Theodosius Dobzhansky (1900–1975)

Theodosius Dobzhansky studied genetics and evolutionary biology, primarily using fruit flies, in the Soviet Union and the United States during the twentieth century. Scholars credit his widely read 1937 book Genetics and the Origin of Species with providing one of the earliest and most impactful integrations of Charles Darwin’s theory of evolution by natural selection with Gregor Mendel’s theory of genetics and therefore contributing significantly to the Modern Synthesis. In his research, Dobzhansky studied wild populations of organisms such as fruit flies and found that populations of the same species can differ in the frequency of one or more genetic traits. Understanding the role of such genetic diversity in evolution became a central theme of his research. Later in his career, he wrote about the social implications of his research, including the relationship between biological and cultural notions of race. Through both his scientific papers and popular writings, Dobzhansky shaped the course of evolutionary biology in the twentieth century and influenced public discussions of race in the years following World War II.

1. Early Life and Education
2. Work in Kiev
3. Work in Petrograd
4. Early Work in America
5. Genetics and the Origin of Species
6. Later Research in America
7. Perspectives on Race
8. Legacy and Impact

Early Life and Education

Dobzhansky was born on 25 January 1900 in what was then Nemirov, the Russian Empire, and which is as of 2026 Nemyriv, Ukraine. He was the only child of Sophia Voinarsky, through whom Dobzhansky was a maternal cousin to novelist Fyodor Dostoevsky, and Grigory Dobrzhansky—the Russian surname containing the letter R when strictly transliterated—who taught mathematics in the Nemirov high school. According to a biography written by Dobzhansky’s daughter, Sophie Dobzhansky Coe, he was named in honor of Theodosius of Chernigov, a saint in the Russian Orthodox Church. Dobzhansky’s parents partook in a pilgrimage to the saint’s shrine and prayed for fertility after many years of being unable to conceive.

In an oral-history interview conducted by journalist Barbara Land in 1982, Dobzhansky asserted that he became a biologist in 1909 when he started collecting butterflies along with other boys in the neighborhood. But in 1910, an accident befell Dobzhansky’s father, who could not continue teaching, and the family moved from Nemirov to Kiev, Ukraine. Dobzhansky remained there through the turbulent years of 1910 to 1927, which included World War I, the Bolshevik Revolution, and several famines.

Dobzhansky attended middle and high school in Kiev, and by 1912 or 1913, he began investigating pond-water organisms under a microscope and dissecting frogs to examine their anatomy. As a high school student, Dobzhansky received a liberal-arts education consisting of Latin, natural history, physics, psychology, philosophy, mathematics, and literature. Despite his father’s ailing health and the family’s lack of a diverse private library due to financial struggle, Dobzhansky reports in his reminiscences that he was a prolific reader and a highly ranked student.

In the winter of 1915 to 1916, Dobzhansky met Victor Luchnik, a twenty-five-year-old college dropout who studied insects and specialized in beetles of the family Coccinellidae, commonly called ladybugs. Luchnik invited Dobzhansky to join the Entomological Society of Kiev and encouraged him to select a research concentration. Dobzhansky chose to study ladybugs as well, and, in 1917, he believed he discovered a new species in the Coccinellidae family, Coccinella lutshniki, in the debris along the banks of the Dnieper River in Kiev. In fact, the species had already been named Coccinella saucerottii in 1850 by Étienne Mulsant, a researcher in entomology, which is the study of insects. Nonetheless, in 1918, Dobzhansky published his first scientific paper where he described the physical characteristics of the species.

Work in Kiev

In May 1917, Dobzhansky graduated from high school and enrolled in the Saint Vladimir Imperial University of Kiev, renamed Taras Shevchenko National University of Kyiv as of 1939, to study biology with an emphasis on entomology. Prior to beginning classes, Dobzhansky began working with Sergei Kushakevich, a professor of zoology at the university whom he credits in the 1980 book The Evolutionary Synthesis with introducing him to the chromosome theory of inheritance. That theory suggests that chromosomes, which are structures within the nucleus of a cell, are the carriers of genes and are therefore the physical basis of heredity. For two or three years of his undergraduate degree, Dobzhansky used microscope slides to study snails with the goal of identifying the biological mechanisms of sexual differences. In the spring of 1918, Kushakevich recommended Dobzhansky for employment to Vladimir Vernadsky, a prominent researcher in the field of geochemistry, which is the study of the chemical composition of the earth’s rocks and minerals. Vernadsky tasked Dobzhansky with collecting living species for a project analyzing their role in geological processes, which, as Dobzhansky recounts in his interview with Land, was his first scientific employment. In 1919, at the age of nineteen, Dobzhansky also began teaching elementary biology courses at the university due to staffing shortages. During his undergraduate education, Dobzhansky’s father died on 10 January 1918, and his mother died on 9 May 1920.

