"Meristic", "Homeotic", and "Substantive": a caveat
A "variation" was an observed characteristic of an organism (hence the organism was called a "variant"). Bateson considered there was a fundamental distinction between variations that affect the number or arrangement of body parts, which he deemed "meristic" (Greek: meros = part) and "homeotic" variations, respectively, and other variations, which he deemed "substantive". In his monumental Materials for the Study of Variation (1894) he introduced new terminology that is used to this day. Thus, a variant with an extra finger would be a meristic variant. A variant with a leg where an arm should be would be a homeotic variant. A variant with loss of normal colouration (e.g. an albino) would be a substantive variant.
It was difficult for him to imagine that meristic and homeotic variations could have originated in the same way as substantive variations.
We now know that some mutations happen to result in meristic variations. Some mutations happen to result in homeotic variations. Some mutations happen to result in substantive variations. It is true that there are different types of mutation (changes in DNA), but a given mutation (e.g. a base change from T to G) does not usually correspond to a particular type of variation. Bateson's thinking on substantive variation is presented with less handwaving than his thinking on the other variation types. Note that in the literature a mutation at the DNA level, and the observed result of that mutation (a "variant" or "mutant" organism), may both be called "a mutation," so the word must be understood in context.
Some Phenomenon of Arrangement
In Problems in Genetics (1913) Bateson states (p. 86):
"Of the way in which variations in the substantive composition of organisms are caused we have ... little real evidence, but we are beginning to know in what such variations must consist. These changes must occur either by the addition or loss of factors [to/from the gametes and hence to/from the progeny formed by those gametes]. We must not lose sight of the fact that, though the factors operate by the production of:
yet these bodies themselves [all three of the above] can scarcely themselves be genetic factors, but consequences of their existence.
That power is now a definite possession of the breed, present in all its germ-cells, male and female, taking part in their symmetrical divisions, and passed on equally to all, as much as [is passed on] the protoplasm or any other attribute of the breed." [Italics and numbers by DRF]
Although, as far as I am aware, Bateson never implied a factor to convey "information for", but only to convey the "power to cause" enzymes, substrates and enzyme-cofactors to appear in the offspring, in the following and other addresses he demonstrated the sense:
Maybe we should interpret "power to cause" as showing that Bateson understood the information concept, although he never used the word in this context (he used the word in other contexts)? Maybe he understood that different arrangements can convey different pieces of information. Judge for yourself when reading the paper below.
In the same sense, perhaps, Talmage proposed the clonal selection theory of immunity in 1957, without using the word "clonal". Burnet used the clonal "buzz-word" a year later. These days most commentators refer to "Burnet's clonal selection theory" (Click Here).
Some modern commentators assign the gene- as- information idea (Click Here) to Schrödinger in his What is Life? (CUP 1944). Certainly Darwin had the pangen- as- information idea (Click Here). Bateson may have got the "phenomenon- of- arrangement" idea from Weismann. In An Examination of Weismannism (1893, p. 182) Romanes states:
"But the theory of Pangenesis [of Darwin] does not suppose the future organism to exist in the egg-cell as a miniature (Romanes' italics): it supposes merely that every part of the future organism is represented in the egg-cell by corresponding material particles. And this, as far as I can understand, is exactly what the theory of germ-plasm [of Weismann] supposes; only it calls the particles 'molecules,' and seemingly attaches more importance to the matter of variations in their arrangement or 'constitution,' whatever these vague expressions may be intended to signify."
|Similarly, in Materials for the Study of Variation
Treated with Expecial Regard to Discontinuity in the Origin of Species
(1894), Bateson states:
"The body of one individual has never been the body of its parent," instead "the new body is made again new from the beginning just as if the wax model had gone back to the melting pot before the new model began."
Bateson regarded Samual Butler as "the most brilliant, and by far the most interesting of Darwin's opponents." In his book Luck or Cunning (1887), while not using the word "information," Butler showed a good understanding of the information concept (p. 260):
"As this idea [of a thing] is not like the thing itself, neither is it like the motions in our brain on which it is attendant. It is no more like these than, say, a stone is like the individual characters, written or spoken, that form the word 'stone' .....The shifting nature ... of our ideas and conceptions is enough to show that they must be symbolic and conditioned by changes going on within ourselves as much as those outside us."
Butler notes (p. 51) that "Variations, whether produced functionally [Lamarkism ] or not, can only be perpetuated and accumulated because they can be inherited." Throughout the book he emphases "the substantial identity between heredity and memory" a concept he attributes to the physiologist-psychologist Hering (1870).
According to Richard Goldschmidt, Hering's linkage of heredity and memory inspired Richard Semon who wrote two books on the theory of the "mneme," proposing that memory was "the consequence of an accumulation of mnemetic engrams produced by environmental action," which can compete for neural space (Portraits from Memory. Recollections of a Zoologist. 1956. Univ. Wash. Press, Seattle). Richard Dawkins was unaware of this when he suggested the word "meme," which could be "thought of as relating to memory" and is defined (OED) as "a self-replicating element of culture, passed on by imitation" (A Devil's Chaplain. 2003. Houghton Mifflin, Boston).
