Chapter VIII: Abbot Mendel: a New Outlook in Heredity 195 (6)

What will doubtless rank as one of the greatest discoveries in the
study of biology, and in the study of heredity, perhaps the
greatest, was made by Gregor Mendel, an Austrian monk, in the garden
of his cloister, some forty years ago. The discovery was announced
in the proceedings of a fairly well-known scientific society, but
seems to have attracted little attention, and to have been soon
forgotten. The Darwinian theory then occupied the centre of the
scientific stage, and Mendel's brilliant discovery was all but
unnoticed for a third of a century. Meanwhile, the discussion
aroused by Weissman's germ plasm theory, in particular the idea of
the non-inheritance of acquired characters, put the scientific
public into a more receptive frame of mind. Mendel's law was
rediscovered {199} independently by three different botanists,
engaged in the study of plant hybrids--de Vries, Correns, and
Tschermak, in the year 1900. It remained, however, for a zoologist,
Bateson, two years later, to point out the full importance and the
wide applicability of the law. Since then the Mendelian discoveries
have attracted the attention of biologists generally.
[Footnote 15]

[Footnote 15: This paper was originally published in part in the
_Proceedings of the American Academy of Arts and Sciences_, Vol.
xxxviii, No. 18, January, 1903. It may be found complete in
_Science_ for 25 September, 1903.]

Professor Bateson, whose book on Mendel's "Principles of Heredity" is the best popular exposition in English of Mendel's work, says that an exact determination of the laws of heredity will probably produce more change in man's outlook upon the world and in his power over nature than any other advance in natural knowledge that can be clearly foreseen. No one has better opportunities of pursuing such work than horticulturists and stockbreeders. They are daily witnesses of the phenomena of heredity. Their success also depends largely on a knowledge of its laws, and obviously every increase in that knowledge is of direct and special importance to them.

After thus insisting on the theoretic and practical importance of the subject, Professor Bateson says:--

As regards the Mendelian principles which it is the chief aim of
this introduction to present clearly before the reader, it may be
said that by the {200} application of those principles we are
enabled to reach and deal in a comprehensive manner with phenomena
of a fundamental nature, lying at the very root of all conceptions
not merely of the physiology of reproduction and heredity, but even
of the essential nature of living organisms; and I think that I use
no extravagant words when, in introducing Mendel's work to the
notice of the Royal Horticultural Society's Journal, I ventured to
declare that his experiments are worthy to rank with those which
laid the foundation of the atomic laws of chemistry.

Professor L. H. Bailey, who is the Director of the Horticultural Department at Cornell University and the editor of the authoritative _Encyclopedia of Horticulture_, was one of the first of recent scientists to call attention to Mendel's work. It was, we believe, because of a reference to Mendel's papers by Bailey that Professor de Vries was put on the track of Mendel's discoveries and found that the Austrian monk had completely anticipated the work at which he was then engaged. In a recent issue of _The Independent_, of New York, Professor Bailey said:--

The teaching of Mendel strikes at the root of two or three difficult
and vital problems. It presents a new conception of the proximate
mechanism of heredity. The hypothesis of heredity that it suggests
will focus our attention along new lines, and will, I believe,
arouse as much discussion as Weissmann's hypothesis, and it is
probable that it will have a wider influence. Whether it expresses
the actual means of heredity or not, it is yet much too early to
say. But the hypothesis (which Father Mendel evolved in order to
explain the reasons for his law as he saw them) is even a {201}
greater contribution to science than the so-called Mendel's Law as
to the numerical results of hybridization. In the general discussion
of evolution Mendel's work will be of the greatest value because it
introduces a new point of view, challenges old ideas and opinions,
gives us a new theory for discussion, emphasizes the great
importance of actual experiments for the solution of many questions
of evolution, and then forces the necessity for giving greater
attention to the real characters and attributes of plants and
animals than to the vague groups that we are in the habit of calling
species.

