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“There is no doubt that man, as an animal, inherits characteristics, good
and evil, as do animals and plants”.
Thomas Hunt Morgan (1866-1945)
Zoologist
Faculty 1904-28
Morgan's studies on inherited characteristics of the fruit
fly laid the foundations of modern genetics and led to
such advances as the deciphering of the human genome.
His work earned him the 1933 Nobel Prize in Physiology
or Medicine, making him the first native-born American
to receive that honor. He also authored classic texts in
genetics including Heredity and Sex (1913), The Physical
Basis of Heredity (1919), Embryology and Genetics
(1924), Evolution and Genetics (1925), The Theory of the
Gene (1926), Experimental Embryology (1927), and The
Scientific Basis of Evolution (1932).
Morgan received his PhD in developmental biology from Johns Hopkins University in
1890 and taught at Bryn Mawr College before arriving at Columbia in 1904 to assume
a newly established chair in experimental zoology. In 1910, he began his study of
Drosophila melanogaster, the insect with which his name will always be associated. It
was working with undergraduate students Calvin Bridges and Alfred Sturtevant, and
in Schemerhorn Hall's "Fly Room" with graduate and postdoctoral scientists such as
Hermann J. Mueller and George Beadle, that Morgan discovered the chromosomal
basis for the inheritance of traits. He left Columbia in 1928 to serve as chair of the
Biology Division at the California Institute of Technology
THOMAS HUNT MORGAN AT COLUMBIA UNIVERSITY
Genes, Chromosomes, and the Origins of Modern Biology
Eric R Kandel
The student of the humanities as well as the intelligent public looks at the history of
human thought as a history of abstract ideas. . . . It is true that minds like those of Plato,
Thomas Aquinas, Spinoza, Descartes, Hegel and Kant have exercised a strong influence
upon the progress of thinking in all spheres, even upon the actual course of historical
events. The scientist who looks beyond his specialized work is as fully aware of these
historical facts as the humanist. But he is also aware that abstract thinking, remote
from, and even antagonistic to the study of nature, leads easily into dogma, taboos and
fettering of free thinking because it does not carry its own corrective, the recourse to
factual evidence. The scientist, therefore, with all respect for the many facets of the
human mind, is more impressed by the revolutions in thinking brought about by great
factual discoveries, which by their very nature lead to generalizations which change at
once the outlook of many, if not all, lines of thought. Such events are rare. In modern
history three are most conspicuous: the explanation of the movements of the celestial
bodies by Kepler, Copernicus and Newton; Galileo's experiments inaugurating the age of
inductive science, and Darwin's establishment of the theory of evolution on the basis of
an overwhelming body of facts. All of them at once evoked the wrath of the vested
interests of the mind; all conquered within a generation or two all fields of intellectual
endeavor and changed the basic aspects of practically every science, natural or
humanistic.
. . . . the rise and development of genetics to mature age is another instance of an allcomprising and all-affecting generalization based upon an overwhelming body of
integrated facts, . . . [and] will rank in the history of science with such other great events
as mentioned, . . . The basic tenets of genetics have already influenced decisively all parts
of biology after what has been only a short span in the history of science; and further
that beyond this, many other fields of science have fallen under the spell and we have
every reason to believe that genetics is bound to remain in a pivotal position in the
future.
-Richard B. Goldschmidt, The Impact of Genetics Upon Science (1950)
When future historians turn to examine the major intellectual accomplishments of the
twentieth century, they will undoubtedly give a special place to the extraordinary
achievements in biology, achievements that have revolutionized our understanding of
life's processes and of disease. Important intimations of what was to happen in
biology were already apparent in the second half of the nineteenth century. Darwin
had delineated the evolution of animal species, Mendel had discovered some basic
rules about inheritance, and Weissman, Roux, Driesch, de Vries, and other
embryologists were beginning to decipher how an organism develops from a single
cell. What was lacking at the end of the nineteenth century, however, was an
overarching sense of how these bold advances were related to one another.
The insight that unified these three fields- heredity,
evolution, and development- and set biology on the
course toward its current success came only at the
beginning of the twentieth century. It derived from
the discovery that the gene, localized to specific
positions on the chromosome, was at once the unit of
Mendelian heredity, the driving force for Darwinian
evolution, and the control switch for development.
This remarkable discovery can be traced directly to
one person and to one institution: Thomas Hunt
Morgan and Columbia University. Much as Darwin's
insights into the evolution of animal species first gave
coherence to nineteenth-century biology as a
descriptive science, Morgan's findings about genes
and their location on chromosomes helped transform
biology into an experimental science.
Even more important, Morgan's discoveries made it possible to address a series of
questions regarding the function and structure of genes. What is their chemical
nature? How do genes duplicate themselves? What goes wrong when genes mutate?
