DOBZHANSKY, THEODOSIUS

(b. Nemirov, Ukraine, Russia, 25 January 1900; d. Davis, California, 18 December 1975)

genetics, evolution.

Dobzhansky was the only child of Sophia Voinarsky and of Grigory Dobrzhansky (the precise transliteration of the Russian family name), a teacher of high school mathematics. In 1910 the family moved to the outskirts of Kiev. During his early gymnasium years, Dobzhansky became an avid butterfly collector. In the winter of 1915–1916, he met Victor Luchnik, a twenty-five-year-old college dropout who was a dedicated entomologist specializing in Coccinellidae beetles. Luchnik convinced Dobzhansky that butterfly collecting would not lead anywhere, that he should become a specialist. Dobzhansky chose to work with ladybugs, which were the subject of his first scientific publication (1918).

Before Dobzhansky graduated in biology from the University of Kiev in 1921, he was hired as an instructor in zoology at the Polytechnic Institute in Kiev. He taught there until 1924, when he became an assistant to Yuri Filipchenko, head of the new department of genetics at the University of Leningrad. Filipchenko had started research with Drosophila fruitflies, and Dobzhansky was encouraged to investigate the pleiotropic effects (that is, affecting different features of an organism) of genes.

In 1927, Dobzhansky obtained a fellowship from the International Education Board of the Rockefeller Foundation and arrived in New York on December 27 to work with Thomas Hunt Morgan at Columbia University. In 1928 he followed Morgan to the California Institute of Technology, where he was appointed assistant professor of genetics in 1929 and professor of genetics in 1936. Dobzhansky returned to New York in 1940 as professor of zoology at Columbia University, where he remained until 1962, when he became professor at the Rockefeller Institute (now Rockefeller University), also in New York City. In 1970 Dobzhansky became emeritus at Rockefeller University; in September 1971, he moved to the department of genetics at the University of California, Davis, where he was adjunct professor until his death.

On 8 August 1924 Dobzhansky married Natalia (Natasha) Petrovna Sivertzev, a geneticist in her own right, who at the time was working with the biologist Ivan Schmalhausen in Kiev; they had one daughter, Natasha died in 1969.

During a routine medical checkup in 1968, it was discovered that Dobzhansky suffered from chronic lymphatic leukemia, one of the least malignant forms of leukemia. He was given a prognosis of “a few months to a few years” to live. Over the following seven years, the progress of the leukemia was unexpectedly slow and—even more surprising to his physicians—it had little, if any, noticeable effect on his energy and work habits. However, the disease took a conspicuous turn for the worse in the summer of 1975. In mid-November, Dobzhansky started to receive chemotherapy, but continued living at home and working at the laboratory. He was convinced that the end of his life was near and feared that he might become unable to work and to care for himself. This never came to pass. He died of heart failure on 18 December 1975, as he was being rushed to the hospital. The previous day he had, as usual, worked in the laboratory.

Dobzhansky was a religious man, although he apparently rejected fundamental beliefs of traditional religion, such as the existence of a personal God and of life beyond physical death. His religiosity was grounded on the conviction that there is meaning in the universe. He saw that meaning in the fact that evolution has produced the stupendous diversity of the living world and has progressed from primitive forms of life to mankind. Dobzhansky held that, in mankind, biological evolution has transcended itself into the realm of self-awareness and culture. He believed that somehow mankind would eventually evolve to higher levels of harmony and creativity.

Dobzhansky was one of the most influential biologists of the twentieth century; he also was one of the most prolific. The complete list of his publications has nearly six hundred titles, including a dozen books. The gamut of subject matter is enormous: results of experimental research in various biological disciplines, works of synthesis and theory, essays on humanism and philosophy, and others. These diversified works are nevertheless unified— biological evolution is the theme that threads them together. The place of biological evolution in human thought was best expressed, according to Dobzhansky, in a sentence that he sometimes quoted from the Jesuit paleontologist Pierre Teilhard de Chardin: “Evolution is a light which illuminates all facts, a trajectory which all lines of thought must follow—this is what evolution is.”

Dobzhansky’s prodigious scientific productivity was made possible by incredible energy and very disciplined work habits. His success as the creator of new ideas and as a synthesizer was, at least in part, based on his broad knowledge, his excellent memory, and an incisive mind able to see the relevance that a new discovery or a new theory might have for other theories or problems. His success as an experimentalist depended on a wise blending of field and laboratory research; whenever possible, he combined both in the study of a problem, using laboratory studies to ascertain or to confirm the causal processes involved in the phenomena discovered in nature. He obtained the collaboration of mathematicians to design theoretical models for experimental testing and to analyze his empirical observations statistically. He was no inventor or gadgeteer, but he had an uncanny ability to exploit the possibilities of any suitable experimental apparatus or method.

Dobzhansky was a world traveler and an accomplished linguist, fluent in six languages and able to read several more. He was a good naturalist and never lacked time for a hike, whether in the California Sierras, the New England forests, or the Amazonian jungles. He loved horseback riding but engaged in no other sports. His interests covered the plastic arts, music, history, Russian literature, cultural anthropology, philosophy, religion, and, of course, science.

Dobzhansky recognized and generously praised the achievements of other scientists; he admired the intellect of his colleagues, even when admiration was alloyed with disagreement. He made many lasting friendships, usually started by professional interactions. Many of Dobzhansky’s friends were scientists younger than himself who either had worked in his laboratory as students, postdoctoral fellows, or visitors, or had met him on one of his trips. He was affectionate and loyal toward his friends; he expected affection and loyalty in return. Dobzhansky’s exuberant personality was manifest not only in his friendships but also in his antipathies, which he was neither able nor, often, willing to hide.

Dobzhansky was an excellent classroom teacher. More than thirty graduate students obtained the Ph.D. under him, and he had an even greater number of postdoctoral and visiting associates, many of them from foreign countries. Dobzhansky spent long periods of time in foreign academic institutions, and was largely responsible for the establishment or development of genetics and evolutionary biology in Brazil, Chile, and Egypt.

Dobzhansky gave generously of his time to other scientists, particularly to young ones, and to students. On the other hand, he resented time spent on committee activities, which he shunned as much as he reasonably could. Throughout his academic career, Dobzhansky avoided administrative posts; he alleged, perhaps correctly, that he had neither the temperament nor the ability for management. Most certainly, he preferred to dedicate his working time to research and writing rather than to administration.

Dobzhansky received numerous honors and awards. He was elected to the U.S. National Academy of Sciences, to the American Academy of Arts and Sciences, the American Philosophical Society, and many foreign academies, including the Royal Society of London, the Royal Swedish Academy of Sciences, the Royal Danish Academy of Sciences, the Brazilian Academy of Sciences, the Academia Leopoldina, and the Accademia Nazionale dei Lincei. He was president of the Genetics Society of America (1941), the American Society of Naturalists (1950), the Society for the Study of Evolution (1951), the American Society of Zoologists (1963), the American Teilhard de Chardin Association (1969), and the Behavior Genetics Association (1973).