For Darwin's concept of information in 1868 (Click Here)
HEREDITY Nature, August 20th 1914
[On August 14th Great Britain declared war on Germany. Bateson's eldest son, John, was to be killed in 1918. Another son, Martin, enlisted in 1918, although inclined to conscientious objection; he committed suicide in 1922. His third son, Gregory, was too young to go to the war, and became an anthropologist/psychologist.]
THE AUSTRALIAN MEETING OF THE BRITISH ASSOCIATION
Inaugural Address by Prof. William Bateson, M.A., F.R.S., President
[Layout, illustrations and comments in square
brackets by DRF.]
The outstanding feature of this meeting must be the fact that we are here -- in Australia. It is the function of a president to tell the association of advances in science, to speak of the universal rather than of the particular or the temporary. There will be other opportunities of expressing the thoughts which this event must excite in the dullest heart, but it is right that my first words should take account of those achievements of organisation and those acts of national generosity by which it has come to pass that we are assembled in this country. Let us, too, on this occasion, remember that all the effort and all the goodwill that binds Australia to Britain, would have been powerless to bring about such a result had it not been for those advances in science which have given man a control of the forces of nature. For we are here by virtue of the feats of genius of individual men of science, giant-variations from the common level of our species; and since I am going soon to speak of the significance of individual variation, I cannot introduce that subject better than by calling to remembrance the line of pioneers in chemistry, in physics, and in engineering, by the working of whose rare -- or, if you will, abnormal -- intellects a meeting of the British Association on this side of the globe has been made physically possible.
I have next to refer to the loss within the year of Sir David Gill, a former president of this association, himself one of the outstanding great. His greatness lay in the power of making big foundations. He built up the Cape Observatory; he organised international geodesy; he conceived and carried through the plans for the photography of the whole sky, a work in which Australia is bearing a conspicuous part. Astronomical observation is now organised on an international scale, and of this great scheme Gill was the heart and soul. His labours have ensured a base from which others will proceed to discovery otherwise impossible. His name will be long remembered with veneration and gratitude.
As the subject of the addresses which I am to deliver here and in Sydney I take heredity. I shall attempt to give the essence of the discoveries made by Mendelian or analytical methods of study, and I shall ask you to contemplate the deductions which these physiological facts suggest in application both to the evolutionary theory at large and to the special case of the natural history of human society.
Recognition of the significance of heredity is modern. The term itself in its scientific sense is no older than Herbert Spencer. Animals and plants are formed as pieces of living material split from the body of the parent organisms. Their powers and faculties are fixed in their physiological origin. They are the consequence of a genetic process, and yet it is only lately that this genetic process has become the subject of systematic research and experiment.
The curiosity of naturalists has of course always been
attracted to such problems; but that accurate knowledge of genetics is of paramount
importance in any attempt to understand the nature of living things has only been realised
quite lately even by naturalists, and with casual exceptions the laity still know nothing
of the matter. Historians debate the past of the human species, and statesmen order its
present or profess to guide its future as if the animal man, the unit of their
calculations, with his vast diversity of powers, were a homogeneous material, which can be
multiplied like shot.
The first full perception of the significance of variation we owe to Darwin. The present generation of evolutionists realises perhaps more fully than did the scientific world in the last century that the theory of evolution had occupied the thoughts of many, and found acceptance with not a few, before ever the "Origin" appeared.
We have come also to the conviction that the principle of natural selection cannot have been the chief factor in delimiting the species of animals and plants, such as we now, with fuller knowledge, see them actually to be. We are even more sceptical as to the validity of that appeal to changes in the conditions of life as direct causes of modification, upon which latterly at all events Darwin laid much emphasis. But that he was the first to provide a body of fact demonstrating the variability of living things, whatever be its causation, can never be questioned.
There are some older collections of evidence, chiefly the work of the French
school, especially of Godron (1)--and I would mention also the almost
forgotten essay of Wollaston (2) -- these, however, are only fragments in
comparison. Darwin regarded variability as a property
inherent in living things, and eventually we must consider whether this
conception is well founded; but postponing that inquiry for the present, we may declare
that with him began a general recognition of variation as a phenomenon widely occurring in
The chromosomes of nearly related creatures may be utterly different both in number, size, and form.Only one piece of evidence encourages the old hope that a connection might be traceable between the visible characteristics of the body and those of the chromosomes. I refer, of course, to the accessory chromosome [X chromosome], which in many animals distinguishes the spermatozoon about to form a female in fertilisation [from the spermatozoon about to form a male in fertilization].
Even it, however, cannot be claimed as the cause of sexual differentiation, for it may be paired in forms closely allied to those in which it is unpaired or accessory. The distinction may be present [positive] or wanting [negative], like any other secondary sexual character. Indeed, so long as no one can show consistent distinctions between the cytological characters of somatic tissues [i.e. differences in chromosome morphology] in the same individual, we can scarcely expect to perceive such distinctions between the chromosomes of the various types [of organism].
