We explore the field of biology from 1900-1950.
As outlined in the previous historical sketch, A Brief History Biology: Before 1900, around the turn of the 20th century, the science of biology faced two main challenges: (1) deepening its understanding of the material constitution of living things and the physical principles governing their activity; and (2) accounting for their origin, affiliations, and transformations over time.
With respect to the first challenge, a series of pathbreaking discoveries during the first half of the twentieth century established the basic picture of the fundamental material composition and functioning of living systems that we still adhere to today. For all practical purposes, this picture may be boiled down to two classes of facts:
To arrive at this detailed understanding of the material structure and functioning of cells, new experimental techniques were required, notably steady improvements in microscopy. Of equal importance, however, was the invention of special techniques of staining biological materials in order to give visual salience to specific structures of interest. Two of the most important individuals involved in this endeavor—Camillo Golgi (1843–1926) and Santiago Ramón y Cajal (1852–1934)—worked in the final decades of the nineteenth century, but were recognized by the joint awarding of one of the earliest Nobel Prizes in Physiology or Medicine, in 1906.
It was Hans Krebs (1900–1981) who used the new techniques perhaps to greatest advantage. Beginning in the 1930s, he demonstrated how the chemical reactions occurring in cells—considered collectively and taking waste products into account—constituted completed thermodynamic cycles (as in an ideal Carnot engine), thus closing the energetic books in accordance with the first law of thermodynamics. The most important of these “metabolic cycles” came to be called the “Krebs Cycle.”
Fritz Albert Lipmann (1899–1986) provided more detailed chemical analyses of the Krebs Cycle and other biochemical reaction networks, demonstrating the crucial role played by the nucleotide adenosine triphosphate (ATP) in all such reactions.
Gradually, it became clear that all fundamental activity of the cell is mediated by another class of macromolecules, namely, proteins. Here, Emil Fischer (1852–1919) played a very important conceptual role with his “lock-and-key” model of protein-substrate interaction. While at its core little more than a metaphor, Fischer’s fundamental lock-and-key model of protein function nevertheless successfully guided further research for decades and may be said to have withstood the test of time.
Fischer’s work was further refined by Linus Pauling (1901–1994), who conducted pioneering physical and biochemical studies of hemoglobin during the 1930s. These investigations should not be confused with the extremely important theoretical work Pauling had already contributed during the 1920s on the quantum mechanics of the chemical bond, or with the important conceptual and experimental work he would go on to do during the late 1940s and early 1950s on the structure of DNA.
With respect to the second main challenge mentioned above—the nature of the origins, affiliations, and transformations of the myriad forms of life on earth—during the latter part of the nineteenth century great hopes had been placed in Charles Darwin’s theory of natural selection as a means of explaining both how one living form (phenotype) is produced from another and how observable taxonomic patterns arise from such transformations. However, around the turn of the twentieth century, skepticism about the ability of the theory of natural selection to adequately explain the phenomena of natural history and paleontology became widespread among working biologists. This historical episode later came to be described as the “eclipse of Darwinism.”
This eclipse was primarily due to two factors: continuing conceptual problems regarding the status of the apparent teleological organization of living systems; and a complete lack of understanding of the physical principles underlying the phenomena of heredity. At this time, evolutionists began to entertain a variety of non-Darwinian theories, including neo-Lamarckism (inheritance of acquired characteristics), saltationism (large, single-step mutations), and orthogenesis (evolution by biological laws analogous to the laws of physics). Another result of this conceptual free-for-all was the recrudescence of “vitalism”—the idea that the living state of matter is physically sui generis, and that its distinctive character is attributable to a non-material animating principle analogous to the human mind or soul.
...around the turn of the twentieth century, skepticism about the ability of the theory of natural selection to adequately explain the phenomena of natural history and paleontology became widespread among working biologists.”
At the turn of the 20th century, detailed knowledge of the astoundingly complex molecular structure and functioning of cells outlined above still lay in the future. However, the phenomena associated with embryonic development in metazoans, which were far more experimentally accessible, were quite remarkable enough. This is why developmental biologists occupied the front ranks of the neo-vitalist movement.
The best known of these was Hans Driesch (1867–1941), who early in the new century gave a series of popular lectures based on his own experiments dating back to the 1890s. In them, he described how, following removal of one of the products of the first binary cell division in sea urchin blastomeres, the remaining half-blastomere was nevertheless able to return to a normal developmental path which typically resulted in a healthy (albeit smaller) adult form. Driesch believed this surprising compensatory power could only be explained by positing an unknown, immaterial force irreducible to any combination of mechanical interactions.