Dobzhansky graduated with a degree in biology from the University of Kiev in 1921 and began full-time employment as an instructor in zoology at the Kyiv Polytechnic Institute, renamed the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” as of 2016, in Kiev. Although Dobzhansky was still primarily interested in entomology throughout his undergraduate degree and postgraduate employment, he states in his interview with Land that he began to use genetics as a means of understanding differences in insect speciation, which is the evolutionary process by which new species arise from a common ancestor. In approximately the winter of 1921 to 1922, Dobzhansky’s colleague Grigorii Levitsky traveled to Petrograd, renamed Saint Petersburg as of 1991, Russia, where he spent one or two weeks in the private library of Nicolai Vavilov, a researcher in genetics, reading about the most recent development in genetics produced by scientists in the United States and western Europe. Levitsky relayed what he had learned to Dobzhansky, essentially teaching his colleague and himself a course on genetics. To learn more about the rapidly progressing field of genetics, Dobzhansky began traveling to Moscow, Russia, to connect with academics at scientific institutes such as the Institute of Experimental Biology, a research organization founded in 1917 by Nikolai Koltzov, a professor of biology at Shanyavsky Moscow City People’s University in Moscow, Russia.

In Moscow, Dobzhansky obtained a collection of mutant strains of Drosophila melanogaster, a species of fruit fly, from Sergei Chetverikov, who was another researcher in genetics. Hermann Joseph Muller, a professor of genetics at the University of Texas at Austin, bred the mutant strains for single traits such as eye color, body color, or wing shape. Upon returning to Kiev, Dobzhansky used those fruit flies to study pleiotropy, a genetic phenomenon where a single gene influences multiple seemingly unrelated traits of an organism. Dobzhansky examined the genitalia of the fruit flies and determined that there were significant differences in the genital anatomy between mutants even though their various mutations had not been bred for that purpose, thus suggesting that those genes had pleiotropic effects. 

In 1924, Dobzhansky shared his experimental findings in his first publication on genetic inheritance in D. melanogaster, “Über den Bau des Geschlechtsapparats einiger Mutanten von Drosophila melanogaster” (On the Construction of the Genital Apparatus of Some Mutants of Drosophila melanogaster). Dobzhansky’s article was one of the first original studies in Drosophila genetics conducted in Russia. His publication caught the attention of Yuri Filipchenko, a researcher studying the relationship between genetics and evolution who was the new head of the Department of Genetics at the Petrograd State University, renamed Saint Petersburg State University as of 1992. Filipchenko offered Dobzhansky a research position to continue studying the pleiotropic effects of genes, and, in 1924, Dobzhansky left his position as a zoology instructor and moved to Petrograd. Shortly before relocating, Dobzhansky married Natalia Sivertzev, who also researched genetics and occasionally collaborated with Dobzhansky throughout their almost forty-five years of marriage.

Work in Petrograd

Although Filipchenko primarily studied wheat genetics during Dobzhansky’s employment at his laboratory, Dobzhansky continued to study genetic transmission in insects, focusing particularly on the relationship between the principles of heredity established by Gregor Mendel, an early researcher in genetics, in the 1860s and the theory of evolution by natural selection proposed by Darwin in 1859. In 1924, Dobzhansky published an article titled “Nasledstvennost' i mutatsiia” (Inheritance and mutation) in the journal Chelovek i Priroda (Man and Nature), popularizing the work of Thomas Hunt Morgan, a researcher at Columbia University in New York City, New York, who also studied the genetic characteristics of fruit flies. In that paper, however, Dobzhansky independently asserted that the role of mutations in evolution is to provide the material upon which natural selection acts. Dobzhansky explained that, given how some mutations result in advantageous physical characteristics, those beneficial mutations persist in populations because the organisms that possess them tend to survive and reproduce. He further elaborated on those ideas in a review essay for the journal Priroda (Nature) titled “Mutatsii i vidoobrazovanie” (Mutations and speciation), published in 1926. There, Dobzhansky referenced prior work on Drosophila to claim that speciation is due to an accumulation of mutations.