How do genes provide the basis for understanding genetic disease? How do genes
determine the properties of cells, the development of organisms, and the course of
evolution? Answers to some of these questions came directly from Morgan and his
students; while other advances were the work of scientists touched by his broader
influence. In every case, the discoveries made by these pioneering researchers set the
agenda for biology in the twentieth century.
For example, George Beadle, who trained with Morgan and with Morgan's student
Alfred Sturtevant '12C '14GSAS, joined Edward L. Tatum to examine how genes
determine the properties of the cell. In addressing this problem, they discovered that
genes control the synthesis of the cell's proteins, many of which are enzymes. Then
Oswald T. Avery '04P&S, another graduate of Columbia, teamed with Maclyn McCarty
and Colin MacLeod at the Rockefeller Institute for Medical Research to show that the
transforming genetic material is made of DNA. Theodosius Dobzhansky '64HON, a
postdoctoral fellow of Morgan's, related genetic mutations to evolutionary change.
Hermann J. Muller '10C '11 '16GSAS, another Morgan student, discovered that Xirradiation dramatically increases the rate at which mutations occur, an advance that
focused attention on the role of environmentally induced and inherited gene
mutations in important diseases ranging from cancer to Huntington's disease and
schizophrenia. Joshua Lederberg '44C, an academic grandchild of Morgan, discovered
transduction -the ability of viruses to carry exogenous genes into a bacterial cell- the
first step on the road to genetic engineering. James D. Watson and Francis Crick next
showed that DNA has a double helical conformation, a chemical conformation that
immediately led to an understanding of how DNA and genes are replicated. Edward B.
Lewis, another academic grandchild of Morgan, used genetics to probe development
and found that a special set of genes determines the organization of the body plan.
Thus, biology at the beginning of the twenty-first century represents, in good part, the
molecular realization of the ideas and way of thinking introduced at the beginning of
the twentieth century by Thomas Hunt Morgan at Columbia University.
Morgan and the Mechanisms of Mendelian Heredity
Thomas Hunt Morgan was born in Kentucky in 1866 to a distinguished southern
family whose members included Francis Scott Key. Morgan was trained as a
developmental biologist, receiving his Ph.D. in 1890 from the Johns Hopkins
University for work on the development of sea spiders, a specialized group of
invertebrate animals, and in 1891 he accepted a teaching post at Bryn Mawr College.
In 1904 Columbia University announced the establishment of a new chair in
experimental zoology and offered it to Morgan. Arriving on campus, he came under
the influence of his long-term friend and colleague, the zoology department's
chairman, Edwin Wilson, one of the eminent cytologists of his time and a founder of
the field of cell biology. Wilson convinced Morgan that the key to understanding
development—how one cell, the egg, gives rise to the animal—is to understand
heredity, since it provides the means by which the egg and the sperm carry the
properties of individuals from one generation to another.
Later findings proved Wilson correct, and we now know that the human genome
consists of 46 chromosomes, arranged in 22 pairs of autosomes (not linked to sex),
and one pair of sex chromosomes (two X chromosomes in females, one X and one Y
chromosome in males). The 100,000 genes in our genome are arranged along the
chromosomes in precise order, with each being uniquely identifiable by its location at
a characteristic position (locus) on a specific chromosome. The two copies of a gene at
corresponding loci on each pair of chromosomes are known as alleles.
The modern concepts of heredity and the existence of alternative (allelic) forms of
genes had been discovered in 1865 by Gregor Mendel, a teacher and monk of the
Augustinian monastery in Brno, then part of the Austro-Hungarian empire. Mendel
carried out breeding experiments with plants, especially garden peas, and identified
hereditary traits in them. These traits, later called factors, were found by Mendel to
account for such features as whether peas were wrinkled or smooth and for the
differences between dominant and recessive alleles; he did not know, however, where
these traits were located or what they were. Mendel's findings were published in the
Proceedings of the Natural Science Society of Brno in 1866, only to be ignored until the
turn of the century. His work was rediscovered in 1900, just before Morgan arrived at
Columbia.
In taking up his own inquiries, Morgan turned from Mendel's
plants to the study of animals, but soon found that the rats and
mice he was using reproduced so slowly as to be impractical
for studying heredity. His search for a more suitable organism
led him to Drosophila melanogaster, known as the fruit fly
because it feeds on decaying fruit. Drosophila is small, about 3
mm long, and easy to raise in the laboratory -a thousand can be
collected in a one-quart glass milk bottle. Moreover, it is fertile
all year long and very prolific, producing a new generation
every twelve days, or thirty generations per year. Not only are
male and female offspring easy to distinguish, but embryonic
development occurs outside the body, making it a simple matter to study the effects of
mutations on development. Finally, Drosophila has only four pairs of chromosomes.