Dobzhansky received the Daniel Giraud Elliot Medal (1946) and the Kimber Genetics Award (1958) from the National Academy of Sciences, the Darwin Medal from the Academia Leopoldina (1959), the Anisfield-Wolf Award (1963), the Pierre Lecomte du Nouy Award (1963), the Addison Emery Verrill Medal from Yale University (1966), the Gold Medal Award for Distinguished Achievement in Science from the American Museum of Natural History (1969), and the Benjamin Franklin Medal from the Franklin Institute (1973). In 1964 he received the National Medal of Science.

The Modern Synthesis of Evolutionary Theory . Dobzhansky’s most significant contribution to science was his role in formulating the modern synthesis of evolutionary theory. His Genetics and the Origin of Species (1937) is considered by some to be the most important book on evolutionary theory in the twentieth century. The title of the book suggests its theme: the role of genetics in explaining the origin of species, a synthesis of genetic knowledge and Darwin’s theory of evolution by natural selection. Considerably revised editions of this book were published in 1941 and 1951. Genetics of the Evolutionary Process, published in 1970, was considered by Dobzhansky as the fourth edition of the earlier book, except that the content had changed too much to appear under the same title.

By the early 1930’s the work of R. A. Fisher and J. B. S. Haldane in Great Britain, and of Sewall Wright in the United States, had provided a theoretical framework for explaining the process of evolution, particularly natural selection, in genetic terms. This work had a limited impact on the biology of the time because it was formulated for the most part in mathematical language, and it was almost exclusively theoretical with little empincal support. In Genetics and the Origin of Species, Dobzhansky completed the integration of Darwinism and Mendelism initiated by the mathematicians in two ways. First, he gathered the empirical evidence that corroborated the mathematico-theoretical framework. Second, he extended the integration of genetics with Darwinism far beyond the range of issues treated by the mathematicians, and into critical evolutionary issues—such as the process of speciation—not easily subjected to mathematical treatment. Moreover, Dobzhansky’s book was written in prose understandable to biologists.

The line of thought of Genetics and the Origin of Species is surprisingly modern—in part, no doubt, because the book established the pattern that successive evolutionary treatises would largely follow. The book starts with a consideration of organic diversity and discontinuity. Then, successively, it deals with mutation as the origin of hereditary variation, the role of chromosomal rearrangements, variation in natural populations, natural selection, the origin of species by polyploidy, the origin of species through gradual development of reproductive isolation, physiological and genetic differences between species, and the concept of species as natural units.

Genetics and the Origin of Species was received with great excitement by the biological community, and it inspired other biologists to bring into the modern synthesis of evolutionary theory the contributions of such fields as systematics (Ernst Mayr, 1942), zoology (Julian Huxley, 1942), paleontology (George G. Simpson, 1944), and botany (G. Ledyard Stehbins, 1950). Genetics and the Origin of Species also provided a conceptual framework that stimulated experimental research for many years.

Experimental Population Genetics . Dobzhansky was not only a theorist of evolution but also an experimentalist. During half a century of intensive research and publication, he made fundamental empirical contributions to virtually every major area of population and evolutionary genetics.

Dobzhansky’s first contribution to population genetics appeared in 1924—an investigation of local and geographic variation in the color and spot pattern of two Coccinellidae genera, Harmonia and Adalia. These ladybugs exhibit local polymorphisms, which in some species vary from one locality to another, Dobzhansky explained the genetic variation within and between populations as results of the same fundamental evolutionary processes. Some cardinal themes of his evolutionary theory are already present in this work: the pervasiveness of genetic variation, geographic variation as an extension of local polymorphism and as the first but reversible step toward species differentiation. He continued the study of natural populations of ladybugs until he left Russia in 1927, and on occasion returned to them (for instance, a paper in 1933 and a monograph in 1941).

The beginning of Dobzhansky’s studies on the population genetics of Drosophila can be traced to 1933, when he published a paper on the sterility of hybrids between D. pseudoobscura and D. persimilis (then known as D. Pseudoobscura races A and B). In a series of papers, he investigated the physiological, developmental and genetic causes of hybrid sterility. This work developed from the convergence of two independent lines of investigation: the genetics of chromosomal translocations and the study of sex determination. It led in 1935 to a formulation of the concept of (sexually reproducing) species still accepted today: “that stage of the evolutionary process at which the once actually or potentially interbreeding array of forms becomes segregated in two or more separate arrays that are physiologically incapable of interbreeding.”

This notion establishes that reproductive isolation is what sets species apart. It is also an evolutionary definition that sees speciation as a dynamic process of gradual change. Dobzhansky introduced in 1935, and formally proposed in 1937, the term “isolating mechanisms” to designate the phenomena that impede gene exchange between species. Throughout his life he identified, classified, and investigated the various kinds of isolating mechanisms.

The experimental contributions of Dobzhansky to population genetics are so numerous and so diversified as to defy the possibility of a brief summary. Following is a discussion of a few major areas of research, with the years when he published some of the major papers in each subject.

Dobzhansky’s classical studies on the geographical and temporal variation of chromosomal arrangements in Drosophila pseudoobscura and its relatives started with a publication in 1936; in 1938 he published a paper on altitudinal variation; in 1943, a paper on seasonal variation, followed in 1946 by a laboratory study (in collaboration with Sewall Wright) showing adaptive differences (with respect to temperature) between chromosomal arrangements. Numerous other publications on this subject appeared through the 1930’s and 1940’s, and continued throughout Dobzhansky’s life. Starling in the 1950’s the study of geographical variation in chromosomal arrangements was extended to the D. willistoni group of tropical species, which exhibit even greater degrees of local polymorphism and geographical variation than D. pseudoobscura.

While working with Alfred H. Sturtevant. Dobzhansky realized that the evolutionary phylogeny of chromosomal arrangements can be reconstructed by deciphering the patterns of overlapping chromosomal inversions found in natural populations of Drosophila; the first phylogeny was published in 1936, This technique became a major tool in the reconstruction of evolutionary history and was applied to many species by Dobzhansky and by others. A notable example of the success of this method is the reconstruction of the phylogeny of Hawaiian species by Hampton L. Carson and his colleagues.

Originally, Dobzhansky thought that the various chromosomal arrangements of D. pseudoobscura were adaptively equivalent (see the 1941 edition of Genetics and the Origin of Species). and hence that their geographical and temporal variation was the result of genetic drift. Eventually he became convinced that the chromosomal polymorphisms are adaptive, but remained interested in the roles that migration, mutation, and drift play in the maintenance of variation in natural populations.

Estimates of rates of mutation and of accumulation of lethal genes were first published in 1941 (again in collaboration with Sewall Wright); estimates of the critical parameter Nm (the product of effective population size times migration rate) in natural populations appeared in 1942, 1952, and 1954. Dobzhansky developed techniques for the experimental study of migration in nature and published pioneering works in the 1940’s; he returned later to this research and spent most of the last few summers of his life at the cabin of the Carnegie Institution research station in Mather, near Yosemite in the Sierra Nevada, measuring the rates of dispersion in Drosophila.

