Simpson, George Gaylord

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(b. Chicago, Illinois, 16 June 1902; d. Tucson, Arizona, 6 October 1984),

paleontology, vertebrate paleontology.

Simpson was an empirical paleontologist specializing in mammals; he led numerous expeditions to discover new fossils. These were described and analyzed in hundreds of technical publications. However, Simpson is best known for incorporation of evidence from fossils and earth history in understanding biological systematics and evolution. Simpson was a principal architect of the “modern synthesis” of evolutionary thought emerging in the 1940s.

Early Life and Education Simpson’s father, Joseph Alexander Simpson, was a successful attorney, first in Chicago and then in the frontier mining and railway city of Denver, Colorado. There he took advantage of opportunities for land development and then mining. Simpson’s mother, Helen Kinney, lost her own mother at a young age and was raised in Hawaii by grandparents who were Presbyterian missionaries there. George Gaylord Simpson was the third of three children. He had two sisters, Margaret and Martha, who were seven and four years older, respectively. The family was Presbyterian, but Simpson himself was never particularly religious.

Simpson grew up in Denver, in a Rocky Mountain environment where he enjoyed nature with family and friends. He credited camping, mountain climbing, and mining with his father for inspiring an interest in geology. These experiences made him comfortable outdoors, where he was to spend many months of his adult life. Looking back as an adult, Simpson felt that certain of his boyhood characteristics—his intelligence, shortness of stature, red hair, and visual impairment that limited ball playing— combined to foster antagonism from his peers. Serious and studious, Simpson advanced rapidly through school in spite of occasional setbacks due to health. He entered the University of Colorado at Boulder when he was age sixteen.

At the University of Colorado, Simpson was influenced by Arthur J. Tieje, who introduced him to the excitement and mystery of historical geology and paleontology, subjects that would inspire a lifetime of intensely focused scholarship. When Tieje left Colorado, he advised Simpson to transfer to Yale University as the best place to study paleontology. Simpson transferred in 1922, finished his AB degree in 1923 at Yale, and entered graduate school there to pursue a career in paleontology.

Soon after moving east, Simpson secretly married Lydia Petroja while he was still an undergraduate. Four daughters, Helen, Patricia (Gay), Joan, and Elizabeth, were born in the next six years, but the marriage ended in separation and divorce. In 1938 Simpson married again, this time to psychologist Anne Roe, a childhood friend from Denver. Simpson and Roe remained married until Simpson’s death forty-six years later.

At Yale, Simpson found a large and little-studied collection of North American Mesozoic mammals that he analyzed for his PhD. The Mesozoic Era in Earth history is popularly known as the age of dinosaurs, but it is also the time when mammals began their early diversification. Humanity’s history as mammals is deeply rooted in the Mesozoic, and it was natural that Simpson would seek to learn all he could of Mesozoic mammals. The dissertation was completed and the degree awarded in 1926. Simpson immediately moved to the British Museum of Natural History in London as a postdoctoral scholar to undertake a similar study of European Mesozoic mammals. The two resulting monographs— A Catalogue of the Mesozoic Mammalia in the Geological Department of the British Museum(1928) and “American Mesozoic Mammalia” (1929) established Simpson as a precocious but surprisingly mature authority on early mammal diversification and evolution.

Museum Work Returning from Europe in 1927, Simpson joined the American Museum of Natural History in New York as an assistant curator. He continued research on early mammals but moved up stratigraphically and forward in time to study the beginning of the major Cenozoic diversification of mammals. He worked first on North American faunas and in 1932 was invited to study a major collection of Paleocene mammals at the National Museum of Natural History in Washington, D.C. This required fieldwork in the Crazy Mountains Basin of central Montana to collect more specimens and determine their stratigraphic context. Samples for some species were large, requiring statistical characterization for diagnosis and comparison as once-living populations. The Crazy Mountains study, more than any of his previous works, enabled Simpson to quantify and compare evolutionary change through time, and it required implementation of a rational taxonomic framework capable of encompassing history. Simpson emphasized quantification and stratigraphy in a way that soon led to introduction of chronoclines as a way of quantifying how morphology changes through time (analogous to the spatial clines that quantify how morphology changes geographically).