Morgan began working seriously with Drosophila in 1907, with the intention of
breeding many generations of flies, and perhaps producing one that looked different
from the rest. In short, he hoped to find an occasional fly that had undergone a
mutation, sudden change in body form, a phenomenon that had recently been
discovered in plants by the Dutch biologist Hugo de Vries. But despite much effort and
the breeding of successive generations, Morgan initially failed to detect a single
mutation. "Two years work wasted," he lamented to one visitor to his laboratory. "I
have been breeding those flies for all that time and I've got nothing out of
it."(Harrison, R.G., "Embryology and Its Relations")
Year of Discovery
But Morgan persisted, and in April 1910 he suddenly had a breakthrough. In one of his
bottles filled with Drosophila was a male fly with rather than the normal red eyes.
Morgan realized the implications of this immediately; the birth of this single
spontaneous mutant—this one male fly with white eyes—allowed him to begin
addressing some key questions in heredity: How did this white eye color originate?
What determines eye color?
As the next step, Morgan bred this white-eyed (mutant) male to a red-eyed (wildtype) virgin sister and found that white-colored eyes are inherited in a special way. In
the first generation of brother-sister mating, labeled F1, there were only red-eyed
offsprings, suggesting that red eye color is dominant and that white eye color is
recessive. To prove this idea Morgan carried out brother-sister matings with the next
generation (F2) and found that the offspring followed the expected Mendelian ratio
for a recessive trait: three red-eyed flies to every one white-eyed fly. With these
experiments Morgan started a tradition, which continues to this day, whereby he
named the gene "white" by the result of its mutation. But then came a surprise. He had
expected there would be an equal number of males and females with white eyes, but it
turned out that all the female flies had red eyes; only males had white eyes, and, even
more, only some of them displayed the trait. Morgan realized that white eye color is
not only recessive but is also linked in some way to sex. The subsequent appearance of
two other spontaneous mutations (rudimentary wings and yellow body color) also
linked to sex further suggested to Morgan that these three genes might be carried on
the same chromosome and that this chromosome is the sex chromosome.
By 1910, it was already known that chromosomes occur in pairs and that Drosophila
had four pairs of chromosomes. Several decades earlier, these thread-shaped
structures had been seen under a microscope to be located in the nucleus, but nobody
knew their function. Morgan later was to describe them in the following terms:
"The egg of every species of animal or plant carries a definite number of bodies called
chromosomes. The sperm carries the same number. Consequently, when the sperm unites
with the egg, the fertilized egg will contain the double number of chromosomes. For each
chromosome contributed by the sperm there is a corresponding chromosome
contributed by the egg, i.e., there are two chromosomes of each kind, which together
constitute a pair." (Morgan, T.H. et al., The Mechanism of Mendelian Heredity)
When Morgan turned to examining the fruit fly's chromosomes under the microscope,
he immediately appreciated that not all four pairs of chromosomes were always
identical. In particular, whereas female flies had two identical-looking X
chromosomes, in the male the X chromosome was paired with a Y chromosome, which
looks different and is never present in the female.
Morgan deduced that a male must inherit the X chromosome from his mother and Y
from his father, and he immediately spotted a correlation between these sex-linked
chromosomes and the segregation of the factors determining eye color. When the
mother was homozygous and had two copies of the gene for red eyes, the male
offspring invariably had red eyes, even if the father had white eyes. But when the
mother had white eyes, the male offspring did too, even if the father's eyes were red.
In contrast, a female fly gets one X chromosome from each parent, and if one passed
along an X chromosome with a gene for red eyes, the offspring had red eyes because
the color is dominant over white. Only when both parents gave her an X chromosome
with a gene for white eyes did she display the recessive trait. From these observations,
Morgan concluded that the allele-producing eye color must lie on the X chromosome
that governs sex. This provided the first correlation between a specific trait and a
specific chromosome.
Morgan's initial paper on fruit flies, entitled "Sex Limited Inheritance in Drosophila,"
was published in Science in July 1910. In this and in a subsequent paper published in
Science in 1911, Morgan outlined his three major findings: (1) that genes must reside
on chromosomes; (2) that each gene must reside on a particular chromosome; and (3)
that the trait for eye color must reside on the sex chromosome, with the eye-color
locus (or white gene) being missing on the Y chromosome and red being dominant on
the X chromosome.
These findings formed the heart of Morgan's most important idea: the chromosomal
theory of heredity. He proposed that each chromosome contains a collection of small
units called genes (a term he adopted from the Danish physiologist Wilhelm
Johannsen who had lectured at Columbia in 1909), with different genes having
specific locations along specific chromosomes. Once this idea formed in his mind,
Morgan sensed that the experimental power of the fly would allow him to understand
heredity.