For these methods of attack we now substitute another, less ambitious, perhaps, because less comprehensive, but not less direct. If we cannot see how a fowl by its egg and its sperm gives rise to a chicken, or how a sweet pea from its ovule and its pollen grain produces another sweet pea, we at least can watch the system by which the differences between the various kinds of fowls or between the various kinds of sweet peas are distributed among the offspring. By thus breaking the main problem up into its parts we give ourselves fresh chances.
This analytical study we call Mendelian because Mendel was the first
to apply it. To be sure, he did not approach the problem by any such line of reasoning as
I have sketched. His object was to determine the genetic
definiteness of species; but though in his writings he makes no mention of
inheritance, it is clear that he had the extension in view. By cross-breeding he combined
the characters of varieties in mongrel individuals [hybrids],
and set himself to see how these characters would be distributed among the individuals of
subsequent generations. Until he began this analysis nothing but the vaguest answers to
such a question had been attempted. The existence of any orderly system of descent was
never even suspected. In their manifold complexity human characteristics seemed to follow
no obvious system, and the fact was taken as a fair sample of the working of heredity.
Truer notions of genetic physiology are given by the Hebrew
expression "seed". If we speak of a man as "of the blood-royal" we think at once of plebeian dilution, and
we wonder how much of the royal fluid is likely to be "in his
veins"; but if we say he is "of the seed of Abraham"
we feel something of the permanence and indestructibility of that germ which can be
divided and scattered among all nations, but remains recognisable in type and
characteristics after 4000 years.
The allotment of characteristics among offspring is not accomplished by the exudation of drops of a tincture representing the sum of the characteristics of the parent organism, but by a process of cell-division, in which numbers of these characters, or rather the elements upon which they depend, are sorted out among the resulting germ-cells in an orderly fashion. .
What these elements, or factors as we call them, are we do not know. That they are in some way directly transmitted by the material of the ovum and of the spermatozoon is obvious, but it seems to me unlikely that they are in any simple or literal sense material particles. I suspect rather that their properties depend on some phenomenon of arrangement [? sequence or code].
However that may be, analytical breeding [breeding which allows us to deduce the genotype of the parents from the phenotype of offspring] proves that it is according to the distribution of these genetic factors, to use a non-committal term, that the [observable] characters of the offspring are decided. The first business of experimental genetics is to determine their number and interactions, and then to make an analysis of the various types of life.
Now the ordinary genealogical trees, such as those which the studbooks provide in the case of the domestic animals, or the Heralds' College provides in the case of man, tell nothing of all this. Such methods of depicting descent cannot even show the one thing they are devised to show -- purity of "blood". For at last we know the physiological meaning of that expression. An organism is pure-bred when it has been formed by the union in fertilisation of two germ-cells which are alike in the factors they bear; and since the factors for the several characteristics are independent of each other, this question of purity must be separately considered for each of them.
A man, for example, may be pure-bred in respect of his musical ability and cross-bred in respect of the colour of his eyes or the shape of his mouth. Though we know nothing of the essential nature of these factors, we know a good deal of their powers. They may confer height, colour, shape, instincts, powers both of mind and body; indeed, so many of the attributes which animals and plants possess that we feel justified in the expectation that, with continued analysis, they will be proved to be responsible for most if not all the differences by which the varying individuals of any species are distinguished [phenotypically] from each other. I will not assert that the greater differences which characterise [are used to describe] distinct species are due generally to such independent factors, but that is the conclusion to which the available evidence points. All this is now so well understood, and has been so often demonstrated and expounded, that details of evidence are now superfluous.
But for the benefit of those who are unfamiliar with such work let me briefly epitomise its main features and consequences. Since genetic factors are definite things, either present in or absent from any germ-cell [gamete], the individual [resulting from the union of gametes] may be either "pure-bred" for any particular factor, or ["pure-bred" for] its absence, if he is constituted by the union of two germ-cells [either] both possessing, or both destitute of, the factor. If the individual is thus pure, all his germ-cells will in that respect be identical, for they are simply bits of the similar germ-cells which united in fertilisation to produce the parent organism.
We thus reach the essential principle, that an organism cannot pass
on to the offspring a factor which it did not itself receive in fertilisation. Parents,
therefore, which are both destitute of a given factor can only produce offspring equally
destitute of it; and, on the contrary, parents both pure-bred for the presence of a factor
produce offspring equally purebred for its presence. Whereas the germ-cells of the
pure-bred are all alike, those of the cross-bred, which results from the union of
dissimilar germ-cells, are mixed in character. Each positive factor segregates from its
negative opposite, so that some germ-cells carry the factor and some do not. Once the
factors have been identified by their effects, the average composition of the several
kinds of families formed from the various matings can be predicted.
The question is often asked whether there are not also in operation systems of descent quite other than those contemplated by the Mendelian rules. I myself have expected such discoveries, but hitherto none have been plainly demonstrated.
It is true we are often puzzled by the failure of a parental type to reappear in its completeness after a cross -- the merino sheep or the fantail pigeon, for example. These exceptions may still be plausibly ascribed to the interference of a multitude of factors, a suggestion not easy to disprove; though it seems to me equally likely that segregation has been in reality imperfect.
