Wilhelm Johannsen (1857 - 1943)

    Wilhelm Johannsen (1857–1927) was a Danish botanist and geneticist whose experiments with the common bean, Phaseolus vulgaris, helped clarify the relationship between heredity and environmental variation. He worked as Professor of Plant Physiology at the University of Copenhagen. His experiments published in 1903 showed them from a single bean population of mixed origin, artificial selection could establish pure lines with lower and higher mean weights outside the range of the parental population. He also demonstrated that these lines remained variable within themselves, and was among the first to show that variation in populations was influenced both by genes and the environment.

    Johannsen's experiments demonstrated the existence of hidden hereditary variation within populations, and also indicated that there were limits to artificial selection on that variation.  His 1909 Elemente der exakten Erblichkeitslehre [Elements of the Exact Theory of Heredity] introduced (in German) the terms gene, genotype, and phenotype in the description of his experiments, and became a standard textbook in English translation.