Mendel, Gregor

Austrian Natural Scientist 1822-1884

Gregor Mendel elucidated the theory of particulate inheritance, which forms the basis of the current understanding of genes as the hereditary material. Born in Heinzendorf, Austria, in 1822, Johann Gregor Mendel was the fourth of five children in a family of farmers. He attended the primary school in a neighboring village, which taught elementary subjects as well as the natural sciences. Mendel showed superior abilities, and in 1833, at the advice of his teacher, his parents sent him to the secondary school in Leipnik, then to the gymnasium in Troppau. There he attempted to support himself by private tutoring, but his lack of the necessary financial support made the years that Mendel spent in school extremely stressful for him. His younger sister gave him part of her dowry and, in 1840, he enrolled in the University of Olmütz, where he studied physics, philosophy, and mathematics. In 1843 he was admitted into the Augustinian monastery in Brno, where he stayed for almost two decades. Originally, Mendel was not interested in religious life, but joining the monastery freed him from the financial concerns that plagued him and allowed him to pursue his interests in the natural sciences.

Under the leadership of its abbot, F. C. Napp (1792-1867), the monastery in Brno integrated higher learning and agriculture by arranging for monks to teach natural sciences at the Philosophical Institute. Napp encouraged Matthew Klácel to conduct investigations of variation and heredity on the garden's plants. Klácel, a philosopher by training, integrated natural history and Hegelian philosophy to formulate a theory of gradual development. This work eventually led to his dismissal, and he immigrated to the United States. Mendel was put in charge of the garden after Klácel's departure.

From 1844 through 1848 Mendel took theological training as well as agricultural courses at the Philosophical Institute, where he learned about artificial pollination as a method for plant improvement. After he finished his theological studies, Mendel served a brief and unsuccessful stint as parish chaplain before he was sent to a grammar school in southern Moravia as a substitute teacher. His success as a teacher qualified him for the university examination for teachers of natural sciences, which he failed because of his lack of formal education in zoology and geology. To prepare himself to retake the test, he went to the University of Vienna, where he enrolled in courses in various natural sciences and was introduced to botanical experimentation. After completing his university training he returned to Brno and was appointed substitute teacher of physics and natural history at the Brno technical school.

Mendel was an excellent teacher, and he often taught large classes. In 1856 he began botanical experiments with peas (Pisum), using artificial pollination to create hybrids. Hoping to continue his education, he once again took the university examination, but failed and suffered an emotional and physical breakdown. His second failure spelled the end of his career as a student, but he remained a substitute teacher until 1868, when he was elected abbot of the monastery. Mendel stayed in Brno, serving the monastery, performing botanical experiments, and collecting meteorological information until he died of kidney failure in 1884. At the time of his death, he was well known for his liberal views and his conflict with secular authorities over the setting aside of monastery land; at this time, only the local fruit growers knew him for his botanical research.

Experiments on Inheritance

While his contemporaries knew little of his scientific work, Mendel's historical significance lies almost entirely in his experimental work with the hybridization of plants and his theory of inheritance. Beginning in 1856 and continuing through 1863, Mendel cultivated nearly thirty thousand plants and recorded their physical characteristics. Beginning with a hypothesis about the relationship between characteristics in parents and off-spring, Mendel formulated an experimental program.

Mendel believed that heredity was particulate, that attributes were passed from parents to offspring as complete characters. His notions of heredity were contrary to the belief in blending inheritance, which was generally accepted at the time and explained the attributes of an organism as a blended combination of its parents' characters. Instead of viewing an organism's individual characteristics as composites of its predecessors, Mendel asserted that organisms inherited entire characters from either one or the other parent. To test his theory, he chose seven plant and seed characteristics, such as the shape of the seed or the color of the flower, and traced the inheritance of the characters through several generations of pea plants.

As he crossed thousands of pea plants and recorded the seven characteristics, Mendel found that certain traits were passed from parent to offspring in a lawlike fashion. Just as he had hypothesized, certain traits regularly appeared when he crossed plants with different combinations of characteristics. He used the term "dominant" in reference to those traits that were passed from the parent to the offspring and the term "recessive" in reference to those traits that were exhibited in at least one of the parents, but not in its offspring. Mendel denoted plants with dominant traits by recording two capital letters, such as AA, and those that expressed recessive traits with lower case letters, like aa. In the first generation of offspring from crosses of AA with aa, dominant traits always appeared and recessive traits never appeared.