It is very evident that a man of whose work so many authorities are agreed that it is the beginning of a new era in biology, and especially in that most interesting of all questions, heredity, must be worthy of close acquaintance. Hence the present sketch of his career and personality, as far as they are ascertainable, for his modesty, and the failure of the world to recognize his worth in his lifetime, have unfortunately deprived us of many details that would have been precious.

Gregor Johann Mendel was born 27 July, 1822, at Heinzendorf, nor far from Odrau, in Austrian Silesia. He was the son of a well-to-do peasant farmer, who gave him every opportunity of getting a good education when he was young. He was educated at Olmutz, in Moravia, and after graduating from the college there, at the age of twenty-one, he entered as a novice the Augustinian Order, beginning his novitiate in 1843 in the Augustinian monastery Koenigen-kloster, in Altbruenn. He was very successful in {202} his theological studies, and in 1846 he was ordained priest. He seems to have made a striking success as a teacher, especially of natural history and physics, in the higher Realschule in Bruenn. He attracted the attention of his superiors, who were persuaded to give him additional opportunities for the study of the sciences, particularly of biological science, for which he had a distinct liking and special talents.

Accordingly, in 1851 he went to Vienna for the purpose of doing post-graduate work in the natural sciences at the university there. During the two years he spent at this institution he attracted attention by his serious application to study, but apparently without having given any special evidence of the talent for original observation that was in him. In 1853 he returned to the monastery in Altbruenn, and at the beginning of the school year became a teacher at the Realschule in Bruenn. He remained in Bruenn for the rest of his life, dying at the comparatively early age of sixty-two, in 1884. During the last sixteen years of his life he held the position of abbot of the monastery, the duties of which prevented him from applying himself as he probably would have desired, to the further investigation of scientific questions.

The experiments on which his great discoveries were founded were carried out in the garden of the monastery during the sixteen years from 1853 to 1868. How serious was his scientific devotion may be gathered from the fact that in {203} establishing the law which now bears his name, and which was founded on observations on peas, some 10,000 plants were carefully examined, their various peculiarities noted, their ancestry carefully traced, the seeds kept in definite order and entirely separate, so as to be used for the study of certain qualities in their descendants, and the whole scheme of experimentation planned with such detail that for the first time in the history of studies in heredity, no extraneous and inexplicable data were allowed to enter the problem. Besides his work on plants, Mendel occupied himself with other observations of a scientific character on two subjects which were at that time attracting considerable attention. These were the state and condition of the ground-water--a subject which was thought to stand at the basis of hygienic principles at the time and which had occupied the attention of the distinguished Professor Pettenkofer and the Munich School of Hygiene for many years--and weather observations. At that time Pettenkofer, the most widely known of sanitary scientists, thought that he was able to show that the curve of frequency of typhoid fever in the different seasons of the year depended upon the closeness with which the ground-water came to the surface. Authorities in hygiene generally do not now accept this supposed law, for other factors have been found which are so much more important that, if the ground-water has any influence, it can be neglected. Mendel's observations in the matter {204} were, however, in line with the scientific ideas of the time and undoubtedly must be considered of value.

The other subject in which Mendel interested himself was meteorology. He published in the journal of the Bruenn Society of Naturalists a series of statistical observations with regard to the weather. Besides this he organized in connexion with the Realschule in Bruenn a series of observation stations in different parts of the country around; and at the time when most scientists considered meteorological problems to be too complex for hopeful solution, Mendel seems to have realized that the questions involved depended rather on the collation of a sufficient number of observations and the deduction of definite laws from them than on any theoretic principles of a supposed science of the weather.

The man evidently had a genius for scientific observations. His personal character was of the highest. The fact that his fellow-monks selected him as abbot of the monastery shows the consideration in which he was held for tact and true religious feeling. There are many still alive in Bruenn who remember him well and cannot say enough of his kindly disposition, the _froeliche Liebenswuerdigkeit_ (which means even more than our personal magnetism), that won for him respect and reverence from all. He is remembered, not only for his successful discoveries, and not alone by his friends and the fellow-members of the Naturalist Society, but by practically all his {205} contemporaries in the town; and it is his lovable personal character that seems to have most impressed itself on them.