For nearly four years, from 1924 to 1927, Dobzhansky studied pleiotropy in Drosophila in Filipchenko’s laboratory, producing work that eventually caught the attention of Morgan. Filipchenko and Morgan already had a working relationship, and, after correspondence among all three scientists, Dobzhansky obtained permission to work as a researcher within Morgan’s laboratory for a year. In 1927, he received funding from the International Education Board, an organization established by the Rockefeller Foundation in 1923 to support the advancement of education worldwide and, in practice, focusing on natural science and agriculture. On 27 December 1927, Dobzhansky arrived in the United States to work with Morgan at Columbia University. Although the fellowship position was a temporary arrangement, Dobzhansky and his wife found the means to live permanently in the United States. Dobzhansky believed that he and his wife technically broke a Soviet law by failing to return to their country upon completion of the fellowship and were therefore in danger of capital punishment if they returned to Soviet soil. Their only daughter, Sophie, was born in 1933 in Pasadena, California, and grew up to be a food historian known principally for her study of the history of chocolate.

Early Work in America

When Dobzhansky joined Morgan at Columbia University, Morgan was focused on researching the chromosome theory of inheritance. Walter Sutton, a researcher in genetics, and Theodor Boveri, a researcher in cell biology, developed the theory in 1902 and 1903 using observations of cell division. According to Keith Benson, a professor of the history of science at the University of Washington in Seattle, Washington, Morgan was initially skeptical of the idea, but he started experimenting with D. melanogaster in his laboratory, dubbed the Fly Room, to study patterns of heredity. By observing that a mutation for white eyes was only found amongst male flies, Morgan asserted that the inheritance pattern could only be explained if the mutant gene responsible for that physical characteristic was linked to a sex chromosome. Dobzhansky joined Morgan’s research on the genetics of fruit flies and focused on a project studying the genetics of sex. The laboratory group worked in New York City during most of the year and relocated to the Marine Biological Laboratory in Woods Hole, Massachusetts, during the summers. There, in 1928, and following Muller’s finding the previous year that x-rays could cause mutations, Dobzhansky explored how x-rays altered fruit-fly chromosomes.

In the summer of 1928, Morgan left Columbia University to found a new program in biology at the California Institute of Technology, or Caltech, in Pasadena, California. Several of his collaborators joined him, including Dobzhansky, who moved to Pasadena in 1929 and became assistant professor of genetics, and, in 1936, became a professor of genetics, all at Caltech. He continued working in fruit-fly cytogenetics, a branch of genetics that studies the structure and function of chromosomes within cells. His 1929 publication, “The Influence of the Quantity and Quality of Chromosomal Material on the Size of the Cells in Drosophila melanogaster,” examined the effects of chromosomal mutations on cell size.

In 1935, coupled with his earlier studies on the genetics of sex, Dobzhansky formulated the biological species concept, which is the biological definition of species as organisms that are physiologically incapable of interbreeding, a concept that remains fundamental in evolutionary genetics. In 1936, Dobzhansky and Alfred Henry Sturtevant, another researcher in Morgan’s laboratory, began using Drosophila pseudoobscura to understand evolution in natural populations. The pair published their research in a paper titled, “Inversions in the Third Chromosome of Wild Races of D. pseudoobscura, and Their Use in the Study of the History of the Species,” where they reported on their studies of overlapping inversions, which are pieces of the same chromosome that are flipped with respect to the regular orientation. Using those inversions helped them to infer evolutionary relationships among species by showing the way sequences of genes change across different species.

Genetics and the Origin of Species

In April 1936, Leslie Clarence Dunn, a professor of zoology at Columbia University, invited Dobzhansky to deliver a series of lectures at the university, suggesting that the lectures could serve as the precursor to writing a general treatise on evolutionary genetics. According to Joe Cain, a researcher studying the history of evolutionary biology, Dobzhansky responded favorably to that idea and wrote back in May with the proposition of creating a work titled Genetics and the Origin of Species, asserting that the aim of the book was to add genetics to Darwin’s theory of evolution. He outlined the book into two parts: the first containing data on sources of evolutionary change and the second containing analysis of how those genetic mechanisms culminate in the formation of species. After delivering the lectures at Columbia University in October and November 1936, Dobzhansky returned to Pasadena, and Columbia University Press accepted his book proposal in December 1936. By April 1937, Dobzhansky had completed an initial manuscript, which he sent to Dunn for editing, and, in October 1937, Columbia University Press published the first edition of Genetics and the Origin of Species.