Mendel's system of denoting dominant and recessive traits with two letters allowed him to trace dominant and recessive characters through successive generations. The crossing of AA with aa would result in the production of individuals with traits represented by Aa, with the dominant trait always appearing, but not the recessive trait. By crossing two Aa individuals, Mendel found that the dominant trait appeared three times for every one time that the recessive trait appeared. Mendel explained that the crossing of two Aa individuals resulted in the production of the following combinations:

AA Aa Aa aa

Because the dominant trait always decided the characteristic, any organism with at least one A would express the dominant trait. Recessive characteristics would appear only in those individuals with aa.

Mendel's 1866 "Versuche über Pflanzenhybriden" (Attempts at Plant Hybridization) presented his entire theory of inheritance and has become one of the most significant papers in the history of biology. He explained that his results "were not easily compatible with contemporary scientific knowledge" and, as such, "publication of one such isolated experiment was doubly dangerous, dangerous for the experimenter and for the cause he represented." In an attempt to bolster his case, Mendel experimented on several other plants and then with animals. However, after 1866 he published only one more short article on the subject.

Rediscovery of Mendel's Work

Mendel's painstaking experimental work on plant hybridization and heredity sat virtually unnoticed for thirty-five years before three natural scientists simultaneously rediscovered it at the turn of the twentieth century. His 1865 paper, presented at the Natural Sciences Society of Brno and published in the Society's Verhandlungen in 1866, received little notice from his contemporaries. However, in 1900 Carl Correns, Erich von Tschermak, and Hugo DeVries, each working independently, found Mendel's paper while they were each in the process of completing similar experiments. In the hands of a new generation of natural scientists, Mendel's work was immediately and widely accepted, and he was touted as the epitome of a scientist.

Mendelism, as his work was called, was often posited in opposition with the Darwinian theory of natural selection. Many early twentieth-century Mendelians and Darwinians believed that the two theories were incompatible with one another, in part because of Darwin's reliance on the theory of pangenesis and because contemporary biologists, who also viewed Darwinism in conflict with DeVries's mutationism, associated Mendel's work with mutationism.

Despite the debates over the relationship between Mendelism and Darwinism, Mendel's work immediately received widespread support, and it served as the basis for work in genetics as well as plant and animal breeding. Beginning around 1900, Mendelism also provided a substantial boost to the growing science of eugenics, the genetic improvement of humans by encouraging "high-quality" individuals to have children while discouraging "low-quality" people from reproducing. By scientifically explaining inheritance, Mendelism bolstered the eugenicists' claim that "good begets good and bad begets bad." Later geneticists distanced themselves from eugenics by arguing that, while Mendelism easily explained simple traits like eye color or blood type, it did not apply to more complicated traits like intelligence or industriousness.

Beginning in the late 1930s, yet another generation of natural scientists reinterpreted Mendelism and Darwinism, and they concluded that they were mutually reinforcing scientific theories. R. A. Fisher, Sewall Wright, J. B. S. Haldane, and other so-called synthesis biologists argued that Mendelism provided the explanation for one facet of evolution, inheritance, while Darwinism explained another, selection. Viewed in this light, Mendel's work complemented Darwin's theory of natural selection, and the two have served as the principal basis for modern biological thought since the mid-twentieth century.

Mark A. Largent

Bibliography

DeVries, Hugo, Carl Correns, and Armin von Tschermak. The Birth of Genetics. Brooklyn, NY: Brooklyn Botanic Garden, 1950.

Iltis, Hugo, Eden Paul, and Cedar Paul. Life of Mendel. London: G. Allen & Unwin, 1932.

Kruta, V., and V. Orel. "Johann Gregor Mendel." In Dictionary of Scientific Biography, Vol. 9. New York: Charles Scribner's Sons, 1974.

Olby, Robert. The Origins of Mendelism. New York: Schocken Books, 1966.