Dobzhansky early realized the need to investigate the ecological basis of natural variation. He investigated the nutritional preferences first of D. pseudoobscura and later of other species (papers in 1951, 1955, and 1956). Several papers (for instance, 1957, 1959) were devoted to ascertaining—particularly in D. willistoni—the relationships between the ecological diversity of the environment and the degree of genetic polymorphism. He also investigated the physiological basis of adaptation, starting with studies of fecundity and rates of oxygen consumption published in 1935.

Genetic variation is a necessary condition for evolution. Dobzhansky probably dedicated more research effort to the study of genetic variation in natural populations than to any other single problem. He studied morphological variations but saw that physiological variation—variati on affecting fitness— would be most important in evolution. Taking advantage of genetic methods to produce flies homo zygous for full chromosomes, he first investigated the frequency of lethal mutations in nature. In 1942, Dobzhansky published a classical paper showing that variation in fitness is a pervasive phenomenon: Virtually every chromosome found in nature carries genes that are deleterious in the homozygous condition; most individuals in nature are well adapted because they are heterozygous for the deleterious variants— “It is the adaptive level of individuals heterozygous for various chromosomes which is most important” (Genetics, 27 [1942], 487).

Dobzhansky pursued the study of this “concealed variation” affecting fitness for two and a half decades. When the techniques of gel electrophoresis were first applied to population genetics in the mid-1960s, he became quite enthusiastic. He appreciated that these studies made it possible to obtain quantitative measures of genetic variation. He also saw that there is a trade-off between electrophoretic studies and the earlier methods of studying concealed variation: the adaptive role of electrophoretic variation is not immediately apparent.

In the 1940’s Dobzhansky started work with the D. willistoni group of species that resulted in contributions to evolutionary genetics comparable in significance with those derived from the study of D. pseudoobscura and its relatives that he had started in the 1930’s. The most distinctive results with this group concern the process of speciation and concomitant development of reproductive isolation. The willistoni group contains several sibling species. One of these, D.paulistorum, is a cluster of semispecies, or species in statu nascendi, where varying degrees of hybrid sterility, and particularly sexual isolation, can be observed. He discovered and took advantage of this favorable state of affairs for the experimental study of a fundamental evolutionary problem, speciation. He also used D. paulistorum as the organism for laboratory study of sexual isolation by selection. This work brought unsought publicity in such periodicals as the New York Times and Time magazine.

From around 1960 until his death, Dobzhansky worked on the geotactic and phototactic behavior of Drosophila. His interest in this field was only in a small part ascertaining the genetic basis of some simple behavioral traits. His main purpose was, rather, to model the interaction of selection, gene flow, and population size for a behavioral trait with low heritability. There were some unexpected but instructive results, such as the observation of what prima facie appeared to be a case of negative heritability.

Contributions to General Genetics and Other Experimental Work . Dobzhansky made significant contributions to other fields of population biology besides population genetics, particularly to ecology and systematics. Much of his population genetics research had an ecological component: geographical and temporal variation in population characteristics, food resource preferences of Drosophila species, rates of dispersion, ecological diversity of environments, and so on. Among his other ecological investigations, two at least deserve mention. One is the study of species” diversity in tropical forests, which led him to a hypothesis to account for the high level of species diversification in the tropics (1950). Then, in the early 1960’s, he published several papers on the estimation of the innate capacity for increase in numbers in diverse Drosophila populations.

Dobzhansky made significant contributions to “classical” genetics, particularly during the 1920’s and 1930’s. I shall mention but a few. Using translocations between the second and third chromosomes of Drosophila melanogaster, he demonstrated that the linear arrangement of genes based on linkage relationships corresponds to a linear arrangement of genes in chromosomes (1929). This linear correspondence had been postulated before but proof was first provided by Dobzhansky (and independently by Hermann Muller and The ophilus Painter the same year). Also in 1929, Dobzhansky advanced the first sophisticated cytological map of a chromosome— chromosome III of D. melanogaster. He showed that the relative distances between genes are different in the linkage and in the cytological map; genes clustered around the center of the linkage map are spread throughout a larger portion of the cytological map. He correctly inferred that the frequency of crossing over is not evenly distributed throughout the chromosome.

Later, Dobzhansky produced cytological maps of the chromosomes II (1930) and X (1932) of D. melanogaster, and propounded that the centromere (the “spindle fiber attachment,” in the terminology of the time) is a permanent feature of chromosomes. He demonstrated that translocations decrease the frequency of crossing over and advanced a hypothesis to account for this reduction (1931).

Dobzhansky demonstrated that the determination of femaleness by the X chromosome is not due to a single or a few genes, but to multiple factors distributed throughout the chromosome (1931). His publications on the genetic and environmental factors affecting sex determination started in 1928 and extended for more than a decade. These studies included work on bobbed mutants in the Y chromosome and their role in male sterility (1933), as well as numerous publications on gynandromorphs and “superfemales.” His publications on developmental genetics began in 1930 and continued for many years.

Working with D. melanogaster in Filipchenko’s laboratory at the University of Leningrad, Dobzhansky made the first systematic investigation of the pleiotropic, or manifold, effects of genes (1927), a phenomenon that held his interest into the 1940’s. His contributions to the study of position effects started in 1932 and continued for several years (a review in 1936).

One distinctive characteristic of Dobzhansky’s experimental success is that he selected organisms that provided the best materials to investigate the problems that interested him: The biological particularities of D. pseudoobscura and its relatives, and of the D. willistoni group, made possible many of his discoveries. Moreover, he always worked at the highest level of genetic resolution possible at any given time: He took advantage of the early methods of genetic analysis, then of various cytological tools, later of the giant polytene chromosomes, and of the techniques to produce chromosomal homozygotes. When gel electrophoresis was developed. Dobzhansky immediately recognized its enormous potential as a tool to study population genetics problems. He felt that it was too late in his life for him to learn the technique, but encouraged his students and collaborators to use it and collaborated in several projects using it.

Human Evolution, Human Individuality, and the Concept of Race . Dobzhansky extended the synthesis of Mendelism and Darwinism to the understanding of human nature in Mankind Evolving (1962), a book that some consider to be as important as Genetics and the Origin of Species.

Mankind Evolving remains an unsurpassed synthesis of genetics, evolutionary theory, anthropology, and sociology. Dobzhansky stated that human nature has two dimensions: the biological, which mankind shares with the rest of life, and the cultural, which is exclusive to man. These two dimensions result from two interconnected processes, biological evolution and cultural evolution.