He was for a time the president of the Bruenn Society of Naturalists, while also abbot of the monastery. This is, perhaps, a combination that would strike English-speaking people as rather curious, but seems to have been considered not out of the regular course of events in Austria.

Father Mendel's introduction to his paper on plant hybridization, which describes the result of the experiments made by him in deducing the law which he announces, is a model of simple straightforwardness. It breathes the spirit of the loftiest science in its clear-eyed vision of the nature of the problem he had to solve, the factors which make up the problem, and the experimental observations necessary to elucidate it. We reproduce the introductory remarks here from the translations made of them by the Royal Horticultural Society of England. [Footnote 16] Father Mendel said at the beginning of his paper as read 8 February, 1865:--

[Footnote 16: The original paper was published in the
"Verhandlungen des Naturforscher-Vereins," in Bruenn, Abhandlungen,
iv, that is, the proceedings of the year 1865, which were
published in 1866. Copies of these transactions were exchanged
with all the important scientific journals, especially those in
connexion with important societies and universities throughout
Europe, and the wonder is that this paper attracted so little
attention.]

Experience of artificial fertilization such as is affected with
ornamental plants in order to obtain new variations in color, has
led to the experiments, the {206} details of which I am about to
discuss. The striking regularity with which the same hybrid forms
always reappeared whenever fertilization took place between the same
species, induced further experiments to be undertaken, the object of
which was to follow up the developments of the hybrid in a number of
successive generations of their progeny.

Those who survey the work that has been done in this department up
to the present time will arrive at the conviction that among all the
numerous experiments made not one has been carried out to such an
extent and in such a way as to make it possible to determine the
number of different forms under which the offspring of hybrids
appear, or to arrange these forms with certainty, according to their
separate generations, or to ascertain definitely their statistical
relations.

These three primary necessities for the solution of the problem of heredity--namely, first, the number of different forms under which the offspring of hybrids appear; secondly, the arrangement of these forms, with definiteness and certainty, as regards their relations in the separate generation; and thirdly, the statistical results of the hybridization of the plants in successive generations, are the secret of the success of Mendel's work, as has been very well said by Bateson, in commenting on this paragraph in his work on Mendel's "Principles of Heredity." This was the first time that any one had ever realized exactly the nature of the problems presented in, their naked simplicity. "To see a problem well is more than half to solve it," and this proved to be the case with Mendel's straightforward vision of the nature of the experiments required for advance in our knowledge of heredity.

{207}

While Mendel was beginning his experiments almost absolutely under the guidance of his own scientific spirit, and undertaking his series of observations in the monastery garden without any reference to other work in this line, he knew very well what distinguished botanists were doing in this line and was by no means presumptuously following a study of the deepest of nature's problems without knowing what others had accomplished in the matter in recent years. In the second paragraph of his introduction he quotes the men whose work in this science was attracting attention, and says that to this object numerous careful observers, such a Koelreuter, Gaertner, Herbert, Lecoq, Wichura and others, had devoted a part of their lives with inexhaustible perseverance.

To quote Mendel's own words:--

Gaertner, especially in his work, "Die Bastarderzeugung im
Pflanzenreiche," [Footnote 17] has recorded very valuable
observations; and quite recently Wichura published the results of
some profound observations on the hybrids of the willow. That so far
no generally applicable law governing the formation and development
of hybrids has been successfully formulated can hardly be wondered
at by anyone who is acquainted with the extent of the task and can
appreciate the difficulties with which experiments of this class
have to contend. A final decision can only be arrived at when we
shall have before us the results of the changed detailed experiments
made on plants belonging to the most diverse orders. It requires
some courage indeed to undertake a labor of such far-reaching
extent; it appears, however, to be the only right way by which we
can finally reach the solution of a question the importance of which
can not be overestimated in connexion with the history of the
evolution of organic forms.