Other prominent developmental biologists of the day—including, notably, Ross G. Harrison (1870–1959), Hans Spemann (1869–1941), and Paul Weiss (1898–1989)—demonstrated equally remarkable feats of compensation by the developing organism after the destruction or transplantation of various cell clusters and adult tissues. This group introduced the concept of the “morphogenetic field” in an effort to provide a more-scientific, quasi-material account of the phenomena and so move beyond the classical vitalist position that the organizing life principle, being immaterial, lies beyond the scope of scientific investigation. This new vision of life—which may be viewed as a sort of halfway house between neo-vitalism and materialist reductionism—came to be known as “organicism.”
A number of physicists also took an interest in the question of the distinctive nature of life from an organicist perspective, including such luminaries as Niels Bohr (1882–1952), Erwin Schrödinger (1887–1961), and Pascual Jordan (1902–1980), who all published work in this area. Another group, which was centered around Cambridge University and which called itself the “Theoretical Biology Club,” included the X-ray crystallographer J.D. Bernal (1901–1971), in addition to the noted developmental biologists Joseph Needham (1900–1995) and C. H. Waddington (1905–1975).
A somewhat different approach to gaining insight into living systems consisted in modeling their structures and transformations abstractly, with the aid of mathematics. On Growth and Form, a pioneering book first published in 1917 by the Classicist, D'Arcy Wentworth Thompson (1860–1948), may be considered as the foundational work in the field now known as mathematical biology. A little later, Joseph Henry Woodger (1894–1981), a prominent member of the Cambridge Theoretical Biology Club, greatly expanded upon Thompson’s important work by attempting a formal axiomatization of biological processes.
...the philosophical materialism and reductionism which also formed an important part of the intellectual heritage handed down to 20th biologists by the 19th century slowly came to form the scientific consensus.”
Finally, the organicist impulse was given further concrete expression in a ground-breaking paper published in 1935 and known to historians as the “Three-Man Paper,” due to its co-authorship by the geneticist Nikolai Timoféeff-Ressovsky (1900–1981) and the physicists Max Delbrück (1906–1981) and Karl Zimmer (1911–1988). This paper, which reported on some of the effects of ionizing radiation on genetic mutation, may be considered as foundational for the discipline we now know as biophysics.
Neither the revival of vitalism nor the emergence of the new position known as organicism ever became a truly mainstream position, however. Rather, the philosophical materialism and reductionism which also formed an important part of the intellectual heritage handed down to 20th biologists by the 19th century slowly came to form the scientific consensus. Perhaps the most distinguished—and without a doubt the most widely read—critic of neo-vitalism was Jacques Loeb (1859–1924), who interpreted his own experiments on artificial parthenogenesis in stimulating embryological development in sea urchins as refuting Driesch, and who published his findings in his 1912 international bestseller, The Mechanistic Conception of Life.
During these same decades, the ground was also being quietly cleared for the revival of Darwinism. First came the rediscovery of the pioneering experiments of Gregor Mendel (1822–1884), who had determined the laws of genetic segregation and independent assortment in sexually reproducing metazoans. He had published his results in 1866 to very little notice. Mendel’s work was independently rediscovered and experimentally verified by three researchers who all published papers in 1900: the botanists Hugo de Vries (1848–1935) and Carl Correns (1864–1933) and the agronomist Erich von Tschermak (1871–1972).
This breakthrough did not take place in a vacuum, however. Rather, it was preceded by important work during the 1890s, notably, the germ-plasm/soma (in modern terms, genotype/phenotype) distinction first enunciated by the zoologist August Weismann (1834–1914) and the systematic studies of embryonic variability undertaken by the developmental biologist and evolutionary theorist, William Bateson (1861–1926).
Among other important factors that helped pave the way for the recovery of Mendel’s work, we must not overlook the experiments conducted, beginning in the 1890s, by the German developmental biologist Theodor Boveri (1862–1915), the American physician Walter Sutton (1877–1916), and, a little later, the American zoologist Edmund Beecher Wilson (1856–1939). Their experiments demonstrated the vital role played by chromosomes in embryonic development, and in cell division, more generally.
At this point, the history of genetics bifurcates into two broad experimental and theoretical streams: one investigating the abstract patterns of inheritance and of the transformation of species; the other addressing the underlying material basis of inheritance.
Taking the second stream first, the early work on inheritance sketched above was soon followed up by experiments conducted during the late 1920s and 1930s by George Beadle (1903–1989) and his colleagues at Caltech. The first to demonstrate, experimentally, the close connection between genes and proteins, Beadle gained fame through his “one gene, one protein” hypothesis, which—while now known to be vastly oversimplified—had an enormous impact on genetic research for many decades. A little later, Beadle did other very important work—along with Edward Tatum (1909–1975)—which demonstrated the control exercised by genes over the complex sequence of chemical reactions comprising central metabolism.
