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Excerpt of 1906 letter from W. Spillman to the American Breeders Association. The letter summarizes "recent" discoveries in genetics. Boxed text talks about the "theoretical" nature of genes.
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Hugo de Vries, 1912.
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A meeting between Hugo de Vries and Thomas Hunt Morgan.
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Hugo de Vries.
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Hugo de Vries and a group of scientists examining varieties of evening primrose.
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Carl Correns.
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"With best wishes, Carl Correns," around 1925.
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Erich von Tschermak-Seysenegg, 1941.
Audio Glossary
Cell, Chromosome, NucleusVideo Interviews
Professor of History Robert Olby teaches at the University of Pittsburgh, and has written several books on the history of genetics, including Origins of Mendelism and The Path to the Double Helix.
Clip 1 (1:00)
Mendel's rediscovery: two of the three rediscoverers had read Mendel's paper.
Clip 2 (0:40)
The need for the "prepared mind" in interpreting data: the failure of Hugo de Vries to see ratios.
Clip 3 (1:10)
The danger of invoking unobservable entities in science.
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Hugo de Vries, Carl Correns and Erich von Tschermak-Seysenegg were the three scientists who rediscovered Mendel's laws in 1900. They were all working independently on different plant hybrids, and came to the same conclusions about inheritance as Mendel. Robert Hooke was one of the first scientists to describe a cell. Theodor Schwann redefined the cell as a living unit.
HUGO DE VRIES (1848-1935)
Hugo de Vries was born in Haarlem, Netherlands. He was a Professor of Botany at the University of Amsterdam when he began his genetic experiments with plants in 1880. He completed most of his hybridization experiments without knowing about Mendel's work. Based on his own results, de Vries drew the same conclusions as Mendel. De Vries published his work in 1900, first in French then in German. In the French report there was no mention of Mendel, but this was amended by de Vries in the German paper. It is possible that de Vries read Mendel's paper before he published his own, and included Mendel's name in the later printing when he realized that other people also knew about Mendel's work. De Vries may have thought that his own conclusions were superior to Mendel's. De Vries was also a strong proponent of the idea of discontinuous variations. De Vries believed species evolve from other species through sudden, large changes of character traits. De Vries based this "theory of mutation" on work he did using Oenothera lamarckiana - the evening primrose. He observed that the original plant would occasionally have offspring with significant phenotypic differences such as leaf shape and plant sizes. Some of the offspring would pass the new "sport" (mutation) to their progeny; these de Vries designated as new species. It is now known that de Vries had the right idea, but for the wrong reasons. Most of the variants that de Vries isolated from Oenothera lamarckiana were due to aberrant chromosomal segregations, and not to mutations associated with specific genes. CARL ERICH CORRENS (1864-1933)
Carl Correns was born in Münich, Germany, and was orphaned at an early age. He was raised by his aunt in Switzerland. In 1885, he entered the University of Münich to study botany. Carl Nägeli, the botanist to whom Mendel wrote to about his pea plant experiments, was no longer lecturing at Münich. Nägeli, however, knew Correns' parents and took an interest in him. Nägeli was the one who encouraged Correns' interest in botany and advised Correns on his thesis subject. Nägeli and Correns' connection was more than just scientific; Correns eventually married Nägeli's grandniece. Correns was a tutor at the University of Tübingen when he began to experiment with trait inheritance in plants in 1892. Correns already knew about some of Mendel's hawkweed plant experiments from Nägeli. Nägeli, however, never talked about Mendel's key pea plant results, so Correns was initially unaware of Mendel's laws of heredity. However, by 1900, when Correns submitted his own results for publication, the paper was called: G. Mendel's Law Concerning the Behavior of the Progeny of Racial Hybrids. Correns and de Vries were the ones who most clearly "redefined" Mendel's laws. Mendel, in his paper, spoke about the "law of combination of different characters" and talked about "the law of independent assortment." Mendel implied that the segregation of factors occurred in the production of sex cells. Correns (with credit to de Vries) restated Mendel's results, giving us Mendel's law of segregation and Mendel's law of independent assortment. Correns was active in genetic research in Germany, and was modest enough to never have a problem with scientific credit or recognition. He believed that his other work was more important, and the rediscovery of Mendel's laws only helped him with his other work. Correns was supposedly indignant that Hugo de Vries did not mention Gregor Mendel in the first printing of de Vries' paper. Credit should be given where due. In 1913, Correns became the first director of the newly founded Kaiser Wihelm Institut für Biologie in Berlin-Dahlem. Unfortunately, most of his work was unpublished and destroyed when Berlin was bombed in 1945. ERICH VON TSCHERMAK-SEYSENEGG (1871-1962)