Of the descent of quantitative characters we still know practically nothing. These and hosts of difficult cases remain almost untouched. In particular the discovery of E. Baur, and the evidence of Winkler in regard to his "graft hybrids," both showing that the sub-epidermal layer of a plant -- the layer from which the germ-cells are derived -- may bear exclusively the characters of a part only of the soma, give hints of curious complications, and suggest that in plants at least the interrelations between soma and gamete may be far less simple than we have supposed.
Nevertheless, speaking generally, we see nothing to indicate that qualitative characters descend, whether in plants or animals, according to systems which are incapable of factorial representation.
The body of evidence accumulated by this method of analysis is now very large, and is still growing fast by the labours of many workers. Progress is also beginning along many novel and curious lines. The details are too technical for inclusion here. Suffice it to say that not only have we proof that segregation affects a vast range of characteristics, but in the course of our analysis phenomena of most unexpected kinds have been encountered. Some of these things twenty years ago must have seemed inconceivable.
For example, the two sets of sex organs, male and female, of
the same plant may not be carrying the same characteristics; in some animals
characteristics, quite independent of sex, may be distributed solely or predominantly to
one sex; in certain species the male may be breeding true to its own type, while the
female is permanently mongrel, throwing off eggs of a distinct variety in addition to
those of its own type; characteristics, essentially independent, may be associated in
special combinations which are largely retained in the next generation, so that among the
grandchildren there is numerical preponderance of those combinations which existed in the
grandparents -- a discovery [linkage]
which introduces us to a new phenomenon of polarity in the
It is obvious that such discoveries have bearings on most of the problems, whether theoretical or practical, in which animals and plants are concerned. Permanence or change of type, perfection of type, purity or mixture of race, "racial development," the succession of forms, from being vague phrases expressing matters of degree, are now seen to be capable of acquiring physiological meanings, already to some extent assigned with precision.
For the naturalist -- and it is to him that I am especially addressing myself to-day -- these things are chiefly significant as relating to the history of organic beings -- the theory of evolution, to use our modern name. They have, as I shall endeavour to show in my second address to be given in Sydney, an immediate reference to the conduct of human society.
I suppose that everyone is familiar in outline with the theory of the
origin of species which Darwin promulgated. Through the last fifty years this theme of the
Natural Selection of favoured races has been developed and expounded in writings
innumerable. Favoured races certainly can replace others. The argument is sound, but we
are doubtful of its value. For us that debate stands adjourned. We go to Darwin for his
incomparable collection of facts. We would fain emulate his scholarship, his width and his
power of exposition, but to us he speaks no more with philosophical authority. We read his
scheme of evolution as we would those of Lucretius or of Lamarck, delighting in their
simplicity and their courage. The practical and experimental study of variation and
heredity has not merely opened a new field; it has given a new point of view and new
standards of criticism. Naturalists may still be found expounding teleological systems
(4) which would have delighted Dr. Pangloss himself, but at the present time few
are misled. The student of genetics knows that the time for
the development of theory is not yet. He would rather stick to the seed-pan and the
Shorn of these pretensions,
doctrine of the survival of favoured races is a truism, helping scarcely at all to account
for the diversity of species. Tolerance plays almost as considerable a
part. By these admissions almost the last shred of that teleological fustian with which
Victorian philosophy loved to clothe the theory of evolution is destroyed. Those who would
proclaim that whatever is, is right, will be wise henceforth to base this faith frankly on
the impregnable rock of superstition and to abstain from direct appeals to natural fact.
Every theory of evolution must be such as to accord with the facts of physics and
chemistry, a primary necessity to which our predecessors paid small heed. For them the
unknown was a rich mine of possibilities on which they could freely draw. For us it is
rather an impenetrable mountain out of which the truth can be chipped in rare and isolated
fragments. Of the physics and chemistry of life we know next to
nothing. Somehow the characters of living things are bound up in properties
of colloids, and are largely determined by the chemical powers of enzymes,
but the study of these classes of matter have only just begun. Living things are found by
a simple experiment to have powers undreamt of, and who knows what may be behind?
Variation is postulated as the basis of all evolutionary change. Do we then as a matter of fact find in the world about us variations occurring of such a kind as to warrant faith in a contemporary progressive evolution? Till lately most of us would have said "yes" without misgiving. We should have pointed, as Darwin did, to the immense range of diversity seen in many wild species, so commonly that the difficulty is to define the types themselves.
Still more conclusive seemed the profusion of forms in the various domesticated animals and plants, most of them incapable of existing even for a generation in the wild state, and therefore fixed unquestionably by human selection. These, at least, for certain, are new forms, often distinct enough to pass for species, which have arisen by variation.
But when analysis is applied to this mass of variation the matter wears a different aspect. Closely examined, what is the "variability" of wild species? What is the natural fact which is denoted by the statement that a given species exhibits much variation? Generally one of two things: either that the individuals collected in one locality differ among themselves; or perhaps more often that samples from separate localities differ from each other. As direct evidence of variation it is clearly to the first of these phenomena that we must have recourse -- the heterogeneity of a population breeding together in one area.
Thus heterogeneity may be in any degree, ranging from slight differences that systematists would disregard, to a complex variability such as we find in some moths, where there is an abundance of varieties so distinct that many would be classified as specific forms, but for the fact that all are freely breeding together.