The paper now presented records the results of such a detailed
experiment. This experiment was practically confined to a small
plant group, and is now after eight years' pursuit concluded in all
essentials. Whether the plan upon which the separate experiments
were conducted and carried out was the best suited to attain the
desired end is left to the friendly decision of the reader.

[Footnote 17: The Production of Hybrids in the Vegetable Kingdom.]

{208}

Mendel's discoveries with regard to peas and the influence of heredity on them, were founded on very simple, but very interesting, observations. He found that if peas of different colors were taken, that is to say, if, for instance, yellow-colored peas were crossed with green, the resulting pea seeds were, in the great majority of cases, of yellow color. If the yellow-colored peas obtained from such crossing were planted and allowed to be fertilized only by pollen from plants raised from similar seeds, the succeeding generation, however, did not give all yellow peas, but a definite number of yellow and a definite number of green. In other words, while there might have been expected a permanence of the yellow color, there was really a reversion in a number of the plants apparently to the type of the grandparent. Mendel tried the same experiment with seeds of different shape. Certain peas are rounded and certain others are wrinkled. When these were crossed, the next generation {209} consisted of wrinkled peas, but the next succeeding generation presented a definite number of round peas besides the wrinkled ones, and so on as before. He next bred peas with regard to other single qualities, such as the color of the seed coat, the inflation or constriction of the pod, as to the coloring of the pod, as to the distribution of the flowers along the stem, as to the length of the stem, finding always, no matter what the quality tested, the laws of heredity he had formulated always held true.

What he thus discovered he formulated somewhat as follows: In the case of each of the crosses the hybrid character, that is, the quality of the resultant seed, resembles one of the parental forms so closely that the other escapes observation completely or cannot be detected with certainty. This quality thus impressed on the next generation, Mendel called the dominant quality. As, however, the reversion of a definite proportion of the peas in the third generation to that quality of the original parent which did not appear in the second generation was found to occur, thus showing that, though it cannot be detected, it is present, Mendel called it the recessive quality. He did not find transitional forms in any of his experiments, but constantly observed that when plants were bred with regard to two special qualities, one of those qualities became dominant in the resultant hybrid, and the other became recessive, that is, present though latent and ready to produce its effects upon a definite proportion of the succeeding generation.

{210}

Remembering, then, that Mendel means by hybrid the result of the crossing of two distinct species, his significant discovery has been stated thus: The hybrid, whatever its own character, produces ripe germ cells, which bear only the pure character of one parent or the other. Thus, when one parent has the character "A," in peas, for example, a green color, and the other the character "B," in peas once more a yellow color, the hybrid will have in cases of simple dominance the character "AB" or "BA," but with the second quality in either case not noticeable. Whatever the character of the hybrid may be, that is to say, to revert to the example of the peas, whether it be green or yellow, its germ cells when mature will bear either the character "A" (green), or the character "B" (yellow), but not both.

As Professor Castle says: "This perfectly simple principle is known as the law of segregation, or the law of the purity of the germ cells. It bids fair to prove as fundamental to a right understanding of the facts of heredity as is the law of definite proportions in chemistry. From it follow many important consequences."

To follow this acute observer's work still further by letting the crossbreds fertilize themselves, Mendel raised a third generation. In this generation were individuals which showed the dominant character and also individuals which presented the recessive character. Such an observation had of course been made in a good many instances before.

{211}

But Mendel noted--and this is the essence of the new discovery in his observations--that in this third generation the numerical proportion of dominants to recessives is in the average of a series of cases approximately constant--being, in fact, as three to one. With almost absolute regularity this proportion was maintained in every case of crossing of pairs of characters, quite opposed to one another, in his pea plants. In the first generation, raised from his crossbreds, or, as he calls them, hybrids, there were seventy-five per cent dominants and twenty-five per cent recessives.