The thesis to be set forth in the present book is that man has both a nature and a “history.” Human evolution has two components, the biological or organic, and the cultural or superorganic. These components are neither mutually exclusive nor independent, but interrelated and interdependent. Human evolution cannot be understood as a purely biological process. nor can it be adequately described as a history of culture. It is the interaction of biology and culture. There exists a feedback between biological and cultural processes (Mankind Evolving, p.18).

Two principal topics of Mankind Evolving are the interrelated concepts of human diversity and race. Dobzhansky’s first major publication on these topics was Heredity, Race, and Society (1946), a book written with Leslie C. Dunn that was translated into many languages and sold more than one million copies. The two topics are the main subject of Genetic Diversity and Human Equality (1973), the last of Dobzhansky’s books published before his death, (Dobzhansky left the completed manuscript for another book, Evolution, written with Francisco J. Ayala, G. Ledyard Stebbins. and James W. Valentine, which appeared in 1977.)

Dobzhansky set forth that the individual is not the embodiment of some ideal type or norm but, rather, a unique and unrepeatable realization in the field of quasi-infinite possible genetic combinations. The pervasiveness of genetic variation provides the biological foundation of human individuality and leads to demystification of the much-abused concept of race. Dobzhansky emphasized that populations or groups of populations differ from each other in the frequencies of some genes. These differences may be recognized by distinguishing populations of a given species as races. Thenumber of races and the boundaries between them are largely arbitrary because rarely, if ever, are populations of the same species separated by sharp discontinuities in their genetic makeup. Most important is the fact that races are polymorphic for the same genetic variants that may be used to distinguish one race from another. There is more genetic variation within any human race than there are genetic differences between races. It follows, as Dobzhansky saw it, that individuals should be evaluated by what they are, not by the race to which they belong.

Dobzhansky considered human diversity a fact belonging to the realm of observable natural phenomena; “People are innately, genetically, and therefore irremediably diverse and unlike” (Genetic Diversity and Human Equality, p. 4). Biological distinctiveness is not, however, a basis for inequality. Equality—as in equality before the law and equality of opportunity— “pertains to the rights and the sacredness of life of every human being” (ibid.) Dobzhansky pointed out that equality of opportunity is the best strategy to maximize the benefits of human biological diversity. “Denial of equality of opportunity stultifies the genetic diversity with which mankind became equipped in the course of its evolutionary development. Inequality conceals and stifles some people’s abilities and dissembles the lack of abilities in others. Conversely equality permits an optimal utilization of the wealth of the gene pool of the human species” (Mankind Evolving, p. 285) Dobzhansky had little patience with racial prejudice or social injustice, and castigated those who pre tended to base them on what he called the “bogus’ science’ of race prejudice.’

Dobzhansky’s lasting interest in the relevance of biology, and particularly evolutionary theory, to human affairs is evident in scores of articles that he wrote on the subject and in the titles of some of his books: Heredity, Race, and Society (1946): Evolution, Genetics, and Man (1955); The Biological Basis of Human Freedom (1956): Radiation, Genes, and Man (1959, with B. Wallace); Mankind Evolving (1962); Heredity and the Nature of Man (1964); The Biology of Ultimate Concern (1967); and Genetic Diversity and Human Equality (1973).

Humanism . Dobzhansky’s interest in the interface between biology and human problems was expressed in numerous publications that, beginning in the mid1940’s, flowed in a continuous stream. His concern was probably kindled by several convergent influences. One factor was the racial bigotry that helped to trigger World War II in Europe; another, Lysenko’s suppression of genetics and geneticists in the Soviet Union; a third, his association with Leslie C. Dunn, a colleague at Columbia University and intimate friend, whose compassion for the human predicament was much revered by Dobzhansky, and who became greatly involved in providing shelter in the United States for scientists fleeing from Nazi persecution.

As mentioned above, Dobzhansky published Heredity, Race, and Society with Dunn in 1946, and continued publishing on race questions from a biological perspective until the end of his life. Publications criticizing eugenic movements appeared in 1952 and 1964; the subject of eugenics was treated in other papers and several books. In 1946 he translated Lysenko’s Heredity and Its Variability into English as a way to expose Lysenko’s quackery. Dobzhansky criticized Lysenko’s “science,” and particularly his eradication of genetics and geneticists, in several articles published between 1946 and 1958.

Dobzhansky was concerned with the role of religion in human life and explored the evolutionary basis of religion in several articles published in the 1960’s and 1970’s, and in his The Biology of Ultimate Concern (1967). Yet he did not hesitate to criticize (1953) the antievolutionist stand of Pope Pius XII in the encyclical Humani generis, or that of fundamentalist Protestants (1973).

Dobzhansky often expressed his frustration at the limited influence of biology on the thinking of philosophers. He saw that evolutionary biology raises new philosophical problems and throws light on old ones. He wrote several essays on philosophical questions, such as the concepts of determinism and chance (1963, 1966, 1974), transcendent phenomena (1965, 1967, 1977), organismic or compositionist approaches in the philosophy of biology (1967, 1968), and the “creative” character of biological evolution (1954, 1967, 1974),

BIBLIOGRAPHY

I. Original Works. A bibliography of Dobzhansky’s publications follows Francisco J. Ayalas memoir in Biographical Memoirs, National Academy of Sciences, 55 (1985), 163–213. A bibliography covering Dobzhansky’s publications from 1918 to 1969 is in Howard Levene, Lee Ehrman, and Rollin Richmond. Theodosius Dobzhansky up to Now,” in Max K. Hecht and William C. Steere, eds., Essays in Evolution and Genetics in Honor of Theodosius Dobzhansky (New York, 1970), 1–41 accompanied by a very brief description of Dobzhansky’s scientific work: the bibliography is fairly complete, although there are a few omissions and errors. The same bibliography, with a career summary and supplemented up to 1976, is in Evolutionary Biology, 9 (1976), 409–448, Papers published between 1938 and 1976 by Dobzhansky and collaborators under the general title “Genetics of Natural Populations” have been reprinted in R. C. Lewontin, John A. Moore, William B. Provine, and Bruce Wallace, eds., Dobzhansky’s Genetics of Natural Populations I-XLIII (New York, 1981), which contains introductions about Dobzhansky’s scientific work by Provine and Lewontin.

Dobzhansky’s books include Genetics and the Origin of Species (New York, 1937; 2nd ed., 1941; 3rd ed., rev., 1951); Heredity Race, and Society (New York, 1946; 2nd ed., 1952; 3rd ed., rev and enl., 1956), written with Leslie C. Dunn; Principles of Genetics (4th ed., New York, 1949; 5th ed., 1958) written with Edmund W. Sinnott and Leslie C. Dunn (Dobzhansky was not a coauthor of the first three editions of this book); Evolution, Genetics, and Man (New York, 1955); The Biological Basis of Human Freedom (New York, 1956); Radiation, Genes, and Man (New York, 1959), written with B. Wallace; Mankind Evolving: The Evolution of the Human Species (New York, 1962); Heredity and the Nature of Man (NewYork, 1964); The Biology of Ultimate Concern (New York. 1967); Genetics of the Evolutionary Process (New York, 1970); Genetic Diversity and Human Equality (New York, 1973); Evolution (San Francisco, 1977), written with Francisco J. Ayala, G. Ledyard Stebbins, and James W. Valentine; and The Roving Naturalist, Travel Letters of Theodosius Dobzhansky, Bentley Glass, ed, (Philadelphia, 1980).