Naturalists formerly supposed that any of
these varieties might be bred from any of the others. Just as the reader of novels is
prepared to find that any kind of parents might have any kind of children in the course of
the story, so was the evolutionist ready to believe that any pair of moths might produce
any of the varieties included in the species. Genetic analysis has disposed of all these
mistakes. We have no longer the smallest doubt that in all
these examples the varieties stand in a regular descending order, and that they are simply
terms in a series of combinations of factors separately transmitted, of which each may be
present or absent.
We are left with a picture of variation utterly different from that which we saw at first. Variation now stands out as a definite physiological event. We have done with the notion that Darwin came latterly to favour, that large differences can arise by accumulation of small differences. Such small differences are often mere ephemeral effects of conditions of life, and as such are not transmissible; but even small differences, when truly genetic, are factorial like the larger ones, and there is not the slightest reason [at the time Bateson was speaking] for supposing that they are capable of summation.
As to the origin or source of these
separable factors, we are without any indication or surmise.
effects we know them to be definite, as
definite, say, as the organisms which produce disease; but how they arise and how they
come to take part in the composition of the living creature so that when present they are
treated in cell-division as constituents of the germs, we cannot conjecture.
To be sure, there are breeds, such as black-red game and brown leghorns, which have the colours of the jungle-fowl, though they differ in shape and other respects. As we know so little as yet of the genetics of shape, let us assume that those transitions could be got over. Suppose, further, as is probable, that the absence of the maternal instinct in the leghorn is due to loss of one factor which the jungle-fowl possesses. So far we are on fairly safe ground. But how about white leghorns? Their origin may seem easy to imagine, since white varieties have often arisen in well-authenticated cases.
But the white of white leghorns is not, as white in nature often is, due to the loss of the colour-elements, but to the action of something which inhibits their expression. Whence did that something come? The same question may be asked respecting the heavy breeds, such as Malays or Indian game. Each of these is a separate introduction from the East. To suppose that these, with their peculiar combs and close feathering, could have been developed from pre-existing European breeds is very difficult. On the other hand, there is no wild species now living any more like them.
We may, of course, postulate that there was once such a species, now lost. That is quite conceivable, though the suggestion is purely speculative. I might thus go through the list of domesticated animals and plants of ancient origin and again and again we should be driven to this suggestion, that many of their distinctive characters must have been derived from some wild original now lost. Indeed, to this unsatisfying conclusion almost every careful writer on such subjects is now reduced.
I f we turn to modern evidence the case looks even worse. The new breeds of domestic animals made in recent times are the carefully selected products of recombination of pre-existing breeds. Most of the new varieties of cultivated plants are the outcome of deliberate crossing. There is generally no doubt in the matter. We have pretty full histories of these crosses in gladiolus, orchids, cineraria, begonia, calceolaria, pelargonium, etc. A very few certainly arise from a single origin. The sweet pea is the clearest case, and there others which I should name with hesitation.
The cyclamen is one of them, but we know that efforts to cross cyclamens were made early in the cultural history of the plant, and they may very well have been successful. Several plants for which single origins are alleged, such as the Chinese primrose, the dahlia, and tobacco, came to us in an already domesticated state, and their origins remain altogether mysterious. Formerly single origins were generally presumed, but at the present time numbers of the chief products of domestication, -- dogs, horses, cattle, sheep, poultry, wheat, oats, rice, plums, cherries, -- have in turn been accepted as "polyphyletic" or, in other words, derived from several distinct forms.
The reason that has led to these judgments is that the distinctions
between the chief varieties can be traced as far back as the evidence reaches, and that
these distinctions are so great, so far transcending anything that we actually know
variation capable of effecting, that it seems pleasanter to postpone the difficulty,
relegating the critical differentiation to some misty antiquity into which we shall not be
asked to penetrate. For it need scarcely be said that this is mere procrastination. If the
origin of a form under domestication is hard to imagine, it becomes no easier to conceive
of such enormous deviation from type coming to pass in the wild state. Examine any two
thoroughly distinct species which meet each other in their distribution, as, for instance,
Lychnis diurna and vespertina do [red and
white campions]. In areas of overlap are many intermediate forms. These
used to be taken to be transitional steps, and the specific distinctness of vespertina and
diurna was on that account questioned. Once it is known that
these supposed intergrades are merely mongrels between the two species the transition from
one to the other is practically beyond our powers of imagination to conceive. If both
these can survive, why has their common parent perished? Why when they cross do they not
reconstruct it instead of producing partially sterile hybrids? I take this
example to show how entirely the facts were formerly misinterpreted.
varieties -- for instance, of Chinese Primula -- each breeding true, and in the second generation by mere recombination of the various factors which the two parental types severally introduced, there will be a profusion of forms, utterly unlike each other, distinct also from the original parents. Many of these can be bred true, and if found wild would certainly be described as good species.