When these plants were again self-fertilized and the offspring of each plant separately sown, a new surprise awaited the observer. The progeny of the recessives remained pure recessive; and in any number of subsequent generations never produced the dominant type again, that is, never reverted to the original parent, whose qualities had failed to appear in the second generation. When the seeds obtained by self-fertilizing the plants with the dominant characteristics were sown, it was found by the test of progeny that the dominants were not all of like nature, but consisted of two classes--first, some which gave rise to pure dominants; and secondly, others which gave a mixed offspring, composed partly of recessives, partly of dominants. Once more, however, the ratio of heredity asserted itself and it was found that the average numerical proportions were constant--those with pure dominant {212} offspring being to those with mixed offspring as one to two. Hence, it was seen that the seventy-five per cent of dominants are not really of identical constitution, but consist of twenty-five per cent which are pure dominants and fifty per cent which are really crossbreds, though like most of the crossbreds raised by crossing the two original varieties, they exhibit the dominant character only.

These fifty crossbreds have mixed offspring; these offspring again in their numerical proportion follow the same law, namely, three dominants to one recessive. The recessives are pure like those of the last generation, but the dominants can, by further self-fertilization and cultivation of the seeds produced, be again shown to be made up of pure dominant and crossbreds in the same proportion of one dominant to two crossbreds.

The process of breaking up into the parent forms is thus continued in each successive generation, the same numerical laws being followed so far as observation has gone. As Mendel's observations have now been confirmed by workers in many parts of the world, investigating many different kinds of plants, it would seem that this law which he discovered has a basis in the nature of things and is to furnish the foundation for a new and scientific theory of heredity, while at the same time affording scope for the collection of observations of the most valuable character with a definite purpose and without any theoretic bias.

{213}

The task of the practical breeder who seeks to establish or fix a new variety produced by cross-breeding in a case involving two variable characters is simply the isolation and propagation of that one in each sixteen of the second generation offspring which will be pure as regards the desired combination of characters. Mendel's discovery, by putting the breeder in possession of this information enables him to attack this problem systematically with confidence in the outcome, whereas hitherto his work, important and fascinating as it is, has consisted largely of groping for a treasure in the dark. The greater the number of separately variable characters involved in a cross, the greater will be the number of new combinations obtainable; the greater too will be the number of individuals which it will be necessary to raise in order to secure all the possible combinations; and the greater again will be the difficulty of isolating the pure, that is, the stable forms in such as are similar to them in appearance, but still hybrid in one or more characters.

The law of Mendel reduces to an exact science the art of breeding in the case most carefully studied by him, that of entire dominance. It gives to the breeder a new conception of "purity." No animal or plant is "pure," simply because it is descended from a long line of ancestors, possessing a desired combination of characters; but any animal or plant is pure if it produces _gametes_--that is, particles for conjugation of only one sort--even though its grandparents may among {214} themselves have possessed opposite characters. The existence of purity can be established with certainty only by suitable breeding tests, especially by crossing with recessives; but it may be safely assumed for any animal or plant, descended from parents which were like each other and had been shown by breeding tests to be pure.

This naturally leads us to what some biologists have considered to be the most important part of his work--the theory which he elaborated to explain his results, the principle which he considers to be the basis of the laws he discovered. Mendel suggests as following logically from the results of his experiments and observations a certain theory of the constitution of germinal particles. He has put this important matter so clearly himself and with such little waste of words that it seems better to quote the translation of the passage as given by Professor Bateson, [Footnote 18] than to attempt to explain it in other words. Mendel says:--

[Footnote 18: Bateson: _Mendel's Principles of Heredity_.
Cambridge. The University Press. 1902.]

The results of the previously described experiments induced further
experiments, the results of which appear fitted to afford some
conclusions as regards the composition of the egg and pollen-cells
of hybrids. An important matter for consideration is afforded in
peas (_pisum_) by the circumstance that among the progeny of the
hybrids constant forms appear, and that this occurs, too, in all
combinations of the associated characters. So far as experience
goes, we find it in every {215} case confirmed that constant progeny
can only be formed when the egg-cells and the fertilizing pollen are
of like character, so that both are provided with the material for
creating quite similar individuals, as is the case with the normal
fertilization of pure species.