A focus on chromosomes and their morphology was not what Morgan had in mind
when he started to work on flies. In fact, until he saw the white-eyed mutant and
appreciated that its defect acted as if it were part of the X chromosome, he had been
skeptical about Mendel's theory of heredity and Mendel's factors. Now that he had
seen the possibility that these factors might have a physical reality as genes on
chromosomes, Morgan began to view the Mendelian theory in a new light.
A Legacy of Accomplishment
As early as 1911, Morgan had redirected his research in an attempt to provide
additional information about the chromosome theory of heredity, and before long he
achieved another major conceptual breakthrough. Since chromosomes are contiguous
assemblages of genes, those traits (mutations in some of the genes) mapping to one
particular chromosome naturally tended to segregate together. But on occasion
Morgan noted that these "linked" traits would separate, even while other traits on the
same chromosome showed little or even no detectable linkage.
From this evidence, Morgan inferred the process of chromosome recombination: he
postulated that the two paired chromosomes could "exchange" or "crossover"
between each other, and he further proposed that the frequency of recombination is a
function of the distance between genes on the chromosome. The nearer two relevant
genes lie on a chromosome, the greater their chance of being inherited together, while
the farther away they are from each other, the more chance of their being separated
by the process of crossing over. In short, Morgan suggested that the strength of
linkage between genes depended on the distance between them on the chromosome.
On the basis of these observations, Alfred Henry Sturtevant '12C '14GSAS, then an
undergraduate at Columbia College, who was working with Morgan, recognized that
the variations in the strength of linkage could be used as a means of mapping genes on
chromosomes by determining their relative spatial distances apart. As Sturtevant
himself later recalled:
"I suddenly realized that the variations in the strength of linkage already attributed by
Morgan to difference in the spatial separation of the gene offered the possibility of
determining sequence in the linear dimensions of a chromosome. I went home and spent
most of the night (to the neglect of my undergraduate homework) in producing the first
chromosome map. . . ." (Sturtevant, A.H., Unpublished interview with G.E. Allen)
The Morgan is now the unit of measurement of distances along all chromosomes in fly,
mouse, and humans.
A year after Morgan had spotted the white-eyed fly, Sturtevant drew up the first
genetic map for the sex-linked genes. A sufficient number of mutations had by then
been observed to allow him to express the strength of linkage in units of distance on a
chromosome. In fact, the order and spacing that Sturtevant worked out in 1911 are
essentially those found on modern maps of the Drosophila X chromosome. The
profound insight that genes are aligned on the chromosome like beads on a string
with specific distances between them eventually produced a conceptual basis for
hunting for disease genes through linkage analysis and for mapping whole genomes,
such as the human genome. All this was accomplished by a nineteen-year-old
Columbia third-year undergraduate by simply skipping one night's homework!
Morgan, who was not given to overstatement, later was to call the realization that
genes could be precisely mapped in relation to one another on the chromosome as
"one of the most amazing developments in the history of biology." (Shine, I. and
Wrobel, S., Thomas Hunt Morgan: Pioneer of Genetics)
By correlating breeding results with cytological observations of chromosomes under
the microscope, Morgan's group rapidly transformed the abstract idea of Mendel's
hypothetical factors into the physical reality of particular genes located at specific loci
along the length of the chromosome. Initially their maps were quite abstract, since
they were based only on the relative positions of genes to one another on the
chromosome, as determined by linkage analysis -the sort of map now called a
recombination map. But two decades later Calvin Bridges '12C '16GSAS succeeded in
developing a second independent map -a physical one- showing the exact physical
location of a gene on a chromosome. He accomplished this by exploiting an
unanticipated advantage of Drosophila, which in its larval stages has chromosomes in
its salivary glands that Theophilus Painter discovered to be multistranded and
gigantic, much larger than the chromosomes of the other cells of the body. These giant
chromosomes show a pattern of bands or stripes that divide each chromosome into
physical subregions, and Bridges was ultimately able to recognize 1,024 invariant
bands on the X chromosome. The development of physical maps proved especially
valuable because they allowed a visual presentation of the sequence of genes on the
chromosome -a sequence that can only be inferred from the abstract recombination
map.
By 1913 Sturtevant contributed yet another major breakthrough with his insight into
the existence of different allelic forms, which he saw as alternative states (alleles) of
the same gene at the same locus. Research on the white-eyed gene clearly revealed
that a gene could mutate from one allele to another -from red to white. In some rare
instances, a red allele was observed to mutate to a different allele, then to a third and
eventually a fourth, with each new allele corresponding to a different eye color. But
every time a gene gave rise to a new allele, the mutant form was perpetuated in the
offspring and remained unchanged unless -again, in very rare cases- a new mutation
occurred in one of the offspring. Thus, Morgan's group was able to show that alleles
are remarkably stable!