Confronted by the difficulty I have put before you, and contemplating such amazing polymorphism in the second generation from a cross in Antirrhinum, Lotsy has lately with great courage suggested to us that all variation may be due to such crossing. I do not disguise my sympathy with this effort. After the blind complacency of conventional acknowledgement of the hardness of the problem, Lotsy's utterance will at least do something to expose the artificiality of systematic zoology and botany. Whatever might or might not be revealed by experimental breeding, it is certain that without such tests we are merely guessing when we profess to distinguish specific limits and to declare that this is a species and that a variety. The only definable unit in classification is the homozygous form which breeds true. When we presume to say that such and such differences are trivial and such others valid, we are commonly embarking on a course for which there is no physiological warrant.
Who could have foreseen that the apple and the pear -- so like each other that their botanical differences are evasive -- could not be crossed together, though species of Antirrhinum so totally
unlike each other as majus and molle can be
hybridised, as Baur has
shown, without a sign of impaired fertility? Jordan was perfectly right. The true-breeding
forms which he distinguished in such multitudes are real entities, though the great
systematists, dispensing with such laborious analysis, have pooled them into arbitrary
Linnean species, for the convenience of collectors and for the simplification of
catalogues. Such pragmatical considerations may mean much in the museum, but with them the
student of the physiology of variation has nothing to do. These "little species," finely cut, true-breeding, and innumerable
mongrels between them are what he finds when he examines any so-called variable type. On
analysis the semblance of variability disappears, and the illusion is shown to be fixed.
In face of such a result we may well ask with Lotsy, is there such a thing as spontaneous
variation anywhere? His answer is that there is not.
Then again in regard to those variations in number and division of parts which we call meristic, the reference of these to original cross-breeding is surely barred by the circumstances in which they often occur. There remain also the rare examples mentioned already in which a single wild origin may with much confidence be assumed. In spite of repeated trials, no one has yet succeeded in crossing the Sweet Pea with any other leguminous species. We know that early in its cultivated history it produced at least two marked varieties which I can only conceive of as spontaneously arising, though, no doubt, the profusion of forms we now have was made by the crossing of those original varieties.
I mention the Sweet Pea thus prominently for another reason, that it
introduces us to another though subsidiary form of variation, which may be described as a fractionation of factors. Some of my Mendelian
colleagues have spoken of genetic factors as permanent and indestructible. Relative
permanence in a sense they have, for they commonly come out unchanged after segregation.
But I am satisfied that they may occasionally undergo a quantitative disintegration, with
the consequence that varieties are produced intermediate between the integral varieties
from which they were derived. These disintegrated conditions I have spoken of as
subtraction -- or reduction -- stages. For example, the Picotee Sweet Pea, with its purple
edges, can surely be nothing but a condition produced by the factor which ordinarily makes
the fully purple flower, quantitatively diminished. The pied animal, such as the Dutch
rabbit, must similarly be regarded as the result of partial defect of the chromogen from
which the pigment is formed, or conceivably of the factor which effects its oxidation. On
such lines I think we may with great confidence interpret all those intergrading forms
which breed true and are not produced by factorial interference.
In passing let us note how the history of the sweet pea belies those
ideas of a continuous evolution with which we had formerly to contend. The big varieties
came first. The little ones have arisen later, as I suggest, by fractionation. Presented
with a collection of modern sweet peas how prettily would the devotees of continuity have
arranged them in a graduated series, showing how every intergrade could be found, passing
from the full colour of the wild Sicilian species in one direction to white, in the other
to the deep purple of "Black Prince," though happily we know these two to be
among the earliest to have appeared.
When the facts of genetic discovery become familiarly known to biologists, and cease to be the preoccupation of a few, as they still are, many and long discussions must inevitably arise on the question, and I offer these remarks to prepare the ground. I ask you simply to open your minds to this possibility. It involves a certain effort. We have to reverse our habitual modes of thought. At first it may seem rank absurdity to suppose that the primordial form or forms of protoplasm could have contained complexity enough to produce the divers types of life. But is it easier to imagine that these could have been conveyed by extrinsic additions? Of what nature could these additions be? Additions of material cannot surely be in question. We are told that salts of iron in the soil may turn a pink hydrangea blue. The iron cannot be passed on the the next generation. How can the iron multiply itself? The power to assimilate the iron is all that can be transmitted.
A disease-producing organism like the pebrine of silkworms can in a very few cases be passed on through the germ-cells. Such an organism can multiply and can produce its characteristic effects in the next generation. But it does not become part of the invaded host, and we cannot conceive it taking part in the geometrically ordered processes of segregation. These illustrations may seem too gross; but what refinement will meet the requirements of the problem, that the thing introduced must be, as the living organism itself is, capable of multiplication and of subordinating itself in a definite system of segregation?
That which is conferred in variation must rather itself be a change, not of material, but of arrangement [? sequence], or of motion. The invocation of additions extrinsic to the organism does not seriously help us to imagine how the power to change can be conferred, and if it proves that hope in that direction must be abandoned, I think we lose very little. By the re-arrangement of a very moderate number of things we soon reach a number of possibilities practically infinite. That primordial life may have been of small dimensions need not disturb us. Quantity is of no account in these considerations. Shakespeare once existed as a speck of protoplasm not so big as a small pin's head. To this nothing was added that would not equally well have served to build up a baboon or a rat.