We must therefore regard it as essential that exactly similar
factors are at work also in the production of the constant forms in
the hybrid plants. Since the various constant forms are produced in
one plant, or even in one flower of a plant, the conclusion appears
logical that in the ovaries of the hybrids there are formed as many
sorts of egg-cells and in the anthers as many sorts of pollen-cells
as there are possible constant combination forms, and that these egg
and pollen-cells agree in their internal composition with those of
the separate forms.

In point of fact, it is possible to demonstrate theoretically that
this hypothesis would fully suffice to account for the development
of the hybrids in the separate generations, if we might at the same
time assume that the various kinds of egg and pollen-cells were
formed in the hybrids on the average in equal numbers.

Bateson says in a note on this passage that this last and the preceding paragraph contain the essence of the Mendelian principles of heredity. Mendel himself, after stating this hypothesis, gives the details of a series of experiments by which he was able to decide that the theoretic considerations suggested were founded in the nature of plants and their germinal cells.

It will, of course, be interesting to realize what the bearing of Mendel's discoveries is on the question of the stability of species as well as on the origin of species. Professor Morgan, in his {216} article on Darwinism in the "Light of Modern Criticism," already quoted, says the important fact (with regard to Mendel's Law) from the point of view of the theory of evolution is that "the new species have sprung fully armed from the old ones, like Minerva from the head of Jove." "From de Vries's results," he adds, "we understand better how it is that we do not see new forms arising, because they appear, as it were, fully equipped over night. Old species are not slowly changed into new ones, but a shaking up of the old organization takes place and the egg brings forth a new species. It is like the turning of the kaleidoscope, a slight shift and the new figure suddenly appears. It needs no great penetration to see that this point of view is entirely different from the conception of the formation of new species by accumulating individual variations, until they are carried so far that the new form may be called a new species."

With regard to this question of the transformation of one species into another, Mendel himself, in the concluding paragraphs of his article on hybridization, seems to agree with the expressions of Morgan. He quotes Gaertner's opinion with apparent approval: "Gaertner, by the results of these transformation experiments was led to oppose the opinion of those naturalists who dispute the stability of plant species and believe in a continuous evolution of vegetation. He perceives in the complete transformation of one species into another an indubitable proof that {217} species are fixed within limits beyond which they cannot change." "Although this opinion," adds Mendel, "cannot be unconditionally accepted, we find, on the other hand, in Gaertner's experiments a noteworthy confirmation of that supposition regarding the variability of cultivated plants which has already been expressed." This expression of opinion is not very definite, and Bateson, in what Professor Wilson of Columbia calls his "recent admirable little book on Mendel's principles," adds the following note that may prove of service in elucidating Mendel's meaning, as few men have entered so fully into the understanding of Mendel's work as Bateson, who introduced him to the English-speaking scientific public, "The argument of this paragraph appears to be that though the general mutability of natural species might be doubtful, yet among cultivated plants the transference of characters may be accomplished and may occur by _integral steps_ [italics ours], until one species is definitely 'transformed' into the other."

Needless to say, this is quite different from the gradual transformation of species that Darwinism or Lamarckism assumes to take place. One species becomes another _per saltum_ in virtue of some special energy infused into it, some original tendency of its intrinsic nature, not because of gradual modification by forces outside of the organisms, nor because of the combination of influences they are subjected to from without and within, because of tendency to evolute plus {218} environmental forces. This throws biology back to the permanency of species in themselves, though successive generations may be of different species, and does away with the idea of missing links, since there are no gradual connecting gradations.

A very interesting phase of Mendel's discoveries is concerned with the relative value of the egg-cell and the pollen-cell, as regards their effect upon future generations. It is an old and oft-discussed problem as to which of these germinal particles is the more important in its influence upon the transmission of parental qualities. Mendel's observations would seem to decide definitely that, in plants and, by implication, in animals, since the germinal process is biogenetically similar, the value of both germinal particles is exactly equal.

