are the + processes by which the perpetuation of organic beings is secured. Why + there should be the two modes—why this re-invigoration should be + required on the part of the female element we do not know; but it is most + assuredly the fact, and it is presumable, that, however long the process + of asexual multiplication could be continued, I say there is good reason + to believe that it would come to an end if a new commencement were not + obtained by a conjunction of the two sexual elements. + </p> + <p> + That character which is common to these two distinct processes is this, + that, whether we consider the reproduction, or perpetuation, or + modification of organic beings as they take place asexually, or as they + may take place sexually,—in either case, I say, the offspring has a + constant tendency to assume, speaking generally, the character of the + parent. As I said just now, if you take a slip of a plant, and tend it + with care, it will eventually grow up and develop into a plant like that + from which it had sprung; and this tendency is so strong that, as + gardeners know, this mode of multiplying by means of cuttings is the only + secure mode of propagating very many varieties of plants; the peculiarity + of the primitive stock seems to be better preserved if you propagate it by + means of a slip than if you resort to the sexual mode. + </p> + <p> + Again, in experiments upon the lower animals, such as the polype, to which + I have referred, it is most extraordinary that, although cut up into + various pieces, each particular piece will grow up into the form of the + primitive stock; the head, if separated, will reproduce the body and the + tail; and if you cut off the tail, you will find that that will reproduce + the body and all the rest of the members, without in any way deviating + from the plan of the organism from which these portions have been + detached. And so far does this go, that some experimentalists have + carefully examined the lower orders of animals,—among them the Abbe + Spallanzani, who made a number of experiments upon snails and salamanders,—and + have found that they might mutilate them to an incredible extent; that you + might cut off the jaw or the greater part of the head, or the leg or the + tail, and repeat the experiment several times, perhaps, cutting off the + same member again and again; and yet each of those types would be + reproduced according to the primitive type: nature making no mistake, + never putting on a fresh kind of leg, or head, or tail, but always tending + to repeat and to return to the primitive type. + </p> + <p> + It is the same in sexual reproduction: it is a matter of perfectly common + experience, that the tendency on the part of the offspring always is, + speaking broadly, to reproduce the form of the parents. The proverb has it + that the thistle does not bring forth grapes; so, among ourselves, there + is always a likeness, more or less marked and distinct, between children + and their parents. That is a matter of familiar and ordinary observation. + We notice the same thing occurring in the cases of the domestic animals—dogs, + for instance, and their offspring. In all these cases of propagation and + perpetuation, there seems to be a tendency in the offspring to take the + characters of the parental organisms. To that tendency a special name is + given—it is called 'Atavism', it expresses this tendency to revert + to the ancestral type, and comes from the Latin word 'atavus', ancestor. + </p> + <p> + Well, this 'Atavism' which I shall speak of, is, as I said before, one of + the most marked and striking tendencies of organic beings; but, side by + side with this hereditary tendency there is an equally distinct and + remarkable tendency to variation. The tendency to reproduce the original + stock has, as it were, its limits, and side by side with it there is a + tendency to vary in certain directions, as if there were two opposing + powers working upon the organic being, one tending to take it in a + straight line, and the other tending to make it diverge from that straight + line, first to one side and then to the other. + </p> + <p> + So that you see these two tendencies need not precisely contradict one + another, as the ultimate result may not always be very remote from what + would have been the case if the line had been quite straight. + </p> + <p> + This tendency to variation is less marked in that mode of propagation + which takes place asexually; it is in that mode that the minor characters + of animal and vegetable structures are most completely preserved. Still, + it will happen sometimes, that the gardener, when he has planted a cutting + of some favourite plant, will find, contrary to his expectation, that the + slip grows up a little different from the primitive stock—that it + produces flowers of a different colour or make, or some deviation in one + way or another. This is what is called the 'sporting' of plants. + </p> + <p> + In animals the phenomena of asexual propagation are so obscure, that at + present we cannot be said to know much about them; but if we turn to that + mode of perpetuation which results from the sexual process, then we find + variation a perfectly constant occurrence, to a certain extent; and, + indeed, I think that a certain amount of variation from the primitive + stock is the necessary result of the method of sexual propagation itself; + for, inasmuch as the thing propagated proceeds from two organisms of + different sexes and different makes and temperaments, and as the offspring + is to be either of one sex or the other, it is quite clear that it cannot + be an exact diagonal of the two, or it would be of no sex at all; it + cannot be an exact intermediate form between that of each of its parents—it + must deviate to one side or the other. You do not find that the male + follows the precise type of the male parent, nor does the female always + inherit the precise characteristics of the mother,—there is always a + proportion of the female character in the male offspring, and of the male + character in the female offspring. That must be quite plain to all