Let us consider how far we can get by the process of removal of what we call "epistatic" factors, in other words those that control, mask, or suppress underlying powers and faculties. I have spoken of the vast range of colours exhibited by modern sweet peas. There is no question that these have been derived from the one wild bi-colour form by a process of successive removals. When the vast range of form, size, and flavour to be found among the cultivated apples is considered it seems difficult to suppose that all this variety is hidden in the wild crab-apple. I cannot positively assert that this is so, but I think all familiar with Mendelian analysis would agree with me that it is probable, and that the wild crab contains presumably inhibiting elements which the cultivated kinds have lost. The legend that the seedlings of cultivated apples become crabs is often repeated. After many inquiries among the raisers of apple seedlings I have never found an authentic case -- once only even an alleged case, and this on inquiry proved to be unfounded.
I have confidence that the artistic gifts of mankind will prove to be due not to something added to the make-up of an ordinary man, but to the absence of factors which in the normal person inhibit the development of these gifts. They are almost beyond doubt to be looked upon as releases of powers normally suppressed. The instrument is flowers or fruits, the finely repeated divisions that give its quality to the wool of the merino, or in an analogous case the multiplicity of quills to the tail of the fantail pigeon, are in all probability other examples of such releases.
You may ask what guides one in the discrimination of the positive factors and how we can satisfy ourselves that the appearance of a quality is due to loss. It must be conceded that in these determinations we have as yet recourse only to the effects of dominance. When the tall pea is crossed with the dwarf, since the offspring is tall we say that the tall parent passed a factor into the cross-bred which makes it tall. The pure tall parent had two doses of this factor; the dwarf had none; and since the cross-bred is tall we say that one dose of the dominant tallness is enough to give the full height. The reasoning seems unanswerable.
But the commoner result of crossing is the production of a form intermediate between the two pure parental types. In such examples we see clearly enough that the full parental characteristics can only appear when they are homozygous -- formed from similar germ-cells, and that one dose is insufficient to produce either effect fully. When this is so we can never be sure which side is positive and which negative. Since, then, when dominance is incomplete we find ourselves in this difficulty, we perceive that the amount of the effect is our only criterion in distinguishing the positive from the negative, and when we return even to the example of the tall and dwarf peas the matter is not so certain as it seemed.
Professor Cockerell lately found among thousands of yellow sunflowers one which was partly red. By breeding he raised from this a form wholly red. Evidently the yellow and the wholly red are the pure forms, and the partially red is the heterozygote. We may then say that the yellow is YY with two doses of a positive factor which inhibits the development of pigment; the red is yy, with no dose of the inhibitor; and the partially red are Yy, with only one dose of it. But we might be tempted to think the red was a positive characteristic, and invert the expressions, representing the red as RR, the partly red as Rr, and the yellow as rr. According as we adopt the one or the other system of expression we shall interpret the evolutionary change as one of loss or as one of addition.
May we not interpret the other apparent new dominants in the
same way? The white dominant in the fowl or in the Chinese primula can inhibit
may it not be that the original coloured fowl or primula had two doses of a factor which
inhibited this inhibitor? The Petter moth, Amphidasys betularia, produced in
England about 1840 a black variety, then a novelty, now common in certain areas, which
behaves as a full dominant. The pure blacks are no blacker than the cross-bred. Though at
first sight it seems that the black must have been something added, we can without
absurdity suggest that the normal is the term in which two doses of inhibitor are present,
and that in the absence of one of them the black appears.
We should be greatly helped by some indication as to
origin of life has been single or multiple. Modern opinion is, perhaps, inclining to the
multiple theory, but we have no real evidence. Indeed, the problem still stands outside
the range of scientific investigation, and when we hear the spontaneous formation of
formaldehyde mentioned as a possible first step in the origin of life, we think of Harry
Lauder in the character of a Glasgow schoolboy pulling out his treasures from his
pocket--"That's a wassher--for makkin' motor cars"!
Modern research lends not the smallest encouragement or sanction to the view that gradual evolution occurs by the transformation of masses of individuals, though that fancy has fixed itself on popular imagination. The isolated events to which variation is due are evidently changes in the germinal tissues, probably in the manner in which they divide.
It is likely that the occurrence of these variations is wholly irregular, and as to their causation [chemistry of mutation] we are absolutely without surmise or even plausible speculation. Distinct types [of organism] once arisen, no doubt a profusion of the forms called species have been derived from them by simple crossing and subsequent recombination. New species may be now in course of creation by this means, but the limits of the process are obviously narrow.
On the other hand, we see no changes in progress around us in the contemporary world which we can imagine likely to culminate in the evolution of forms distinct in the larger sense. By intercrossing dogs, jackals, and wolves new forms of these types can be made, some of which may be species, but I see no reason to think that from such material a fox could be bred in indefinite time, or that dogs could be bred from foxes.
Whether science will hereafter discover that certain groups can by peculiarities in their genetic physiology be declared to have a prerogative quality justifying their recognition as species in the old sense, and that the differences of others are of such a subordinate degree that they may in contrast be termed varieties, further genetic research alone can show. I myself anticipate that such a discovery will be made, but I cannot defend the opinion with positive conviction.
