Hugo de Vries

Experimental Work with Sachs

Pursuing physiological studies at Leiden, de Vries earned his doctorate in plant physiology in 1870, but felt stifled by the university, where conditions for experimental work were crude and where there was open hostility to Darwinism. He therefore decided to continue his education in Germany, first at Heidelberg (1870) and then at Würzburg (1871) with Sachs. Sachs took a great interest in de Vries' career, helping him refine his experimental techniques and nominating him for several important posts over the next few years. Sachs was a strong proponent of experimentation. Under his guidance de Vries began a series of detailed studies of osmosis, plasmolysis, and the effects of salt solutions on plant cells. He carried out these experiments at Würzburg, then at Amsterdam while teaching in a gymnasium (1871-1877), and finally at the University of Amsterdam where he was appointed lecturer in plant physiology in 1877 and professor in 1881; he remained at Amsterdam until compulsory retirement in 1918, when he moved to the small village of Lunteren.

In the late 1880s de Vries shifted from experimental work in plant physiology to the study of heredity. His first major publication on this subject was Intracellular Pangenesis in 1889, a critical review of the hereditary theories of Darwin, Herbert Spencer, August Weismann, and Carl von Nägeli. All of these writers had proposed some form of particulate theory of heredity. De Vries added to the list one of his own, the theory of "pangenes" (a term he borrowed from Darwin), unitary particles representing individual traits of an organism and manifesting themselves independently in the adult. De Vries considered the pangene a material unit that could combine and recombine in successive generations much like atoms in the formation of molecules. Although de Vries' hypothesis cannot be considered a forerunner of the Mendelian-chromosome theory that emerged in the 20th century, it was an elegant example of the sorts of theories of heredity and evolution that dominated much of later 19th-century biological thought.

As a result of his physiological training, de Vries was interested in studying heredity and evolution from a quantitative and experimental, rather than a purely theoretical, point of view. In the early to mid 1890s, he learned of the statistical work on variation being developed by Francis Galton in England. A strict Darwinian, Galton measured traits in animal populations and showed that they generally graphed as a smooth or "normal curve" of distribution. De Vries' studies showed that such curves also existed for many traits in plants. But he also found that many traits showed a bimodal or discontinuous distribution, suggesting that populations are often mixtures of varieties, or races, that can be separated from one another by selection. Crossing several closely related races of poppy, xenia, and other species that differed from one another by only one or a few traits, de Vries arrived independently (by 1896) at what is now known as Mendel's law of segregation. In 1900 he accidently came across and read Mendel's original paper of 1866 and incorporated a discussion of Mendel's results in his own work on the poppy, published in 1900. This publication appears to have triggered both Carl Correns and Erich von Tschermak-Seysengg to read Mendel's work and recognize its importance. The result was to bring to the attention of the scientific world the work of Gregor Mendel which was soon to lay the foundation for modern genetics.

Working Out the Mutation Theory

It was for his work on the mutation theory, however, that de Vries ultimately became most well-known. In 1886 near Hilversum, outside of Amsterdam, de Vries noted what appeared to be several species of the evening primrose, Oenothera lamarckiana, growing side-by-side. Taking seeds from these plants and growing them in his experimental garden, de Vries found they produced many variant forms which he classified as new and distinct species. These suddenly-appearing variations de Vries called mutations, and in his The Mutation Theory (1901-1903) he suggested that evolution might occur more frequently by these large-scale jumps than Darwin's natural selection acting on slight individual variations. There were, de Vries noted, several types of mutations that occurred in plants: progressive (introducing a wholly new character, and usually making the plant a new species); retrogressive (loss of a trait); and degressive (activation of a trait long-latent in the species). While de Vries saw retrogressive and degressive mutations as following Mendel's laws (progressive mutations did not), he made little of the point. His major interest lay less in the problem of heredity and more in that of the origin of species.

De Vries' mutation theory was enthusiastically received by many investigators at the time as meeting many of the difficulties they saw in the Darwinian theory: lack of sufficient geological time for the slow and haphazard process of natural selection to produce new species; the problem of new traits being swamped or blended out by backcrossing with the parents; and the reliance of Darwinians on the heritability of slight, individual (as opposed to largescale) variations as the raw material on which selection could act. De Vries travelled widely lecturing on the mutation theory, going to the United States in 1904, 1906, and again in 1916, where he stimulated many investigators to seek in other organisms, including animals, large-scale mutations of the sort he had found in Oenothera. While no such mutations were forthcoming, de Vries' work did stimulate much interest in the experimental study of evolution, as investigators sought ways to produce mutations artificially and to detect their presence through experimental breeding. One result of de Vries' influence was that in 1908 Thomas Hunt Morgan at Columbia University began to search for mutations in the fruit fly Drosophila melanogaster, an organism whose favorable breeding characteristics were to become a major focus for experimental genetics in the 20th century.

Among his many honors, de Vries was the recipient of 11 honorary degrees and became a corresponding member of many foreign academies of science. His world-wide esteem was reflected in invitations to give the major lectures at the opening of the Station for Experimental Study of Evolution at Cold Spring Harbor, Long Island (1904), and at the dedication of Rice Institute in Houston, Texas (1916).

As influential as it was in his own day, de Vries' mutation theory did not pass the test of time. Between 1907 and 1915 various cytogeneticists showed that heredity in Oenothera involved a number of unusual chromosomal phenomena (polyploidy, or increased numbers of chromosomes; two groups of chromosomes attached end-to-end, each transmitted as a whole from parent to offspring) that gave only the illusion of new species. In reality the mutants of Oenothera were explicable not by de Vries' pet mutation theory but by the very Mendelian theory de Vries had helped to recover. Eventually, by the early 1920s, the mutation theory was abandoned as an explanation for origin of species. (The modern term "mutation" refers only to small, discrete variations in particular traits, and thus has a much different meaning from de Vries' usage.)

Further Reading

A biographical sketch of Hugo de Vries written by Peter van der Pas for the Dictionary of Scientific Biography includes a lengthy bibliography. For the reception of de Vries' work, see Garland E. Allen, "Hugo de Vries and the reception of the 'mutation theory'," Journal of the History of Biology (1969). For the relationship between de Vries and evolutionary problems, see: Lindley Darden, "Reasoning in scientific change: Charles Darwin, Hugo de Vries, and the discovery of segregation," in Studies in History and Philosophy of Science (1976) and Peter van der Pas, "Correspondence of Hugo de Vries and Charles Darwin," Janus (1970). De Vries' role in modern genetics is discussed in J. Heimans, "Hugo de Vries and the gene concept," in Human Implications of Scientific Advance: Proceedings of the XV^e International Congress of History of Science, E. G. Forbes, editor (Edinburgh, 1978); in Malcolm Kottler, "Hugo de Vries and the rediscovery of Mendel's laws," Annals of Science (1979); and in Peter van der Pas, "Hugo de Vries and Gregor Mendel," Folia Mendeliana (1976). □