Wilhelm Ludvig Johannsen helped lay the foundation for the modern science of genetics. His studies with bean plants enabled him to distinguish between genotype (characteristics that can undergo natural selection) and phenotype (characteristics independent of natural selection.) He established a new vocabulary for studying heredity, including the word "gene," and was among the first biologists to apply rigorous statistical methods to research data. Although Johannsen was trained as a pharmacist, had no formal university degree, and pursued his research mostly as an accomplished amateur, he was eventually made a professor at the University of Copenhagen and was widely revered for his scientific contributions. Ojvind Winge reported in Journal of Heredity that Johannsen once wrote about his unusual intellectual background: "That training which... [formally educated] naturalists received has, partly due to its almost purely descriptive direction, provided them with blinkers which I, with all my scientific unsophistication, thank Heaven for that I lack, even though my glance is thereby more scattered, more shifting, and often too little concentrated in one direction--I am, and always will be, a free-lance in science." Although some of Johanssen's ideas have been superseded, the core of his work occupies the crossroads between old and new ways of thinking in the sciences of heredity and evolution.
Johannsen was born to Otto and Anna Ebbesen Johannsen in Copenhagen, Denmark. His father, an army officer, was transferred to the city of Helsingoer when Johannsen was eleven years old. Johannsen later attributed his scientific interest to a combination of his mother's appreciation for the natural world, and his father's sense of order and discipline. Despite an excellent early education in Copenhagen, and a good performance on university entrance examinations some years later, Johannsen was financially unable to attend college full time. Instead, he was apprenticed to a pharmacist in 1872, and worked in that field both in Denmark and Germany (he spoke and wrote fluent German) for several years. During that time, he taught himself botany and chemistry, read widely in many fields, and continued a more formal education in pharmacy that culminated in high honors on a German pharmaceutical examination.
In 1881, Johannsen started work in the new Carlsberg Laboratory (financed by profits from the Carlsberg Breweries) as an assistant to the famous chemist Johann Kjeldahl. There he began doing actual research, particularly on plant metabolism. After 1887, he supported his own research with stipends and a small inheritance. In 1892, he left the Carlsberg Laboratory to take a post as lecturer, and finally, in 1903, he became professor of botany and plant physiology, at the Copenhagen Agricultural College. The University of Copenhagen hired him in 1905 as a professor of plant physiology (not without controversy, given Johannsen's lack of formal education in the field), and in 1917, he became rector of that university. Johannsen traveled frequently throughout his career, and became well known as a witty and interesting speaker.
Initially, Johannsen's research dealt with the anatomy and physiology of barley and wheat. He developed a new method for stimulating dormant plants in winter, and developed a large-grained barley that was also low enough in nitrogen to be useful in the beer making process. Johannsen gradually began studying inherited characteristics in bean plants, particularly the Princess bean. Normally, any single species shows some variation in each of its characteristics; individual organisms in the species will have one of the variations of each character. Natural selection operates because individual organisms possessing the most useful set of variations will be the most likely to survive and reproduce. The other variations continue to survive (although in fewer individuals) as long as they are not actively detrimental to the species. Beans are self-fertilized, so Johannsen was able to show, by careful breeding, that within each species there existed "pure lines" of individuals who possessed a single set of inheritable variations. Generation after generation, the inheritable characteristics of a pure line remained the same. Variation of characteristics in a whole species therefore results from all the pure lines mixing together. Johannsen showed that any observable difference in the individuals of a single pure line--different seed size, for example--was not inheritable and was entirely the result of environmental forces such as amount of light or water.
This work was important because the study of inheritance was in its infancy at the time, and very few genetic principles were even partially understood. Darwin's work on evolution as a result of natural selection was taken seriously, but some scientists suspected that some observable variations in characteristics were the result of heredity and some were the result of environment. They had only limited ability to differentiate the two, and were not at all certain whether environmental characteristics could be inherited or not. Johannsen brought the beginnings of order to this muddle by clearly showing with statistical analysis of his pure lines that internal variations were inherited and environmental variations were not; thus, a difference existed between genotype (the internal blueprint of the organism) and phenotype (how the organism looks, metabolizes, and behaves in its unique surroundings.)
Following the turn of the century, Johannsen recognized the importance of Austrian botanist Gregor Mendel's work with garden peas, which revealed characteristics of inheritance. As a result Johannsen began meshing Mendelian principles with his own ideas. He had more difficulty with the idea that genes were actual locations on the chromosome--he preferred a more mathematical and abstract view of them--and it was many years before he accepted the theory. After his work was finished on the pure lines, he gave up experimentation and spent the rest of his career writing and critically analyzing the sciences.
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