The low frequency of spontaneous mutation and the perpetuation of mutations that
did occur indicated that genetic material is constant. The observation was soon
confirmed in many other organisms, from Drosophila to man and from bacteria to
yeast, offering proof both of inheritance and of the capacity for mutation to allow for
evolutionary change in spite of the general constancy of genetic material.
These seminal findings were summarized in 1915 by Morgan and his three Columbia
students, Sturtevant, Bridges, and Hermann J. Muller, in The Mechanism of Mendelian
Heredity, a book that proved to be of historic importance. To begin with, it set forth
the physical basis for the new science of genetics. On top of that, the experimental
discipline outlined in its pages provided the first experimental basis for a modern
biology, transforming it from a descriptive science that relied heavily on morphology.
Anatomy, the queen of the biological sciences from the time of the Renaissance to the
beginning of the twentieth century, was now replaced by genetics as biology itself
emerged as an exact, rigorous, quantitative experimental science that could exist on
an equal footing with physics and chemistry.
In recognition of his work on chromosomes, Morgan was awarded the Nobel Prize in
Physiology or Medicine in 1933. He shared the prize money with Bridges and
Sturtevant. The Nobel Prize recognized Morgan's two fundamental scientific
contributions: the development of the chromosome theory of heredity, a theory of the
gene that proved to be the driving biological concept of the twentieth century, and the
creation of a new biology based on a rigorous experimental method.
The Columbia Environment: The Fly Room
Morgan also made a third contribution, a sociological one that helped introduce at
Columbia and into American science as a whole a set of sweeping institutional
changes. Until the start of the twentieth century, the leading American research
universities -Harvard, Johns Hopkins, Columbia, and Chicago- had all been inspired by
the model of the German research university, in which the Geheimrat, the great
scientific leader, ordered the hierarchy of his subordinates. Morgan, however, based
laboratory governance on democratic principles of merit rather than seniority. If one
were to ask scientists around the world what is unique about America, they point to
the university, and to this day foreign scientists are amazed that students working in a
laboratory call professors by their first names.
Morgan surrounded himself with a brilliant group of undergraduate and graduate
students. Together they set up the Drosophila laboratory in Schermerhorn Hall, Room
613, known worldwide as the Fly Room. In retrospect, the Fly Room seems
surprisingly small, measuring only 16 x 23 feet and containing eight desks. Yet, it
housed a stream of Columbia students as well as foreign visitors and soon received
wide recognition, not only for the remarkable quality and clarity of its science but also
for the democratic nature of its social interaction. Morgan encouraged the free
exchange of ideas in an atmosphere that was at once friendly, yet self-critical. The
atmosphere in the Fly Room was described by Sturtevant, one of the youngest in the
group. He wrote:
"This group worked as a unit. Each carried on his own experiments, but each knew
exactly what the others were doing, and each new result was freely discussed. There was
little attention paid to priority or to the source of new ideas or new interpretations.
What mattered was to get ahead with the work. There was much to be done; there were
many new ideas to be tested, and many new experimental techniques to be developed.
There can have been few times and places in scientific laboratories with such an
atmosphere of excitement and with such a record of sustained enthusiasm. This was due
in part to Morgan's own attitude, compounded with enthusiasm combined with a strong
critical sense, generosity, open-mindedness, and a remarkable sense of humor."
(Sturtevant, A.H., Thomas Hunt Morgan: Biographical Memoirs)
Although this idyllic view was not shared by all,* the Fly Room nevertheless
characterized science at its best and continues to provide a prototype for how
research should be done, at Columbia and elsewhere. In terms of the work conducted
there, the science that began at Columbia spread to laboratories all over the world as
Morgan, the members of his group, and the scientists they trained helped to shape the
course of biology during the decades that followed. Of the people who worked with
Morgan directly or who worked with one of his students, five went on to win their
own Nobel Prize: Muller, Beadle, Lederberg, and Lewis. Another student, Dobzhansky,
went on to place evolution into a modern biological context. Impelled by their
achievements, the center of influence in biology shifted from Europe to the United
States, making the twentieth century an American Century in biology.
At the same time, the open, critical, yet fully democratic and egalitarian atmosphere
that was evident in the Fly Room soon came to characterize the distinctively American
atmosphere of university research -an especially significant development as American
graduate education increasingly became the model for graduate education throughout
the world.
I have benefited from the comments on this essay by Garland Allen, Norman Horowitz,
Tom Jessell, Joshua Lederberg, E.B. Lewis, Robert Merton '85HON, Gary Struhl, Andrew
Tomlinson, and Harriet Zuckerman '65GSAS.
* As pointed out by Harriet Zuckerman, this view was not shared by Muller, who stood
further away from the group than the rest and thought that his own contributions had
not been fully recognized: see Zuckerman, 1977, pp. 141-143; see also Allen, 1978, pp.