That first edition used Dobzhansky’s previous research, as well as the work of other evolutionary theorists who had developed mathematically based stances of natural selection as a genetic process, known as population genetics, to address the genetic mechanisms of speciation. Dobzhansky asserted that mutations occur frequently and randomly, and they provide the raw genetic material for natural selection to act upon. Thus, Dobzhansky portrayed the process of evolutionary population genetics as occurring on three levels: the origin of raw genetic material through mutations, larger changes in populations through variations in the frequencies and combinations of mutations, and the process of those mutations becoming fixed, or permanent, within populations due to reproductive isolation, or conditions that prevent different populations from interbreeding. Researchers in the field of evolutionary biology identify Genetics and the Origin of Species as one of the first instances of the modern synthesis of evolutionary theory, combining Darwinian selection theory with a population-oriented view of Mendelian genetics as a means of explaining the origin of biological diversity.

Dobzhansky published extensively revised versions of the book in 1941 and 1951, removing chapters and deemphasizing rapid modification and randomness in evolutionary change. The second edition focused more heavily on the role of genetic and chromosomal mutations in Dobzhansky’s synthetic theory of evolution, and the third edition discussed the genetic foundations of adaptive polymorphisms, which is when two or more distinct forms of a trait persist within a population because each form provides an advantage in a particular environment or under specific conditions. Dobzhansky considered his 1970 book Genetics of the Evolutionary Process to be an unofficial fourth edition, but the content had changed too much to appear under the same title.

Later Research in America

In 1940, Dobzhansky returned to Columbia University to work as a professor of zoology, a position that he maintained until 1962. He continued studying genetics in fruit flies and was amongst the first to conduct experiments showing that natural selection can influence the frequency of inversion polymorphisms. In 1947, Dobzhansky published a study that simulated how genetic drift, which is a type of random gene fluctuation, can interact with natural selection in fruit-fly populations. He observed multiple caged populations of D. pseudoobscura with known population-specific chromosomal variants over the course of several months, noting that flies heterozygous for a chromosomal variant, meaning they possessed two different versions of the variant, became more prevalent in the population and exhibited better survival rates than flies that were homozygous, meaning they possessed two of the same copies of the variant. Together, by the early 1950s, those studies influenced Dobzhansky’s formulation of the balance hypothesis of population structure, a view which asserts that balancing selection plays an important role in maintaining genetic variation within populations, therefore supporting those populations’ adaptabilities in the face of environmental changes. Balancing selection occurs, for example, when heterozygous members of a population are better able to survive and reproduce than homozygous ones. In contrast to the balance hypothesis, proponents of the classical hypothesis of population structure, the most prominent advocate of which was Muller, held that selection acted primarily to purge genetic diversity from populations, ensuring that only the versions of genes best suited to support the survival of the population persist. In Muller’s view, selection favors the creation of homozygous individuals. Dobzhansky’s and Muller’s opposing stances on the role of genetic diversity in natural selection became known among scholars as the classical/balance controversy.

Perspectives on Race

In addition to studying specific organisms and species in their evolutionary context, Dobzhansky contributed to discussions of what race means in biological organisms, including humans. According to Michael Yudell, dean and a professor at the College of Health Solutions at Arizona State University in Phoenix, Arizona, prior to Dobzhansky’s research, scientists defined race in typological terms, which is the view that humans can be divided into discrete, homogeneous units called races based on shared physical traits such as skin color, hair texture, and skull shape. That concept of race, Yudell asserts, perpetuated discriminatory actions and stereotypes because it implied significant biological differences between races. Dobzhansky reconceived races as populations that differ in the allele frequencies of one or more genes, indicating that race was a fluid concept that, although biologically based, can change depending on what genes are being investigated. Therefore, according to Dobzhansky’s definition, there could be only a few or many races based on which gene-frequency differences scientists choose as criteria. Moreover, there is more genetic variation within racial groups than there is between them. For Dobzhansky, those findings demonstrated why racism was wrong and unscientific: everyone is a unique individual and not a reflection of a racial type. Writing during the Civil Rights era in the US, a period of organized activism during the 1950s and 1960s to end racial segregation and secure equal rights for African Americans, Dobzhansky was an outspoken critic of scientists who asserted that certain races were biologically superior, such as Carleton Coon, a researcher in anthropology at the University of Pennsylvania in Philadelphia, Pennsylvania. The racial hierarchies put forth by Coon and others historically served as scientific justification for segregation. While Dobzhansky criticized older views of race and condemned what he saw as instances of scientific racism, Yudell writes that Dobzhansky nevertheless remained convinced that race was a useful concept in biology because it served as a methodological tool to study human populations.  