Dobzhansky’s articles include “Description of a New Species of the Genus Coccinella from the Neighbourhood of Kiev,” in Materialy dlia fauny iugozapadnoi Rossii, 2 (1918), 46–47 (in Russian); “Die geographische und individuelle Variabilität von Harmonia axyridis Pallas in ihren Wechselbeziehungen,” in Biologisches Zentralblatt, 44 (1924), 401 -421; “Die weiblichen Generationsorgane der Coccinelliden als Artmerkmal betrachtet (Coleoptera),” in Entomologische Mitteilungen, 13 (1924), 18–27; “Beitrag zur Kenntnis des weiblichen Geschlechtsapparates der Coccinelliden,” in Zeitschrift für wissenschaftliche Insektenbiologie, 19 (1924), 98–100; “Studies on the Manifold Effect of Certain Genes in Drosophila melanogaster,” in Zeitschrift für induktive Abstammungsund Vererbungslehre, 43 (1927), 330–388; “The Effect of Temperature on the Viability of Superfemales in Drosophila melanogaster.” in Proceedings of the National Academy of Sciences, 14 (1928), 671–675; “The Reproductive System of Triploid Intersexes in Drosophila melanogaster,” in American Naturalist, 62 (1928), 425–434, written with C B. Birdges. “Genetical and Cytological Proof of Translocations Involving the Third and the Fourth Chromosomes of Drosophila melanogaster,” in Biologische Zentralblatt, 49 (1929), 408–419; “A Homozygous Translocation in Drosophila melanogaster,” in Proceedings of the National Academy of Sciences, 15 (1929), 633–638.

“Genetical and Environmental Factors Influencing the Type of Intersexes in Drosophila melanogaster,”in American Naturalist 64 (1930), 261–271; “Cytological Map of the Second Chromosome of Drosophila melanogaster,” in Biologische Zentralblatt, 50 (1930), 671–685; “Interaction Between Female and Male Parts in Gynandromorphs of Drosophila simulans,” in Zeitschrift für Wissenschaftliche Biologie, Abt. D. Wilhelm roux’ Archiv für Entwicklungsmechanik der Organismen, 123 (1931) 719–746; “The Decrease of Crossing-over Observed in Translocations, and Its Probable Explanation,” in American Naturalist65 (1931), 214–232; “Evidence for Multiple Sex Factors in the X-Chromosome of Drosophila melanogaster,” in Proceedings of the National Academy of Sciences, 17 (1931), 513–518, written with J. Schulte.

Cytological Map of the X-Chromosome of Drosophila melanogaster,” in Biologische Zentralblatt, 52 (1932). 493–509; “Geographical Variation in Lady-Beetles,” in American Naturalist, 67 (1933), 97–126; “On the Sterility of the Interracial Hybrids in Drosophila pseudoobscura,” in Proceedings of the National Academy of Sciences, 19 (1933), 397–403; “Role of the Autosomes in the Drosophila pseudoobscura Hybrids,” ibid., 950–953; “Deficiency and Duplication for the Gene “Bobbed” in Drosophila melanogaster,” in Genetics, 18 (1933). 173–192, written with Natalia P. Sivertzev-Dobzhansky; “A Critique of the Species Concept in Biology,” in Philosophy of Science2 (1935), 344–355: “Oxygen Consumption of Drosophila Pupae. II. Drosophila pseudoobscura,” in Zeitschrift für Vergleichende Physiologie,” 22 (1925), 473–478, written with D. F. Poulson; “Position Effects of Genes,” in Biological Reviews, 11 (1936), 364–384: “Inversions in the Third Chromosome of Wild Races of Drosophila pseudoobscura, and Their Use in the Study of the History of the Species,” in Proceedings of the National Academy of Sciences, 22 (1948), 448–450, written with Alfred H. Sturtevant: “Genetic Nature of Species Differences,” in American Naturalist, 71 (1937) 404–420; “Genetics of Natural Populations. I. Chromosome Variation in Populations of Drosophila pseudoobscura Inhabiting Isolated Mountain Ranges,” in Genetics, 23 (1938), 239–251, written with M. L. QueaL “Genetics of Natural Populations. V. Relations Between Mutation Rate and Accumulation of Lethals in Populations of Drosophila pseudoobscura,” in Genetics, 26 (1941), 23–51, written with Sewall Wright; “Beetles of the Genus Hyperaspis Inhabiting the United States’s in Smithsonian Institution Publication no, 3642 (1941) 1–94, “Genetics of Natural Populations. VII. The Allelism of Lethals in the Third Chromosome of Drosophila pseudoobscura,” in Genetics, 27 (1942), 363–394, written with Sewall Wright and W. Hovanitz; “Genetics of Natural Populations. VIII. Concealed Variability in the Second and Fourth Chromosomes of Drosophila pseudoobscura and Its Bearing on the Problem of Heterosis,” ibid., 27 (1942), 464–490, written with A.M. Holz and Boris Spassky; “’Genetics of Natural Populations. IX Temporal Changes in the Composition of Populations of Drosophila pseudoobscura,” ibid., 28 (1943), 162–186; “Genetics of Natural Populations. XII, Experimental Reproduction of Some of the Changes Caused by Natural Selection in Certain Populations of Drosophila pseudoobscura,” ibid., 31 (1946). 125–156, written with Sewall Wright, “Lysenko’s’ Genetics,” in Journal of Heredity. 37 (1946), 5–9; “The New Genetics in the Soviet Union,” in American Naturalist, 80 (1946), 649–651; “The Suppression of a Science,” in Bulletin of the Atomic Scientists, 5 (1949), 144–146.