201-208.
BIBLIOGRAPHY
Allen, G.E. (1978) Thomas Hunt Morgan: The Man and His Science. Princeton, NJ:
Princeton University Press.
Goldschmidt, R.B. (1950) "The Impact of Genetics Upon Science" in Genetics in the
Twentieth Century, Essays on the Progress of Genetics in Its First Fifty Years (Ed. L.C.
Dunn) pp. 1-23, New York, Macmillan.
Harrison, R.G. (1937) "Embryology and Its Relations," Science 85:369-374.
Jaffe, B. (1958) Men of Science in America: The Story of American Scientists Told
Through the Lives and Achievements of Twenty Outstanding Men from Earliest Colonial
Times to the Present Day. Rev. ed., 715 pp. Chapter 16. New York: Simon & Schuster.
Judson, H.F. (1979) The Eighth Day of Creation: The Makers of the Revolution in Biology.
New York: Simon & Schuster.
Kohler, R. E. (1994) Lords of the Fly: Drosophila Genetics and the Experimental Life.
Chicago: University of Chicago Press.
Morgan, T.H. et al. (1915) The Mechanism of Mendelian Heredity. New York: Holt
Rinehart & Winston. Reprinted. Johnson Reprint Corporation with an Introduction by
Garland E. Allen, 1978.
Morgan, T.H. (1934) Embryology and Genetics. New York: Columbia University Press.
Morgan, T.H. (1938) The Theory of the Gene. New Haven: Yale University Press
Shine, I., and Wrobel, S. (1976) Thomas Hunt Morgan: Pioneer of Genetics. Lexington:
University of Kentucky Press.
Sturtevant, A.H. (1959) Thomas Hunt Morgan: Biographical Memoirs. National
Academy of Sciences 33:295.
Sturtevant, A.H. (1965) Unpublished interview with G.E. Allen, Pasadena, Caltech
Archives, pg. 28.
Sturtevant, A.H. (1965) A History of Genetics. New York: Harper & Row.
Watson, J.D. (1968) The Double Helix: A Personal Account of the Discovery of the
Structure of DNA. New York: New American Library.
Zuckerman, Harriet (1977) Scientific Elite: Nobel Laureates in the United States. New
York: Free Press.
Tomado de:
http://www.nobelprize.org/nobel_prizes/medicine/laureates/1933/press.html
Discurso de presentación del Premio Nobel a Thomas H. Morgan por F. Henschen,
profesor del Royal Caroline Institute, el 10 de Diciembre de 1933.
Award Ceremony Speech
Presentation Speech by F. Henschen, member of the Staff of Professors of the Royal
Caroline Institute, on December 10, 1933.
Your Majesty, Your Royal Highnesses, Honourable Audience.
As long as human beings have existed they will have
observed children's resemblance to their parents, the
resemblance or non-resemblance of brothers and
sisters, and the appearance of characteristic qualities in
certain families and races. They will also early have
asked for an explanation of these circumstances, which
has produced a kind of primitive theory of heredity
chiefly on a speculative basis. This has been
characteristic of the theories of heredity right up to our
time, and as long as there existed no scientific analysis of
the hereditary conditions, the mechanism of fertilization
remained impenetrable mysticism.
Old Greek medicine and science took much interest in these questions. In Hippocrates,
the father of the healing art, you can find a theory of heredity that probably can be
traced back to primitive ideas. According to Hippocrates, inherited qualities, in some
way or other, must have been transmitted to the new individual from different parts
of the organisms of the father and the mother. Similar ideas of the transmission of
qualities from parents to children are to be found in other Greek scientists, and,
modified, also in Aristotle, the greatest biologist of the olden times.
Later on, this so-called transmission theory has been dominating. The only theory of
heredity that has perhaps rivalled it, is the so-called preformation theory, an old
scholastic idea that can be followed back to Augustine, the father of the Church. This
theory maintained that, by the creation of the first woman, all following generations
were also preformed in this first mother of ours. In modified form the preformation
theory dominated the biology of the eighteenth century. Nevertheless, the
transmission theory survived. Its last great representative was Darwin. He also seems
to have understood heredity as a transmission of the personal qualities of the parents
to the offspring through a kind of extract from the different organs of the body.
This conception, however, that is thus deeply rooted in the biology of past times and
that will still be adopted rather generally, is fundamentally false; it has been reserved
to the genetic researches of our time to prove this.
Modern hereditary researches are of a recent date, they are not yet seventy years old.
Their founder is the Augustine monk Gregor Mendel, Professor at Brünn, who
published (1866) his experiments on hybridization among plants, fundamental for
this whole science. In the same year, in Kentucky, the man was born, who became
Mendel's heir and founder of the school in heredity researches that has been called
higher Mendelism, the winner of this year's Nobel Prize in Physiology or Medicine,
Thomas Hunt Morgan.
