Johannsen, Wilhelm Ludvig

(b. Copen- hagen, Denmark, 3 February 1857; d. Copenhagen, 11 November 1927)

biology.

Johannsen, one of the founders of the science of genetics, was the son of a Danish army officer, Otto Julius Georg Johannsen, and the former Anna Margrethe Dorothea Ebbesen. His father’s family included many civil servants; the interest of his mother and maternal grandmother in German culture influenced Johannsen’s childhood experience. He attended a good elementary school in Copenhagen, but his father’s means did not permit him to enter the university, so in 1872 he was apprenticed to a pharmacist. He worked in pharmacies in Denmark, where he taught himself chemistry, and in Germany, where he became interested in botany.

Johannsen returned to Denmark in 1879, passed the pharmacist’s examination, and continued his studies in botany and chemistry. In 1881 he became assistant in the department of chemistry of the newly established Carlsberg laboratory. His chief was the chemist Johan Kjeldal, who developed the method for determining nitrogen in organic substances. Here he was given freedom to work independently. His research centered on the metabolic processes connected with ripening, dormancy, and germination in plants, especially in seeds, tubers, and buds. These were the formative years of Johannsen’s scientific life, both with respect to the problems which he chose and stated with great clarity and especially to the exact quantitative methods which he sought and used. Essentially self- taught, Johannsen was widely read in several languages, philosophy, aesthetics, and belles letters as well as in science.

In 1887 Johannsen resigned his post at the Carlsberg laboratory but with the aid of stipends continued some of his own research there and discovered a method of breaking the dormancy of winter buds. (First demonstrated in 1893, this work is described in Das Aether- Verfahren.) He traveled to Zurich, Darmstadt, and Tü bingen for further work in plant physiology. In 1892 he became lecturer, and in 1903 professor, of botany and plant physiology at the Copenhagen Agricultural College.

In 1905 Johannsen was appointed professor of plant physiology at the University of Copenhagen and in 1917 became rector of the university, although he had no university education. His scientific eminence was recognized by the award of several honorary degrees and membership in the Royal Danish Academy of Science and in academies and learned societies outside Denmark.

Johannsen was an interesting figure in many ways; as theorist and analytical logician, as discoverer of a major concept in genetics ( “pure line theory”), and as critic, clarifier, popularizer, and historian of scientific ideas. His claim on the attention of historians of science has steadily increased since his death, even though, with a few exceptions, his publications were written in Danish. The reason may be that genetics, which in its formative stages (1900- 1915) was strongly influenced by Johannsen, has grown in the direction he emphasized. His main concern was with the analysis of the heredity of normal characters which vary quantitatively, such as size, fertility, and degree of response to environmental factors. these provide much of the variety upon which natural selection acts and with which breeders of useful plants and animals are mainly concerned. Through the development of population genetics, the genetic structure of populations, as Johannsen was one of the first to recognize, occupies an increasingly important place in evolutionary biology.

Moreover, Johannsen’s view of the unit of heredity, to which he first gave the name “gene” (1909), has survived the changes brought about by the chromosomes and then more precisely in the structure of the nucleic acids. He conceived of genes as symbols: Rechnungseinheiten, units of calculations or accounting.

Proof of the existence of such elements was of course due to Mendel (1866), but it was Johannsen who first stated clearly the fundamental distinction between the symbolic view of the hereditary constitution of the organism—its genotype, consisting of the totality of its genes—and its phenotype, how it appears and acts. the latter, as Johannsen pointed out, is the observed reality, representing the responses of the organism, as determined by its genotype, to the conditions encountered by the individual during its life history. Introduced by Johannsen in 1909, these terms embody concepts that remain essential in the interpretation of processes of heredity and of evolution.

Johannsen began his study of variability in relation to heredity in the early 1890’s. He was strongly influenced by Darwin’s work and especially by that of Francis Galton, whose “Theory of Heredity” (Journal of the Anthropological Institute of Great Britain and Ireland [1876]) suggested both ideas and quantitytive, statistical methods which Johannsen improved. Galton had derived his first so- called law of regression to the mean from the self- fertilizing sweet pea plant. Johannsen chose the common princess bean and discovered, as Galton had, that the seeds of the offspring have the same average weight as the seeds of the parent plant, in spite of selection for higher or for lower weight.

This seemed a remarkable discovery to Johannsen, and he dedicated his paper of 1903, “ü ber Eriblichkeit in Populationen und in reinen Linien,” to “the creator of the exact science of heredity, Francis Galton F.R.S. in respect and gratitude.” Yet Johannsen had shown that Galton’s “law of regression” was wrong when applied as Galton had done—to impure or mixed populations. He proved that selection was ineffective—that is, regression to parental averages was complete—only in the offspring derived by self- fertilization from a single parent, as in peas, beans, and other “selfers” The offspring and descendants from such a plant Johannsen referred to as a “pure line.” His theory was that the offspring of a pure line were genetically identical and that fluctuating variability among such offspring was due to effects of chance and of environmental factors. These effects were not heritable and hence were not subject to the action of selection, either natural or artificial. The differences between the different pure lines composing a “population” were inherited and had arisen by mutation, a process then recently invoked (1900) by the Dutch botanist Hugo de Varies as the source of inherited variations which led to the origin of new “elementary species. “Johannsen was the first to attribute to mutation the origin of the small differences in the continuous kind of variability characteristic of normal heredity. His proof of the existence of two kinds of variability—heritable and non heritable—eliminated the need felt by Darwin and other nineteenth- century naturalists for invoking the inheritance of acquired characters as an evolutionary process.