...the history of genetics bifurcates into two broad experimental and theoretical streams: one investigating the abstract patterns of inheritance and of the transformation of species; the other addressing the underlying material basis of inheritance.”
One of the most burning questions in biology now became the nature of the material constitution of the gene—which up to this point had been an essentially theoretical construct. In 1944, Oswald Avery (1877–1955) and his co-workers conclusively demonstrated that the genetic material is located within the DNA fraction of the chromosome and not in any sort of protein, as many investigators had previously believed.
In 1950, Erwin Chargaff (1905–2002) published the empirical relationship (now known as “Chargaff’s Rule”) he had observed to the effect that the combined amount of the nucleotide bases adenine and thymine in a given sample of DNA is always approximately equal to the combined amount of the bases cytosine and guanine.
With Avery’s proof and Chargaff’s Rule in hand, the race was on in earnest to solve the chemical structure of DNA—but that is a story for our next installment (see A Brief History of Biology: 1950–2000).
To return to the history of population genetics and its impact on evolutionary theory, it should be noted that hard on the heels of the rediscovery of Mendel’s Laws, systematic investigation of genetic inheritance was greatly intensified, notably, by Thomas Hunt Morgan (1866–1945), who chose the common fruit fly Drosophila melanogaster as his model organism. During the years just before and after 1910, Morgan and his students—working at Columbia University in what came to be called the “Fly Room”—churned out an enormous mass of statistical data on the patterns of inheritance in Drosophila under a wide variety of circumstances.
Several of Morgan’s students eventually set up their own Drosophila labs, notably Alfred Sturtevant (1891–1970) at Caltech and Hermann Joseph Muller (1880–1967) at the University of Texas at Austin. Inspired by the outstanding success of Morgan’s approach, biologists around the world began to work with Drosophila, finding in the tiny, short-lived fruit fly an optimal model organism for inheritance research. For example, before arriving at Caltech in 1927, Theodosius Dobzhansky (1900–1975) had worked with Drosophila in Saint Petersburg (Leningrad). Thus, it is Morgan more than anyone who may lay claim to the title of founder of the field of population biology.
Despite the firm empirical foundation now undergirding genetics, there was still lacking a sophisticated mathematical theory in the light of which the data might be usefully interpreted. This was provided by several generations of mathematicians and statisticians. The most important of these were Karl Pearson (1857–1936), who did his work during the years around the turn of the twentieth century, and the trio of J. B. S. Haldane (1892–1964), Ronald Fisher (1890–1962), and Sewall Wright (1889–1988), who all began their careers in the immediate aftermath of the First World War and continued for many years to make fundamental contributions to theoretical and applied statistics, population genetics, and evolutionary theory.
The aforesaid mathematicians were all Mendelians. They also accepted a broadly Darwinian theoretical framework. Indeed, their highly successful attempt to combine Mendelian genetics with Darwinism led directly to an astonishing revival of the theory of natural selection under the aegis of “neo-Darwinism.” The eclipse of Darwinism was now well and truly over.
However, the highly formal studies of the founders and developers of population biology still needed to be supplemented by more traditional field studies in natural history and paleontology in order to prove that the mathematicians’ equations matched the observable reality of changing biological forms over time. This piece of the puzzle was not long in coming.
In a series of ground-breaking monographs that appeared in swift succession over the next couple of decades, several distinguished biologists endeavored to create synthetic works laying out in exquisite detail various aspects of genetics, taxonomy, biogeography, and evolutionary theory as they had been developed up to that time, all under the neo-Darwinian banner.
First came Genetics and the Origin of Species by the geneticist Theodosius Dobzhansky (already mentioned above), published in 1937. This was followed by Systematics and the Origin of Species by the ornithologist Ernst Mayr (1904–2005) and Evolution: The Modern Synthesis by the developmental biologist Julian Huxley , both published in 1942. Next came Tempo and Mode in Evolution, published in 1944 by the paleontologist George G. Simpson (1902–1984). And, finally, in 1950, the botanist G. Ledyard Stebbins (1906–2000) published Variation and Evolution in Plants.
These works collectively gave birth to what would come to be known as the “Modern Evolutionary Synthesis,” which is a broad outline of the version of Darwinism that still reigns supreme (if no longer entirely unchallenged) to this day.
Find out which influencers have most contributed to advancing the field of biology over the last two decades with a look at The Most Influential People in Biology, for the years 2000 – 2020.
And to find out which schools are driving the biology field forward today, check out The Most Influential Schools in Biology for the years 2000-2020.
Or, continue exploring the fascinating history of the biology discipline with a look at a Brief History of Biology: 1950-2000.