Mendel's observations are of revolutionizing importance. As a matter of fact they
completely upset the older theories of heredity, although this was not at all
appreciated by his contemporaries. Mendel's discoveries usually are stated in two
heredity laws or better rules of heredity. The first of his rules, the cleaving rule, means
that if two different hereditary dispositions or hereditary factors (genes) for a certain
quality - for instance for size - are combined in one generation, they separate in the
following generation. If, for instance, a constantly tall race is crossed with a constantly
short race, the individuals of next generation become altogether medium-sized, or, if
the factor «tall» is dominant, exclusively tall. In the following generation, however, a
cleaving takes place, so that once more the size of the individuals becomes variable
according to certain numerical proportions, then of four descendants: one tall, two
medium-sized, and one short.
The second of Mendel's rules, the rule of free combinations, means that, when new
generations arise, the different hereditary factors can form new combinations
independent of each other. If, for instance, a tall, red-flowered plant is crossed with a
short, white-flowered one, the factors red and white can be inherited independent of
the factors large and small. The second generation then, besides tall red-flowered and
short white-flowered plants, produces short red-flowered and tall white-flowered
ones.
Mendel's immortal merit is his exact registration of the special qualities and
consequent following of their appearance from generation to generation. In this way
he discovered the relatively simple, recurrent, numerical proportions, which give us
the key to a true understanding of the course of heredity. The experimental genetics of
our century then has proved that, taken as a whole, these Mendel rules are applicable
to all many-celled organisms, to mosses and flowering plants, to insects, mollusks,
crabs, amphibia, birds, and mammals.
Mendel's rules, however, met with the same fate as many other great discoveries that
have been made before their time. Their significance was not understood, they fell
into oblivion, and after pater Mendel had died in 1884, nobody mentioned them any
more. Darwin apparently knew nothing about his great contemporary; otherwise he
could have made use of Mendel's works for his own researches, and the rediscovery of
Mendel's work was made only about 1900.
By that time, however, the qualifications for the application and perfection of Mendel's
theories were quite different from those of their first publication. The general
biological attitude had changed, and, above all, the knowledge of the cell and the cell
nucleus had made excellent progress. The mechanism of fertilization had been
discovered by Hertwig in 1875, and in the eighteen-eighties Weismann had asserted
the opinion that the nuclei of the sex cells must be the bearers of the hereditary
qualities. The indirect or mitotic cell division and the chromosomes - the strange,
threadlike, colourable structures that then appear - had been discovered by Schneider
in 1873 already. Only several decades later, however, was the meaning of the
remarkable cleaving, wandering, and fusion of these chromosomes during the
different phases of the cell division and the fertilization understood.
When, at last, Mendel's discoveries came to light, their significance was soon
perceived. Behind Mendel's rules there must be some relatively simple, cellular
mechanism for the exact distribution of the hereditary factors at the genesis of the
new individual. This mechanism was found just in the proportion of chromosomes in
the sex cells before and after the fertilization. The opinion that the chromosomes are
the real bearers of heredity was first clearly pronounced by Sutton in 1903, and by
Boveri in 1904. This opinion was enthusiastically received by the students of the cell.
Only by this discovery organic life got the unity, the continuity that human thought
demands and that is more real and more provable than the hypothetic common
descent of Darwinism.
The further development of the chromosome theory during the first decade of this
century may here be skipped. However, the soil was well prepared when, in 1910, the
American zoologist Thomas Hunt Morgan began his researches in heredity. These
soon led him to the great discoveries regarding the functions of the chromosomes as
the bearers of heredity that have now been rewarded with the Nobel Prize for
Medicine in 1933.
Morgan's greatness and the explanation of his astonishing success is partly to be
found in the fact that, from the beginning, he has understood to join two important
methods in hereditary research, the statistic-genetic method adopted by Mendel, and
the microscopic method, and that he has always looked for an answer to the question:
which microscopic processes in cells and chromosomes result in the phenomenons
appearing at the crossings?
Another cause for Morgan's success is no doubt to be found in the ingenious choice of
object for his experiments. From the beginning Morgan chose the so-called banana-fly,
Drosophila melanogaster, which has proved superior to all other genetic objects
known so far. This animal can easily be kept alive in laboratories, it can well endure
the experiments that must be made. It propagates all the year round without intervals.
Thus a new generation can be had about every twelfth day or at least 30 generations a
year. The female lays about 1,000 eggs, males and females can easily be distinguished
from each other, and the number of chromosomes in this animal is only four. This
fortunate choice made it possible to Morgan to overtake other prominent genetical
scientists, who had begun earlier but employed plants or less suitable animals as
experimental objects.
