is supposed that the training of a clergyman and particularly that of
a religious unfits him for any such initiative in science, Father
Mendel's discovery comes with all the more emphatic surprise. There is
no doubt, however, in the minds of many of the most prominent
present-day workers in biology that his {197} discoveries are of a
ground-breaking character that will furnish substantial foundation for
a new development of scientific knowledge with regard to heredity.
Lest it should be thought that perhaps there is a tendency to make
Father Mendel's discovery appear more important here than it really
is, because of his station in life, it seems desirable to quote some
recent authoritative expressions of opinion with regard to the value
of his observations and the importance of the law he enunciated, as
well as the principle which he considered to be the explanation of
that law.
In the February number of _Harper's Monthly_ for 1903, Professor
Thomas Hunt Morgan, Professor of Biology at Bryn Mawr, and one of the
best known of our American biologists, whose recent work on
"Regeneration" has attracted favorable notice all over the world,
calls attention to the revolutionary character of Mendel's discovery.
He considers that recent demonstrations of the mathematical truth of
Mendel's Law absolutely confirm Mendel's original observations, and
the movement thus initiated, in Professor Morgan's eyes, gives the
final _coup de grace_ to the theory of natural selection. "If," he
says, "we reject Darwin's theory of natural selection as an
explanation of evolution, we have at least a new and promising outlook
in another direction and are in a position to answer the oft-heard but
unscientific query of those who must cling to some dogma: if you
reject Darwin, what better have you to offer?"
{198}
Professor Edmund B. Wilson, the Director of the Zoological Laboratory
of Columbia University, called attention in _Science_ (19 December,
1902) to the fact that studies in cytology, that is to say,
observations on the formation, development, and maturation of cells,
confirm Mendel's principles of inheritance and thus furnish another
proof of the truth of these principles.
Two students working in Professor Wilson's laboratory have obtained
definite evidence in favor of the cytological explanation of Mendel's
principles, and have thus made an important step in the solution of
one of the important fundamental mysteries of cell development in the
very early life of organisms.
In a paper read before the American Academy of Arts and Sciences last
year, Professor W. E. Castle, of Harvard University, said with regard
to Mendel's Law of Heredity:--
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.