Erich von Tschermak-Seysenegg was born in Vienna, Austria. His father was a well-known mineralogist, and his maternal grandfather was the famous botanist, Eduard Fenzl, who taught Gregor Mendel at one point. He studied agriculture at the University of Vienna, and worked on a farm to gain practical agricultural experience. Tschermak graduated with a doctorate from the Halle-Wittenberg University. In 1898, he started doing plant breeding experiments using peas, and by 1900, he had written up his results. Tschermak, like de Vries and Correns, independently derived "Mendelian" laws of inheritance from his plant experiments. Because he was younger, and not as established in the scientific community, Tschermak was worried about the acceptance of his paper given those of de Vries' and Correns'. However, he was able to rush his paper to press, and was accorded his share of attention as one of the rediscoverers of Mendel's laws. Tschermak was a plant breeder, and his hybridization experiments were done with the idea of improving crops using the laws of heredity. He did most of the work himself, and produced high-yielding food crops such as wheat, barley, and oats. In 1903, Tschermak was appointed associate professor at the University of Agricultural Sciences in Vienna, and later became a full professor. He was a major influence in agriculture and plant breeding in Austria. ROBERT HOOKE (1635-1703)Robert Hooke was born in Freshwater, England, on the Isle of Wight. Hooke was educated at Westminster, and in 1658, attended Christ Church at Oxford University. Presumably he paid for his education with some money he inherited on the death of his father. At Oxford, he met Robert Boyle who became his patron. Boyle hired Hooke to work in his laboratory, and also sponsored Hooke for membership in the Royal Society of London. The Royal Society was started for the purpose of discussion and promotion of subjects in natural sciences. Members gathered on a regular basis, and it was at one of these meetings in 1663 that Hooke showed them the power of his newly designed microscope. In 1665, Hooke published Micrographia which contained drawings and descriptions of all sorts of material he examined under his microscope including the famous cork cells. In the same year, Hooke became professor of geometry at Gresham College, a post he occupied until his death. Hooke was a practical and theoretical genius in almost all fields of science. Long before Darwin, Hooke recognized that fossils were remains of ancient life, and were historical life records. He was mechanically adept, and invented and improved many useful instruments besides the microscope. He invented the conical pendulum, spiral springs used in watches, the quadrant, the Gregorian telescope and the air pump used by Boyle for his experiments on gases. Hooke also designed (though never built) the steam engine, and described a working telegraph system. As a mathematician, Hooke worked on the problem of gravity and planetary orbits. He fought with Sir Isaac Newton over the origin of the inverse square law of gravity - Hooke accused Newton of having stolen the idea from him and often engaged him in very public and very loud debates. After the Great Fire of 1666, Hooke was chosen to design New Bethlehem Hospital in London, better known as Bedlam. He also designed a number of private houses in London. No known portrait of Hooke exists. He was described as a lean, ugly man, which may be a reason why he never sat for his portrait. Hooke died in London in 1703 at the age of 68. THEODOR SCHWANN (1810-1882)
Theodor Schwann was born in Neuss, Germany. He studied medicine in Berlin, and after graduation went on to do an assistantship in anatomy. In 1838, Schwann and Matthias Jakob Schleiden (1804-1881) developed the "cell theory." Schwann went on and published his monograph Microscopic Researches into Accordance in the Structure and Growth of Animals and Plants in 1839. In the monograph, Schwann identified the common features of all cells - plants and animals, and he illustrated many different cell types. Although Schwann did change the definition of cell by stressing the internal cellular components, he believed incorrectly that cells could arise from assembly of cellular fluids. In 1839, Schwann was appointed Professor of Anatomy at the University of Louvain. In 1848 he moved to Liège where he taught physiology and comparative anatomy. |
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LinksHistory of the Light MicroscopeThis site looks at the evolution of the light microscope. There is a section on Robert Hooke and the microscope he used in Microscopes of the 17th Century. Mendel WebThis is site where you can get a lot of information about Gregor Mendel, his life and scientific achievements. Read how Mendel and his work have been viewed in this century in Dr. Jan Sapp's essay The Nine Lives of Gregor Mendel. Bibliography
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