Finally, few have like Morgan had the power of assembling around them a staff of very
prominent pupils and co-operators, who have carried out his ideas with enthusiasm.
This explains to a large extent the extraordinarily rapid development of his theories.
His pupils Sturtevant, Muller, Bridges, and many others stand beside him with honour
and have a substantial share in his success. With perfect justice we speak about the
Morgan school, and it is often difficult to distinguish what is Morgan's work and what
is that of his associates. But nobody has doubted that Morgan is the ingenious leader.
As Mendelism can be summed up in Mendel's two rules, Morganism, at least to a
certain extent, can be expressed in laws or rules. The Morgan school usually speaks of
four rules, the combination rule, the rule of the limited number of the combination
groups, the crossing-over rule, and the rule of the linear arrangement of the genes in
the chromosomes. These rules complete the Mendel rules in an extraordinarily
important way. They are all inextricably connected, and form together a close
biological unity.
It is true that Morgan's combination rule, according to which certain hereditary
dispositions are more or less firmly combined, limits to a large degree Mendel's
second rule that, at the formation of new hereditary substances, the genes may be
freely combined. It is completed by the rule of the limited number of the combination
groups, which has turned out to be corresponding to the number of chromosomes. On
the other hand, the combination rule is confined by the strange phenomenon that
Morgan calls crossing-over or the exchange of genes, which he imagines as a real
exchange of parts between the chromosomes. This crossing-over theory has met with
much resistance. During the last few years, however, it has got a firm support through
direct microscopic observations. Also the theory of the linear arrangement of the
hereditary factors seemed in the beginning a fantastic speculation, and the publication
of Morgan's so-called genetic chromosome map, upon which the different hereditary
factors are checked in the chromosomes like beads in a necklace, was greeted with
justified scepticism. The fact was that Morgan had arrived at these sensational
conclusions by statistic analysis of his Drosophila crossings and not by direct
examination of the chromosomes, which, besides, is possible only in exceptional cases.
But also on this point later researches have acknowledged him to be in the right, and
nowadays also other genetic scientists admit that the theory of the localization of the
hereditary factors within the chromosomes is not an abstract way of thinking but
corresponds to a stereometric reality.
The results of the Morgan school are daring, even fantastic, they are of a greatness
that puts most other biological discoveries into the shade. Who could dream some ten
years ago that science would be able to penetrate the problems of heredity in that
way, and find the mechanism that lies behind the crossing results of plants and
animals; that it would be possible to localize in these chromosomes, which are so
small that they must be measured by the millesimal millimetre, hundreds of
hereditary factors, which we must imagine as corresponding to infinitesimal
corpuscular elements. And this localization Morgan had found in a statistic way! A
German scientist has appropriately compared this to the astronomical calculation of
celestial bodies still unseen but later on found by the tube - but he adds: Morgan's
predictions exceed this by far, because they mean something principally new,
something that has not been observed before.
Morgan's researches chiefly occupy themselves with the family of Drosophila, and
perhaps it may seem strange that his discoveries have been rewarded with the Nobel
Prize for Medicine, which is to be bestowed on the man who «has done the greatest
service to mankind» and «has made the most important discoveries in the field of
physiology or medicine». To this may first be alleged that numerous later
examinations of other genetic objects, of lower and higher plants and animals, have
given evidence of the fact that, as a principle, Morgan's rules are applicable to all
many-celled organisms.
Further, comparative biological research has for a long time shown a far-extending
fundamental correspondence between man and other beings. We can therefore
consider it as a matter of course that also such an elementary function of the cell as
the transmission of hereditary dispositions is similar, that, in other words, Nature
uses the same mechanism with man as with other beings to preserve species, and that
Mendel's and Morgan's rules thus are applicable also to man.
Human hereditary researches have already made great use of Morgan's investigations.
Without them modern human genetics and also human eugenics would be impractical
- it may be that eugenics still chiefly remain a future goal. Mendel's and Morgan's
discoveries are simply fundamental and decisive for the investigation and
understanding of the hereditary diseases of man. And considering the present attitude
of medicine and the dominating place of the constitutional researches, the role of the
inner, hereditary factors as to health and disease appears in a still clearer light. For
the general understanding of maladies, for prophylactic medicine, and for the
treatment of diseases, hereditary research thus gains still greater importance.
Mr. Steinhardt. The Caroline Institute regrets very much that Professor Morgan is not
able to be here today in person. I beg Your Excellency, as the official representative of
the United States of America, to accept the Nobel Prize for Professor Morgan. May I
also ask Your Excellency, in forwarding the prize to him, to convey with it the
admiring congratulations of our Institute.
From Les Prix Nobel en 1933, Editor Carl Gustaf Santesson, [Nobel Foundation],
Stockholm, 1934