In the wake of discoveries by Charles Darwin and Gregor Mendel, investigations into the genetic basis for heredity increasingly centered on the role of chromosomes. Wilhelm Roux argued that differentiation of cell types was linked to the distribution of chromosomes following cell division in the process termed “mitosis.” Although Roux would be proven wrong in suggesting chromosomes were distributed unequally, he was the first to demonstrate the sorting of chromosomes during division.
In 1859, the publication of Charles Darwin’s
On the Origin of Species led to what is arguably among the most important of modern scientific discoveries, an explanation of evolution as a result of natural selection
Improvements in microscopes combined with the implementation of staining techniques during the nineteenth century allowed for more precise observational studies of cell structures and organelles. Using newly developed aniline dyes, Walther Flemming observed the presence of threadlike structures from the nucleus of animal cells. Since these structures became visible during cell division, Flemming named the process mitosis, from the Greek word meaning “thread.” In 1888, Wilhelm Waldeyer named these structures chromosomes. Eduard Strasburger, carrying out similar observations using cells from plants, noted the presence of specific stages during cell division and, in 1884, named these phases prophase, metaphase, anaphase, and telophase, terms still used.
Wilhelm Roux was the only son of a university fencing master. Following service in the Franco-Prussian War (1870-1871), Roux entered a medical program at the University of Jena, completing his medical examinations in 1877. In 1879, he joined the institute at the University of Breslau, where he was to remain some ten years. Roux’s work was primarily in the emerging field of embryology, and his designation as the founder of experimental embryology is a tribute to his contributions. He was well aware of the importance of Darwin’s
Strasburger and Flemming had only recently described their work on mitosis. It was Roux’s belief that the complex processes described by his colleagues could be accounted for in the context of natural selection—that there was a function behind mitosis that enhanced the survival of the cell and the more complex organism. One application of this idea, albeit incorrect, was that stronger cells would crowd out weaker ones in the developing embryo.
In an 1883 essay, Roux described the physiological processes associated with chromosomes during cell division. Each chromosome (a modern term) divides longitudinally, with the separated material distributed to each daughter cell. It had appeared to Roux that during this process, chromosomes were randomly distributed throughout the nuclear region, and they perhaps were passed in like manner to the daughter cells. That is, Roux was unsure whether distribution of the chromosomes during cell division was equal, and he speculated that differentiation may in part be the result of an unequal distribution.
The pattern of movement of chromosomes to daughter cells also led Roux to speculate that their primary role in the cell was heredity. This idea was further applied by August Weismann in his theories on the role of chromosomes in development; Weismann argued that the maintenance of hereditary characteristics over generations was the result of chromosomes being passed from parent to offspring, an idea largely proved correct. However, Weismann incorrectly believed each chromosome was the equivalent of the others.
Roux’s incorrect assumption that differentiation is the result of alternative arrangements of chromosomes in cells is largely the reason why he remains a footnote in this area of biology. Much of his work during the later years at Breslau followed the same idea, that unequal chromosomal separation was necessary to explain the events during embryonic development. It remained for Theodor Boveri in the first years of the twentieth century to clarify the role played by chromosomes in development, as well as provide an explanation for their distribution.
After establishing that chromosomes were both necessary and sufficient to maintain genetic characteristics in fertilized sea urchin eggs, Boveri demonstrated that fertilization with two sperms resulted in the abnormal development of the organism. He concluded from these results that the inability of the sea urchin to develop normally was the result of unequal distribution of the chromosomes during cell division. If chromosomes were equivalent, as suggested earlier by Weismann, simply having extra chromosomes should not interfere with normal development. Boveri concluded that normal development required a precise number of chromosomes and that individual chromosomes probably carried specific characteristics. Boveri later refined this work in what would become his chromosomal theory of heredity.
Roux’s observation of processes associated with cell division—mitosis—led to one of the first reports explaining how chromosomal material is distributed to daughter cells. Only one year had passed, however, from the time Flemming had reported the presence of such structures in the nucleus of cells, and while some believed that chromosomes somehow played a role in heredity, the precise function of chromosomes needed confirmation.
Roux’s work was significant in providing further evidence for the function of chromosomes, a function that allowed for a mechanism by which chromosomal material may be passed to daughter cells. The mechanism duplicated or divided chromosomes along a longitudinal axis, which ensured their distribution to daughter cells following the completion of mitosis. In the context of natural selection, Roux’s ideas, largely theoretical, addressed the question of why such a complex mechanism might be beneficial for a cell.
One significant detail was absent from Roux’s hypothesis: He did not explain the process of differentiation. In his studies of embryology, Roux showed that cells underwent two separate divisions, in which the final set of daughter cells did not contain the same quantity of chromosomes as the original parent cell. This led to the mistaken hypothesis by Weismann that differentiation is, in part, the result of unequal distribution of chromosomes. Roux’s ideas required subsequent revision. Nevertheless, his work bridged the period between the discovery of chromosomes and the elucidation of their role in the heredity of both the cell and larger organisms.
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Baltzer, Fritz. “Theodor Boveri.” Science 144 (1964): 809-815. Biography of the scientist instrumental in developing a chromosomal theory of inheritance. Highlighted is his work in demonstrating the equal distribution of chromosomes during mitosis. -
Becker, Wayne, Lewis Kleinsmith, and Jeff Hardin. The World of the Cell. 6th ed. New York: Pearson/Benjamin Cummings, 2006. Comprehensive examination of the history of the study of the cell, with photographs of the process of cell division. -
Gillispie, Charles, ed. Dictionary of Scientific Biography. New York: Charles Scribner’s Sons, 1975. Professional biographies of the major figures and the roles they played in cell history. -
Harris, Henry. The Birth of the Cell. New Haven, Conn.: Yale University Press, 1999. History of cell theory and cell processes. -
Nurse, Paul. “The Great Ideas of Biology.” Clinical Medicine 3 (2001): 560-568. A brief but thorough and brilliant history of the development of cell biology and genetics by one of the top molecular cell biologists of modern times. -
Portugal, Franklin, and Jack Cohen. A Century of DNA. Cambridge, Mass.: MIT Press, 1977. Authors describe the experiments that led to determining DNA’s role in heredity. (DNA was discovered in 1869.) Roux’s observations are included in the early history. -
Sturtevant, A. H. A History of Genetics. Cold Spring Harbor, N.Y.: Cold Spring Harbor Press, 2001. An updated reprint of the subject of genetics, written by a key figure in the study of heredity. The author, a student of Thomas Hunt Morgan, the founder of modern genetics, played an important role in understandings of chromosomal theory. -
Thompson, D’Arcy Wentworth. On Growth and Form. Mineola, N.Y.: Dover, 1992. Thompson’s theory of transformation as an explanation of evolution was first described in 1917. Included is a history of cell theory, with reference to Roux’s work.
Schwann and Virchow Develop Cell Theory
Mendel Proposes Laws of Heredity
Metchnikoff Advances the Cellular Theory of Immunity
Behring Discovers the Diphtheria Antitoxin
Beijerinck Discovers Viruses
Rediscovery of Mendel’s Hereditary Theory
Karl Ernst von Baer; Charles Darwin; Francis Galton; Ernst Haeckel; Gregor Mendel; August Weismann.