Johannsen had first set forth his views on the nature of the evolitionary process, including the part played by discontinuous variation (mutation) in the little book Om arvelighed og variabiliet ( “On Heredity and Variation“), issued by the student organization of the Copenhagen Agricultural College in 1896. It proved to contain a preview, not only of the direction of Johannsen’s own future work but also of the new attitudes toward Darwin’s theory of the mechanism of evolution which arose after the elaboration of de Vries’s mutation theory and the rediscovery of Mendel’s theory of heredity beginning in 1900. Johannsen’s main ideas about heredity, including the assumption of particulate elements, antedated there discovery of Mendel’s work, of which Johannsen first took public notice on 27 November 1903. Johannsen was clearly prepared to appreciate the significance of Mendel’s theory and immediately set about incorporating it into his theory of the evolutionary process. This book was enlarged and reissued in 1905 as Arvelighedslaerens elementer ( “The Elements of Heredity”). Greatly expanded and re written by Johnnsen in German, it became in 1909 the first and most influential textbook of genetics on the European continent. About half of the book was devoted to the mathematical and statistical methods needed in the analysis of the quantitative data arising from experiments in genetics. This was what “exakten” in the title meant, not pretensions on the part of a new biology but, rather, delimitation of that part of a heterogeneous field which could be dealt with by quantitative methods applied to verifiable facts. In this book Johannsen defind the basic concepts of a new science—“gene,” “genotype,” “phenotype”—and forecast the effects to be expected from it upon the central problem of biology, that of the mechanism of organic evolution. The Elemente appeared in revised editions, the third (and last) in 1926. Many European biologists owed to it their introduction to genetics.

After his “pure line” work, Johannsen gave up experimentation. His work as critic and historian of science showed the same lively mind of a free- lancer in science as his scientific contributions. Falske Analogier (1914) revealed that the kind of logic which Johannsen introduced into genetics was in his hands a tool in a wider crusade to banish obscurantism, teleology, and mysticism from biology. In one chapter he analyzed Henri Bergson’s é volution cré atrice as “a whole system of false analogies” based on “unverified speculation” and concluded: “It is a pure waste of time to lose oneself in such an author’s ‘ positive’ views; they are just not worth a bean” (pp. 102- 103). (Beans were Johannsen’s chief research material.)

His 1923 book Aravelighed i historisk og experimentel Belysning ( “Heredity in the Light of History and Experimental Study”), although it appeared only in Danish, went through four editions. It is a lively account of ideas on heredity from the Greeks to T. H. Morgan, author of The Theory of the Gene, of whose views Johannsen had been sharply critical.

Johannsen’s place in the history of biology may come to be seen as a bridge over which nineteenth- century ideas of heredity and evolution passed to be incorporated, after critical purging, into modern genetics and evolutionary biology.

BIBLIOGRAPHY

I. Original Works. Johannsen’s chief writings are Laerebog i plantefisiologi med henblik paa plantedyrkningen (Copenhagen, 1892); Om arvelighed og variabilitet (Copenhagen, 1896), enl. as Arvelighedslaerens elementer (Copenhagen, 1905), rewritten and enl. as Elemente der exakten Erblichkeitslehre (Jena, 1909; 3rd ed., 1926); Das AetherVerfahren beim Frühtreiben mit besonderer Berü cksichtigung der Fliedertreiberei (Jena, 1900); ü ber Erblichkeit in Populationen und in reinen Linien (Jena, 1903), first published in K. Danske Videnskabernes Selskabs Forhandlinger, no.3 (1903), abridged English trans. in James A. Peters, ed., Classic Papers in Genetics (Englewood Cliffs, N.J., 1959); Falske analogier, med henblik paa lighed, slaegtskab, arv, tradition og udvikling (Copenhagen, 1914); and Arvelighed i historisk og experimental belysning, 4th ed.(Copenhagen, 1923).

II. Secondary Literature. The following treat Johannsen’s life and work: Jean Anker, “Whihelm Johannsen,” in Danmark, 5 (1946- 1947), 295- 300, in Danish; P. Boysen Jensen, “Wilhelm Ludvig Johannsen,” in Kobenhavns Universitets Festskrift (Nov.1928), 105- 118, in Danish, with a bibliography of over 100 of Johannsen’s publications (1883- 1927); L. Kolderup Rosenvinge, “Wilhelm Ludvig Johannsen. I. Liv og personlighed,” in Oversigt over det K. Danske Videnskabernes Selskabs Forhandlinger (1927- 1928), 43- 68; and Ø jvind Winge, “Wilhelm Ludvig Johannsen. II. Videnskabeling Virksomhed,” ibid., 64- 69; and “Whihelm Johannsen,” in Journal of Heredity, 49 (1958), 82- 88.

Unpublished materials on Johannsen are in the archives of the Carlsberg laboratory, Copenhagen, and in the library of the American Philosophical Society, Philadelphia.

L. C. Dunn