“Evolution in the Tropics,” in American Scientist, 38 (1950), 209–221; “A Comparative Study of Chromosomal Polymorphism in Sibling Species of the willistoni Group of Drosophila,” in American Naturalist, 84 (1950), 229–246, written with H. Burla and Antonio Brito da Cunha; “Comparative Genetics of Drosophila willistoni,” in Heredity, 4 (1950), 201–215, written with Boris Spassky; “Some Attempts to Estimate Species Diversity and Population Density of Trees in Amazonian Forests,” in Botanical Gazette, 111 (1950), 413–524, written with G. Black and C. Pavan; Adaptive Chromosomal Polymorphism in Drosophila willistoni” in Evolution, 4 (1950), 212–235, written with Antonio Brito da Cunha and H. Burla. “On Food Preferences of Sympatric Species of Drosophila,” ibid., 5 (1951 ), 97–101, written with Antonio Brito da Cunha and A. Sokoloff; “Genetics of Natural Populations. XX, Changes Induced by Drought in Drosophila pseudoobscura and Drosophila persimilis,” ibid., 6 (1952), 234–243; “Lysenko’s’ Michurinist Genetics,” in Bulletin of the Atomic Scientists, 8 (1952), 40–44; “A Comparative Study of Mutation Rates in Two Ecologically Diverse Species at Drosophila,” Genetics, 37 (1952), 650–664, written with Boris Spassky and N. Spassky; “Two Recent Versions of Eugenics,” in American Naturalist, 86 (1952), 61–62; “Russian Genetics,” Ruth C. Christman, ed., Soviet Science (Washington, D.C. 1952), 1–7; “A Comment on the Discussion of Genetics by His Holiness, Pius XII,” in Science. 118 (1953), 561–563; “Evolution as a Creative Process,” in Atti del IX Congresso internazionale di genetica, Pt 1, which is supp, to Caryologia, 6 (1954), 435–449; “Rates of Spontaneous Mutation in the Second Chromosomes of the Sibling Species, Drosophila pseudoobscura and Drosophila persimilis in Genetics, 39 (1954), 899–907, written with Boris Spassky and N. Spassky; “Differentiation of Nutritional Preferences in Brazilian Species of Drosophila,” in Ecology, 36 (1955), 34–39, written with Antonio Brito da Cunha; “Studies on the Ecology of Drosophila in the Yosemite Region of California. IV. Differential Attraction of Species of Drosophila to Different Species of Yeasts,” ibid., 37 (1956), 544–550, written with D. M. Cooper. H. J. Phaff, E. P. Knapp, and H. L. Carson; “Genetics of Natural Populations, XXVI, Chromosomal Variability in Island and Continental Populations of Drosophila willistoni from Central America and the West Indies,” in Evolution11 (1957), 280–293; “Lysenko at Bay,” in Journal of Heredity, 49 (1958), 15–17; “Genetics of Natural Populations, XXVIII. Supplementary Data on the Chromosomal Polymorphism in Drosophila willistoni in Its Relation to the Environment,” ibid., 13 (1959), 389–404, written with Antonio Brito da Cunha, Olga Pavlovsky, and Boris Spassky; “Drosophila paulistorum, a Cluster of Species in Statu Nascendi,” in Proceedings of the National Academy of Sciences, 45 (1959), 419–428, written with Boris Spassky.

“Selection for Geotaxis in Monomorphic and Polymorphic Populations of Drosophila pseudoobsucra,” ibid., 48 (1962), 1704–1712, written with Boris Spassky; “Scientific Explanation; Chance and Antichance in Organic Evolution,” in Bernard Baumrin, ed., Philosophy of Science, I (New York, 1963), 209–222; “Relative Fitness of Geographic Races of Drosophila serrata,” in Evolution, 17 (1963), 72–83, written with L. C. Birch, P. O. Elliot, and R. C. Lewontin; “Human Genetics—an Outsider’s View,” in Cold Spring Harbor Symposia in Quantitative Biology, 29 (1964), 1–7: “The Superspecies Drosophila paulistorum,” in Proceedings of the National Academy of Sciences, 51 (1964), 3–9, written with Lee Ehrman, Olga Pavlovsky, and Boris Spassky: “The Capacity for Increase in Chromosomally Polymorphic and Monomorphic Populations of in Drosophila willistoni,” in Heredity, 19 (1964), 597–614. written with R. C. Lewontin and Olga Pavlovsky; “Evolution and Transcendence,” in Main Currents in Modern Thought22 (1965), 3–9; “Determinism and Indeterminism in Biological Evolution,” In Vincent E. Smith, ed., Philosophical Problems in Biology (New York, 1966), 55–56; “Spontaneous Origin of an Incipient Species in the Drosophila paulistorum complex,” in Proceedings of the National Academy of Sciences, 55 (1966), 727–733, written with Olga Pavlovsky; “Creative Evolution,” in Diogenes, 58 (1967), 62–74; “Effects of Selection and Migration on Geotactic and Phototactic Behaviour of Drosophila. I,” in Proceedings of the Royal Society, B168 (1967), 27–47, written with Boris Spassky; “On Some Fundamental Concepts of Darwinian Biology/’ in Evolutionary Biology, 2 (1968), 1–34.

“Polymorphisms in Continental and Island Populations of Drosophila willistoni,” in Proceedings of the National Academy of Sciences, 68 (1971), 2480–2483; written with Francisco J. Ayala and Jeffrey R. Powell; “Genetics and the Diversity of Behavior,” in American Psychologist, 27 (1972), 523–530; “Effects of Selection and Migration on Geotactic and Phototactic Behaviour of Drosophila, III,” in Proceedings of the Royal Society, B180 (1972), 21–41, written with Howard Levene and Boris Spassky; “Temporal Frequency Changes of Enzyme and Chromosomal Polymorphisms in Natural Populations of Drosophila,” in Proceedings of the National Academy of Sciences, 70 (1973), 680–683, written with Francisco J. Ayala; “Nothing in Biology Makes Sense Except in the Light of Evolution,” in American Biology Teacher, 35 (1973), 125–129; “Chance and Creativity in Evolution,” in F. J. Ayala and Theodosius Dobzhansky, eds., Studies in the Philosophy of Biology (London, 1974), 307–338; and Humankind—A Product of Evolutionary Transcedence (Johannesburg, 1977), written with Francisco J. Ayala.

II. Secondary Literature. Dobzhansky’s work is reflected in Hampton L. Carson. D. Elmo Hardy, Herman T. Spieth and Wilson S. Stone. “The Evolutionary Biology of the Hawaiian Drosophilidae,” in Max K. Hecht and William C. Steere, eds., Essays in Evolution and Genetics in Honor of Theodosius Dobzhansky (New York, 1970), 437–543; Julian S. Huxley, Evolution: The Modern Synthesis (New York, 1942; repr. 1964); Ernst Mayr, Systematics and the Origin of Species (New York, 1942); George G. Simpson, Tempo and Mode in Evolution (New York, 1944); G. Led yard Stebbins, Variation and Evolution in Plants (New York, 1950).

Francisco J. Ayala

Dobzhansky, Theodosius 1900-1975

BIBLIOGRAPHY

Theodosius Dobzhansky, born in the town of Nemirov in the Ukraine on January 25, 1900, was one of the most influential biologists of the twentieth century. He is generally regarded as the pioneer of evolutionary genetics, a field established in the 1930s that sought to integrate Darwinian selection theory with Mendelian genetics. Much of this work was summarized in Dobzhansky’s magnum opus, Genetics and the Origin of Species, published in 1937. It was so influential and widely read that it is regarded as the first “textbook” of evolutionary biology in the twentieth century.