Somewhat reluctantly, and rather from a sense of duty, I have devoted
most of this address to the evolutionary aspects of genetic research. We cannot keep these
things out of our heads, though sometimes we wish we could. The outcome, as you will have
seen, is negative, destroying much that till lately passed for gospel. Destruction may be
useful, but it is a low kind of work. We are just about where Boyle was in the seventeenth
century. We can dispose of alchemy, but we cannot make more than a quasi-chemistry. We are
awaiting our Priestley and our Mendeléeff. In truth it is not these wider aspects of
genetics that are at present our chief concern. They will come in their time. The great
advances of science are made like those of evolution, not by imperceptible
mass-improvement, but by the sporadic birth of penetrative genius. The journeymen follow
after him, widening and clearing up, as we are doing along the track that Mendel found.
differences were held to be changes in chromosome "pattern,"
and "within species, the
internal chromosome pattern may slowly change in a series of steps
without any visible effect on the phenotype and without any
accumulation of so-called gene mutations, small or large!"
"within species, the internal chromosome pattern may slowly change in a series of steps without any visible effect on the phenotype and without any accumulation of so-called gene mutations, small or large!"
"The question now arises as to how a change of the serial pattern within the chromosomes can be conceived as having evolutionary significance. Only a few years ago such an idea would have had to be considered utterly senseless. The chromosome was the carrier of a string of genes, independent, atomistic units of at least molecular order, ... A genetic change could, therefore, be conceived of only as a change in one or more individual genes, - a mutation. Evolution in terms of chromosomes, therefore, could mean only accumulation of gene mutations, loss of existent genes, or creation of new genes.
This conception has actually become an article of faith, a credo which remains unshaken, when occasionally some critical mind tried to follow the idea to its ultimate conclusion, as did my predecessor in this lectureship, the great skeptic Bateson (1914). His shocking conclusions were accepted as a kind of grim joke, though he probably was very serious about carrying the genetic theory of his time to its inevitable consequences. ...
The classical theory of the gene and its mutations did not leave room for any other method of evolution. Certainly a pattern change within the serial structure of a chromosome, unaccompanied by gene mutation or loss, could have no effect whatsoever upon the hereditary type and therefore could have not significance for evolution. But now pattern changes are facts of such widespread and ... typical occurrence that we must take a definite stand regarding their significance... .
The intimate serial pattern of the chromosome is important for the action of the hereditary material. Chromosomal breaks which lead to new serial arrangements of the parts of chromosomes; namely, deficiencies, inversions, duplications, and translocations ... may produce definite genetic effects which are not different from the typical effects of mutations... .
Though many geneticists still cling to an explanation of these pattern effects in terms of gene neighbourhoods, it is becoming more and more evident that the effect has nothing to do with the theoretical units, the genes, but is an independent effect of the whole chromosome or of more or less small sections of it. The normal serial pattern has a definite genetic effect which is changed with a change in the pattern, and eventual units, such as genes have nothing whatsoever to do with the effect.
If we were to illustrate this conception with a simile, we might use one of the following models.
A repatterning of a chromosome may have exactly the same effect as an accumulation of mutations. And, even more so, a complete repatterning might produce a new chemical system ... This encourages me to believe that the dead end reached by neo-Darwinian theory based upon the conceptions of classical genetics can now be passed successfully." (ibid. pp. 200-205)
A systemic mutation (or series of such), then, consists of a change of intrachromosomal pattern... . Whatever genes or gene mutations might be, they do not enter this picture at all. Only the arrangement of the serial chemical constituents of the chromosomes into a new, spatially different order; i.e. a new chromosomal pattern, is involved. The new pattern seems to emerge slowly in a series of consecutive steps ... . These steps may be without a visible effect until the repatterning of the chromosome ... leads to a new stable pattern, that is, a new chemical system. This may have attained a threshold of action beyond which the physiological reaction system of development, controlled by the new genetic pattern, is so basically changed that a new phenotype emerges, the new species, separated from the old one by a bridgeless gap and an incompatible intrachromosomal pattern. 'Emergent evolution' but without mysticism! ...This viewpoint, cogent as it is, ... is to be understood only after the fetters of atomistic gene theory have been thrown off, a step which is unavoidable but which requires a certain elasticity of mind... ." (ibid. pp. 205-6)
"The term reaction system was introduced into genetics by Goodspeed and Clausen (1916), who realized at that early date ... that something more than the addiditive action of individual genes must be involved in genetic determination. It is highly significant that they derived their new concept from experiences with species hybrids. As a matter of fact, these authors did not take the decisive step away from the genetic mosaic conception, but they tried to expand it by adding the new idea of reaction system:
The plant which gives us tobacco appeared to Goldschmidt to be particularly informative:
The modern reader can here note that decades later it was found that the two sets of chromosomes differ in their base composition (GC%; Matassi et al. 1991. Nucleic Acids Res. 19, 5561-7). In "pattern" Goldschmidt was thinking, along the same lines as Bateson, in terms of "sequence."
Go to: Bateson & Saunders (1902) (Click Here)
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Last edited 07 Dec 2003 by Donald Forsdyke