In a note, Mendel says:--

_In pisum_ (i. e. in peas), it is beyond doubt that, for the
formation of the new embryo, a perfect union of the elements of both
fertilizing cells must take place. How could we otherwise explain
that, among the offspring of the hybrids, both original types
reappear in equal numbers, and with all their peculiarities? If the
influence of the egg-cell upon the pollen-cell were only external,
if it fulfilled the role of a nurse only, then the result of each
artificial fertilization could be no other than that the developed
hybrid should exactly resemble the pollen parent, or, at any rate,
do so very closely. These experiments, so far, have in no wise been
confirmed. An evident proof of the complete union of the contents of
both cells is afforded by the {219} experience gained on all sides,
that it is immaterial as regards the form of the hybrid which of the
original species is the seed cell, or which the pollen parent!

This is the first actual demonstration of the equivalent value of both germinal particles as regards their influence on transmission inheritance in future generations.

It is only by simplifying the problem so that all disturbing factors could be eliminated that Mendel succeeded in making this demonstration. Too many qualities have hitherto been considered with consequent confusion as to the results obtained.

It is of the genius of the man that he should have been able to succeed in seeing the problem in simple terms while it is apparently so complex, and thus obtain results that are as far-reaching as the problem they solve is basic in its character.

Bateson, in his work Mendel's _Principles of Heredity_, says:--

It may seem surprising that a work of such importance should so long
have failed to find recognition and to become current in the world
of science. It is true that the Journal in which it appeared is
scarce, but this circumstance has seldom long delayed general
recognition. The cause is unquestionably to be found in that neglect
of the experimental study of the problem of species which supervened
on the general acceptance of the Darwinian doctrine. The problem of
species, as Koelreuter, Gaertner, Naudin, Wichura, and the hybridists
of the middle of the nineteenth century conceived it, attracted
thenceforth no workers.

{220}

The question, it was imagined, had been answered and the debate
ended. No one felt much interest in the matter. A host of other
lines of work was suddenly opened up, and in 1865 the more original
investigators naturally found these new methods of research more
attractive than the tedious observations of hybridizers, whose
inquiries were supposed, moreover, to have led to no definite
results.

In 1868 appeared the first edition of Darwin's _Animals and Plants_,
marking the very zenith of these studies with regard to hybrids and
the questions in heredity which they illustrate, and thenceforth the
decline in the experimental investigation of evolution and the
problem of species have been studied. With the rediscovery and
confirmation of Mendel's work by de Vries, Correns and Tschermak in
1900 a new era begins. Had Mendel's work come into the hands of
Darwin it is not too much to say that the history of the development
of evolutionary philosophy would have been very different from that
which we have witnessed.

That Mendel's work, appearing as it did at a moment when several
naturalists of the first rank were still occupied with these
problems, should have passed wholly unnoted, will always remain
inexplicable, the more so as the Bruenn society exchanged its
publication with most of the great academies of Europe, including
both the Royal and the Linnean societies of London.

The whole history of Mendel's work, its long period without effect upon scientific thought, its thoroughly simple yet satisfactory character, its basis in manifold observations of problems simplified to the last degree, and its present complete acceptance illustrate very well the chief defect of the last two generations of workers in biology. {221} There has been entirely too much theorizing, too much effort at observations for the purpose of bolstering up preconceived ideas--preaccepted dogmas of science that have proved false in the end--and too little straightforward observation and simple reporting of the facts without trying to have them fit into any theory prematurely, that is until their true place was found. This will be the criterion by which the latter half of nineteenth century biology will be judged; and because of failure here much of our supposed progress will have no effect on the current of biological progress, but will represent only an eddy in which there was no end of bustling movement manifest but no real advance.

As stated very clearly by Professor Morgan at the beginning of this paper, and Professor Bateson near the end, Darwin's doctrine of natural selection as the main factor in evolution and its practically universal premature acceptance by scientific workers in biology are undoubtedly responsible for this. The present generation may well be warned, then, not to surrender their judgment to taking theories, but to wait in patience for the facts in the case, working, not theorizing, while they wait.

End of Project Gutenberg's Catholic Churchmen in Science, by James J. Walsh

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