In his assertion that race was a biologically meaningful concept and one that society should recognize, Dobzhansky clashed with other individuals in the scientific community such as anthropology researchers Ashley Montagu and Frank Livingstone. Montagu argued that the term race possessed so many negative associations that it was in society’s best interest to eliminate the term altogether. Dobzhansky disagreed and asserted that scientific findings on race should not be influenced by social misuses of the term. In 1950, Dobzhansky was among the scientists who publicly criticized the “Statement on Race” put forward by the United Nations Educational, Scientific and Cultural Organization, or UNESCO, which was written mostly by social scientists under the direction of Montagu. In the “Statement on Race,” the authors consider race to be what they call a social myth rather than a biological reality, as there are no significant biological differences between races. Dobzhansky and several other biologists argued that the statement exaggerated the degree of similarity among human races and overstated what was known about race. Dobzhansky helped to revise the statement, and, in 1951, he was one of the authors of the UNESCO “Statement on the Nature of Race and Race Differences.” There, the authors acknowledged genetic variation between human populations, but they emphasized that those differences were small and did not justify racial hierarchies or the concept of certain races being less intellectually or emotionally developed.

In the June 1962 issue of Current Anthropology, in an article titled, “On the Non-Existence of Human Races,” Livingstone and Dobzhansky debate the merits of using the term race to describe the patterning of human genetic variation. Livingstone famously argued that there are no human races, only clines, which are continuous geographic gradients in a specific biological or genetic trait across a population. For example, traits like skin color or hair texture can change progressively over geography in response to environmental factors like climate. Therefore, dividing humans into discrete racial categories based on biological traits does not accurately capture that gradient, and scientists should not use the concept of race when studying humans. In response, Dobzhansky once again defended the notion that human races exist as clusters of genetically similar individuals, although they might not correspond to what non-scientists mean when they use that term.  

From the 1940s through the 1970s, Dobzhansky wrote or co-authored several books on race for a popular audience. In 1946, he co-authored Heredity, Race and Society with Dunn, which sought to explain why the modern science of genetics does not support race prejudice or racism. Dunn and Dobzhansky argue that every human is genetically unique, therefore rendering racism illogical and wrong from a scientific perspective. In his 1964 book, Heredity and the Nature of Man, Dobzhansky rejects the concept of racial superiority and asserts that culture, not race, is the most important determinant of the nature of a society. Despite Dobzhansky’s work in refuting the arguments used to justify racist and eugenic ideologies and policies, he nevertheless joined the Board of Directors of the American Eugenics Society, or AES, in 1964. The AES was an organization dedicated to the aim of improving the genetic makeup of the human species through controlled reproduction of different races and classes of people. Dobzhansky held that individuals with serious diseases should not reproduce.

Legacy and Impact

Throughout his scientific career, Dobzhansky produced nearly 600 scientific publications, including a dozen books. Many scholars consider Genetics and the Origin of Species to be one of the most influential books of evolutionary theory in the twentieth century. His integration of Mendelian genetics with Darwinian principles contributed to the establishment of the modern evolutionary synthesis. Through his writings on race, he shaped popular discussion of that topic in the post-World War II years. Dobzhansky also mentored many graduate students, some of whom went on to have notable careers as researchers of genetics and evolutionary biology, including Richard Lewontin, Francisco Ayala, and Bruce Wallace. 

Dobzhansky received multiple awards from the National Academy of Sciences, including the Daniel Giraud Elliot Medal in 1946 and the Kimber Genetics Award in 1958, as well as the National Medal of Science in 1964. He received honorary degrees from over twenty universities across several continents and served as president for a variety of scientific societies, including the Genetics Society of America, the American Society of Naturalists, and the Behavior Genetics Association.

On 22 February 1969, Dobzhansky’s wife Natalia died of coronary thrombosis, or a blood clot in one of the heart’s arteries. Although he had previously retired from teaching, Dobzhansky accepted a position as an adjunct professor of genetics at the University of California, Davis in 1971. In 1973, Dobzhansky, who came from a long line of Eastern Orthodox priests on his maternal side and remained religious all his life, published his essay titled, “Nothing in Biology Makes Sense Except in the Light of Evolution.” In it, he criticizes anti-evolution perspectives in creationism, or the belief that the universe and all life on Earth originated from the act of a deity, and promotes theistic evolution, or the belief that the creation of the universe by a deity is compatible with evolution. 

Dobzhansky died from heart failure on 18 December 1975, in Davis, California, at the age of seventy-five.

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