of you + who have looked at all attentively on your own children or those of your + neighbours; you will have noticed how very often it may happen that the + son shall exhibit the maternal type of character, or the daughter possess + the characteristics of the father's family. There are all sorts of + intermixtures and intermediate conditions between the two, where + complexion, or beauty, or fifty other different peculiarities belonging to + either side of the house, are reproduced in other members of the same + family. Indeed, it is sometimes to be remarked in this kind of variation, + that the variety belongs, strictly speaking, to neither of the immediate + parents; you will see a child in a family who is not like either its + father or its mother; but some old person who knew its grandfather or + grandmother, or, it may be, an uncle, or, perhaps, even a more distant + relative, will see a great similarity between the child and one of these. + In this way it constantly happens that the characteristic of some previous + member of the family comes out and is reproduced and recognised in the + most unexpected manner. + </p> + <p> + But apart from that matter of general experience, there are some cases + which put that curious mixture in a very clear light. You are aware that + the offspring of the Ass and the Horse, or rather of the he-Ass and the + Mare, is what is called a Mule; and, on the other hand, the offspring of + the Stallion and the she-Ass is what is called a 'Hinny'. I never saw one + myself; but they have been very carefully studied. Now, the curious thing + is this, that although you have the same elements in the experiment in + each case, the offspring is entirely different in character, according as + the male influence comes from the Ass or the Horse. Where the Ass is the + male, as in the case of the Mule, you find that the head is like that of + the Ass, that the ears are long, the tail is tufted at the end, the feet + are small, and the voice is an unmistakable bray; these are all points of + similarity to the Ass; but, on the other hand, the barrel of the body and + the cut of the neck are much more like those of the Mare. Then, if you + look at the Hinny,—the result of the union of the Stallion and the + she-Ass, then you find it is the Horse that has the predominance; that the + head is more like that of the Horse, the ears are shorter, the legs + coarser, and the type is altogether altered; while the voice, instead of + being a bray, is the ordinary neigh of the Horse. Here, you see, is a most + curious thing: you take exactly the same elements, Ass and Horse, but you + combine the sexes in a different manner, and the result is modified + accordingly. You have in this case, however, a result which is not general + and universal—there is usually an important preponderance, but not + always on the same side. + </p> + <p> + Here, then, is one intelligible, and, perhaps, necessary cause of + variation: the fact, that there are two sexes sharing in the production of + the offspring, and that the share taken by each is different and variable, + not only for each combination, but also for different members of the same + family. + </p> + <p> + 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 + organizations, 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. + </p> + <p> + 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. Reaumur, 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. + </p> + <p> + 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. + </p> + <p> + 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 Andre; 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. + </p> + <p> + 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, Andre, 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. + </p> + <p> + Now observe what very extraordinary phenomena are presented here. You have + an accidental variation arising from what you may call a monstrosity; you + have that monstrosity tendency 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 + Andre, who escaped in the first instance, escape altogether. + </p> + <p> + 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 + carried 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? Reaumur 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. + </p> + <p> + 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 trespass or 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Among ourselves this is well known. The simplest physical peculiarity is + mostly reproduced. I know a case of a man whose wife 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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 the large diagrams 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. + </p> + <p> + The third kind I mentioned—the Fantail—is 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. + </p> + <p> + 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 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 head and beak. + 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. + </p> + <p> + 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. + </p> + <p> + 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 organization 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; <a href="#linknote-1" name="linknoteref-1" + id="linknoteref-1"><small>1</small></a> 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. + </p> + <p> + 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. + </p> + <p> + <a name="linknote-1" id="linknote-1"> + <!-- Note --></a> + </p> + <p class="foot"> + 1 (<a href="#linknoteref-1">return</a>)<br /> [ 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.] + </p> + <p> + <br /><br /><br /><br /> + </p> +<pre xml:space="preserve"> + + + + + +End of the Project Gutenberg EBook of The Perpetuation Of Living Beings, +Hereditary Transmission And Variation, by Thomas H. Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK HEREDITARY TRANSMISSION *** + +***** This file should be named 2924-h.htm or 2924-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/9/2/2924/ + +Produced by Amy E. 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