The only child of Sophia Voinarsky and Grigory Dobrzhansky, a high-school mathematics teacher, Dobzhansky early on manifested an interest in natural history and collected insects and especially butterflies in the area of Kiev. He attended the University of Kiev and graduated in 1921 with a major in biology. He subsequently accepted a position on the faculty of agriculture at the Polytechnic Institute of Kiev, where, through the influence of plant geneticist Gregory Levitsky, Dobzhansky’s interests shifted from the systematics of insects like the ladybird beetle (the Coccinelidae ) to the newer areas of genetics. Levitsky was part of a wider scientific movement in the Soviet Union that included such individuals as Nikolai Ivanovich Vavilov (1887–1943) and Sergei Chetverikov (1880–1959). These scientists were following efforts in American genetics to understand the mechanism of Mendelian heredity through model organisms, such as the fruit fly (Drosophila sp.). In 1924 Dobzhansky moved to Leningrad (Saint Petersburg), where he became a lecturer in genetics under the wing of Yuri Filipchenko and where he continued to study genetics by turning to basic laboratory studies of Drosophila melanogaster. At this time, he married a coworker in genetics, Natalie (or “Natasha”) Sivertsev, who was to be his lifelong companion and coworker; they had one daughter, Sophie.

In 1927 Dobzhansky accepted a fellowship from the Rockefeller Foundation to study genetics with the American leader in the area, Thomas Hunt Morgan (1866–1945), and his group of fly geneticists at Columbia University, a group that included A. H. Sturtevant (1891–1970), Calvin Bridges (1889–1938), and H. J. Muller (1890–1967). While working as an assistant to Morgan, Dobzhansky learned of the latest techniques and insights into understanding the cytogenetics of the fruit fly. In 1928 Dobzhansky moved to the California Institute of Technology with Morgan and subsequently became assistant professor of genetics in 1929.

Dobzhansky’s most notable breakthrough was made in 1933 when he started working with the geographically diverse Drosophila pseudoobscura. He also began to combine the laboratory methods common to the Morgan group with his interests in systematics and biogeography, which reflected his earlier Russian training. His research into the evolutionary history of this complex group of flies was aided by his novel use of the giant salivary or polytene chromosome, which permitted the reconstruction of the phylogenetic history of the model organism. This research formed the backbone of what became known as the genetics of natural populations (GNP) series, a set of studies published as papers and monographs that explored the range of species, races, and varieties of this group of flies and that sought to understand the process of speciation in genetic terms. It also informed Dobzhansky’s 1937 book, his increasing independence from Morgan’s fly group, and his interaction with American mathematical theorist Sewall Wright (1889–1988).

By the late 1930s Dobzhansky was recognized as one of the central figures in the “new” or “modern” synthesis of evolution that integrated Darwinian selection theory and natural history with laboratory methods and insights gleaned from Mendelian genetics. Dobzhansky increasingly drew younger workers to him, and developed an international reputation for being a “charismatic” mentor.

In 1940 he accepted a position at Columbia University, where he continued his research on Drosophila. In the 1950s his interests took a more global direction when he traveled to South America to study the speciation patterns in tropical Drosophila. In 1962 he moved yet again to Rockefeller University, where he remained until his retirement in 1970.

Dobzhansky’s interests were broad and included the application of genetics to evolution and to the understanding of human beings. He wrote extensively, especially in his later years, on subjects with anthropological and philosophical themes. His synthesis of evolution and cultural anthropology appeared in 1962 under the title Mankind Evolving. In 1967 he revealed his lifelong interest in the existential aspects of evolution and in traditional religious concerns in The Biology of Ultimate Concern.

Becoming one of the most famous Soviet émigrés in the United States, Dobzhansky closely monitored the progress of science in the Soviet Union and was especially active in campaigning against biologist Trofim Lysenko (1898–1976) and his destructive policies against Soviet genetics. Despite his feeling a strong connection to his first home, Dobzhansky was never allowed to return there.

Following his retirement, Dobzhansky moved to the University of California in Davis, where he continued to supervise an active group of geneticists. He died there on December 18, 1975, after a long battle with leukemia. Although he was closely associated with the newer evolutionary biology of the twentieth century, he remained fundamentally religious and was an active member of the Russian Orthodox Church.

SEE ALSO Racial Classification

BIBLIOGRAPHY

Adams, Mark B. 1994. The Evolution of Theodosius Dobzhansky: Essays on His Life and Thought in Russia and America. Princeton, NJ: Princeton University Press.

Ayala, Francisco J. 1985. Theodosius Dobzhansky. Biographical Memoirs National Academy of Sciences 55: 163–213.

Levene, Howard, Lee Ehrman, and Rollin Richmond. 1970. Theodosius Dobzhansky Up to Now. In Essays in Evolution and Genetics in Honor of Theodosius Dobzhansky, eds. Max K. Hecht and William C. Steere, 1–41. New York: AppletonCentury Crofts.

Levine, Louis, ed. 1995. Genetics of Natural Populations: The Continuing Importance of Theodosius Dobzhansky. New York: Columbia University Press.

Lewontin, R. C., John A. Moore, William B. Provine, and Bruce Wallace, eds. 1981. Dobzhansky’s Genetics of Natural Populations I-XLIII. New York: Columbia University Press.

Vassiliki Betty Smocovitis

Theodosius Dobzhansky

Theodosius Dobzhansky (1900-1975) synthesized field study and laboratory experimentation in the study of natural selection, laying a foundation for Darwinian evolutionary theory.

Few biologists have made more important contributions to 20th-century evolutionary theory than Theodosius Dobzhansky. His work represents a major part of the synthesis of field study, laboratory experimentation, and classical Mendelian theory that became a powerful foundation for Darwinian theory. Dobzhansky's writings were prolific and influential, comprising over 550 papers and some dozen books. He wrote not only about the technical details of evolution in natural populations, but also about the social and philosophical sides of evolution— including the future evolution of the human species. He lived according to his own dictum, the title of a paper in 1972: "Nothing in biology makes sense except in the light of evolution."

Born on January 25, 1900, in Nemirov, Russia, a small town 200 kilometers southeast of Kiev in the Ukraine, Dobzhansky was the only child of Sophia Voinarsky and Grigory Dobzhansky (sic, the precise transliteration of the Russian name), a high school mathematics teacher. An avid butterfly collector, young Dobzhansky decided to become a biologist at about the age of 12. The family lived on the outskirts of Kiev during the tumultuous years of World War I and the Bolshevik Revolution. During this period Dobzhansky managed to complete his high school and university studies, graduating with a degree in biology from the University of Kiev in 1921.

As an instructor in zoology at the Polytechnic Institute in Kiev (1921-1924), he met Yuri Filipchenko, head of the newly-created Department of Genetics at the University of Leningrad and a strong advocate of T. H. Morgan's work at Columbia University in New York with the small fruit fly, Drosophila melanogaster. Dobzhansky went to work in Filipchenko's lab in 1924, where he began his first studies in genetics. In that same year he married Natalia Sivertzev, a geneticist in her own right working with the famous Russian evolutionist I. I. Schmalhausen in Kiev.

In 1927 Dobzhansky travelled to the United States under the auspices of a fellowship from the International Education Board (Rockefeller Foundation) to work in Morgan's laboratory at Columbia University. Here he began learning the techniques of cytogenetics, particularly the study of chromosome banding structures, that were to be so valuable in his later field studies of evolution in the wild Drosophila population. In September 1928 Dobzhansky moved to the California Institute of Technology, where Morgan had gone to organize and direct the newly-created division of biology. Dobzhansky was named assistant professor of genetics at Caltech in 1929 and professor in 1936. In 1940 he returned to New York as professor of zoology at Columbia University, where he remained for the next 22 years. In 1962 Dobzhansky was appointed professor at the Rockefeller Institute (now Rockefeller University), and in 1971 adjunct professor in the Department of Genetics at the University of California, Davis, a position he held until his death on December 18, 1975.

Dobzhansky's contributions to evolutionary theory relate to five major issues: the amount of variation that exists in natural populations; genetic changes in wild populations due to natural selection; speciation; laboratory studies of fitness under controlled conditions; and human variation and evolution.

Genetic Variation Studies

When Dobzhansky came to the United States in 1927 the predominant view of genetic variation was that established by the work of T. H. Morgan and H. J. Muller in mutant laboratory stocks. Mutations were thought to be relatively rare and other variations in most cases deleterious. Since an organism's overall genetic make-up was the result of natural selection, with deleterious mutations weeded out, wild populations were assumed to harbor few mutations, or variations. As a result, evolution would be— as this was in line with what Darwin had predicted—a relatively slow process.

One of Dobzhansky's major contributions was to show that this view was incorrect. Applying the cytological methods of the Morgan group to the analysis of chromosome structure in wild populations of Drosophila pseudoobscura, Dobzhansky discovered a surprising amount of hidden variability—that is, variations not readily observed in the appearance of individual organisms. Dobzhansky suggested that preservation of extensive variation would allow populations to evolve rapidly as environmental conditions change. Dobzhansky published his findings in Genetics and the Origin of Species in 1937. This book was an important landmark in the evolutionary synthesis: the union of Mendelian genetics and Darwinian theory.

In Morgan's laboratory at Caltech Dobzhansky learned the cytological techniques involved in studying chromosome structure from two of Morgan's most important coworkers, A. H. Sturtevant and C. B. Bridges. In the mid-and late-1930s he had collaborated with Sturtevant on a series of papers using chromosome inversions (where a chromosome segment has been accidentally excised and reinserted in the chromosome upside down) as a way of tracing phylogenetic relationships among species and subspecies of Drosophila. Since inversions are inherited, two separate populations of varieties that showed similarities in chromosome inversion patterns ought to be more closely related than one having fewer similarities.

This work led to a subsequent series of papers of great importance. In the early and mid-1940s, Dobzhansky examined chromosome inversion patterns in populations of Drosophila pseudoobscura from Santa Barbara to central Texas. Each population, he found, had a different frequency for each of several inversion patterns. Moreover, noting that from one season to the next certain inversion patterns increased and others decreased within the same population, Dobzhansky correlated these changes with climatic and other environmental differences associated with changing seasons. He found that one inversion pattern predominated during warmer seasons, while another predominated during colder seasons. Bringing samples from each population back into the laboratory, Dobzhansky showed that he could vary environmental conditions so as to produce the same changes in frequency of inversion patterns that were observed with changing seasons in the field. Dobzhansky concluded that such seasonal fluctuations were the result of natural selection at work, with temperature acting as the selecting agent. These masterful studies provided concrete support for the theory of natural selection, at the same time illustrating the fruitfulness of combining field and laboratory work in the study of evolution.

Speciation and Evolution

As part of the larger question of how speciation occurs, Dobzhansky initiated a number of investigations into the basis of hybrid sterility—that is, the inability of the offspring of many hybrids (especially among animals) to be reproductively fertile. By studying the specifics of sexual, physiological, and behavioral isolating mechanisms in Drosophila pseudoobscura and Drosophila paulistrorum, Dobzhansky showed that varying degrees of reproductive isolation represented speciation in the process. Like many of his other studies, Dobzhansky's work on reproductive isolation was aimed at studying the process of evolution in action.

Although not primarily a human geneticist or paleontologist, Dobzhansky wrote frequently on human evolution, including the biology of race and the future of human evolution. His Mankind Evolving of 1962 was a highly influential work in directing attention to human variation and adaptation. Several subsequent works of a similar nature, such as The Biological Basis of Human Freedom (1956), The Biology of Ultimate Concern (1967), and Genetics of the Evolutionary Process (1970), all reflect Dobzhansky's wide-ranging and philosophical turn of mind.

Although plagued by a form of leukemia in his later years, Dobzhansky remained vigorous and active until the day before his death on December 18, 1975. During his lifetime he was the recipient of many honors and awards. He was a member of the U.S. National Academy of Sciences, the American Academy of Arts and Sciences, the American Philosophical Society, the Royal Society (Great Britain), the Academia Leopoldina (Leipzig), and the Academia Nazionale dei Lincei (Florence). He received the Daniel Giraud Elliot Medal (1946) and the Kimber Genetics Award (1958) from the National Academy of Sciences, the Darwin Medal from the Leopoldina (1959), the A. E. Verrill Award from Yale University (1966), the Gold Medal Award for Distinguished Achievement in Science from the American Museum of Natural History (1969), and the National Medal of Science (1964). In addition, Dobzhansky was awarded honorary degrees by over 20 institutions, including the Universities of São Paulo (Brazil), Münster (Germany), Sydney (Australia), Oxford (England), Padua (Italy), and Chicago, Columbia, Michigan, Syracuse, Berkeley, and Northwestern in the United States.

Further Reading

A detailed biography of Dobzhansky has been prepared by Howard Levene, Lee Ehrman, and Rollin Richmond, "Theodosius Dobzhansky up to now," in Max Hecht and William C. Steere (editors), Essays in Evolution and Genetics in Honor of Theodosius Dobzhansky (1970). A shorter appreciation was written by Francisco Ayala, "'Nothing in biology makes sense except in the light of evolution.' Theodosius Dobzhansky, 1900-1975," in Journal of Heredity (1977). Two important historical essays appear in the reprinted edition of Dobzhansky's "The Genetics of Natural Populations" Series: Richard Lewontin, "Introduction: the scientific work of Th. Dobzhansky," and William B. Provine, "Origins of the 'Genetics of Natural Population' series," in R. C. Lewontin, John A. Moore, William B. Provine, and Bruce Wallace (editors), Dobzhansky's Genetics of Natural Populations I-XLIII (1981). This work contains a complete bibliography. □

Dobzhansky, Theodosius (1900–75) US geneticist and authority on human evolution, b. Russia. He was influential in the development of population genetics as a separate study. His writings include Genetics and the Origin of Species (1937), Mankind Evolving (1962), and Genetics of the Evolutionary Process (1970).