Simpson’s curiosity about extinct mammals went beyond those known from North America, and in the 1930s he initiated two major paleontological field expeditions to Patagonia, the first in 1930–1931 and the second in 1933–1934. The purpose was to characterize the history of South American mammals evolving in isolation from the rest of the world. His popular journal of these expeditions, Attending Marvels (1934), has been read by many and reprinted several times. Research in Patagonia led to many publications summarized in a major systematic review, Beginning of the Age of Mammals in South America (1948), published in two parts over the course of two decades (part 2 appeared in 1967). Fieldwork in Patagonia initiated a lifelong interest in penguins, with a parallel series of publications on penguin fossils and evolution.

At the American Museum, Simpson worked tirelessly, publishing hundreds of technical reports and monographs documenting the morphologies and stratigraphic occurrences of North and South American mammals. But a decade into his career, he started to publish more synthetic works as well. Simpson collaborated with his wife, Anne Roe, on a classic 1939 book, Quantitative Zoology, that introduced statistical methods and population thinking to evolutionary disciplines that make little sense without them. It was eventually expanded and republished in 1960, with Richard Lewontin added as third author.

Modern Synthesis The late 1930s and early 1940s were pivotal for evolutionary thought as a broader understanding of genetics, biogeography, morphology, and paleontology coalesced into a “modern synthesis” in which gradual, step-by-step morphological evolution is understood to reflect the additive effects of small mutations, while larger-scale speciation and macroevolution are explained in the broader context of geography and environmental change. The conclusion was that small-scale mutation and selection are sufficient to explain what is seen today and in the evolutionary past, and macromutations are not required. The principal architects of the modern synthesis were Theodosius Dobzhansky (Genetics and the Origin of Species [1937]), Julian Huxley (Evolution: The Modern Synthesis [1942]), Ernst Mayr (Systematics and the Origin of Species [1942]), Simpson (Tempo and Mode of Evolution[1944]), and Bernard Rensch (Neuere Probleme der Abstammungslehre: Die Transspezifische Evolution [1947; New problems of phylogenetic systematics: Transspecfic evolution.]).

Simpson’s contribution to the modern synthesis was powerful because it combined his empirical paleontological, quantitative, and systematic experience and brought time on a macroevolutionary and geological scale to the subject. Tempo and Mode of Evolution is widely regarded not only as paleontology’s principal contribution to the modern synthesis, but as a capstone for the synthesis as a whole that integrated all of the relevant disciplines. Simpson developed methods to analyze rates of evolution through time and showed that these were variable. Another innovation was the introduction of the term quantum evolution in an attempt to explain the sudden appearance of new lineages and higher taxonomic groups that were otherwise unexplained. In the preface to a 1984 reissue of Tempo and Mode, Simpson noted that the “punctuation,” or sudden appearance of new species, that is part of current “punctuated equilibrium” theory is essentially a restatement of “quantum evolution” first proposed in Tempo and Mode: “origin of a species or other taxon by exceptionally rapid evolution.”

War Years and After Simpson served a two-year tour of duty in the U.S. Army during World War II from 1942 to 1944. He was a captain and major in the Mediterranean theater in Algeria, Tunisia, and Italy. Simpson was not greatly interested by war and even less enamored of authority. At one point he was attached to General George Patton’s headquarters in Sicily. Simpson wore a short, “pink” beard that displeased Patton, who sent an aide to tell Simpson to remove it. Simpson replied that his commanding officer was General Dwight Eisenhower, who had given him permission to have a beard, and that if Patton wanted it removed, he should take the matter up with Eisenhower (who was also Patton’s commanding officer). Simpson kept the beard.

Following the war Simpson published “Principles of Classification and a Classification of Mammals” (1945). It has served as a standard reference for more than fifty years, and it is still his most-cited work. Simpson’s experience with phylogeny and classification led eventually to his book Principles of Animal Taxonomy(1961). After the war Simpson was appointed chairman of the American Museum’s Department of Geology and Paleontology; simultaneously, he accepted a professorship of vertebrate paleontology at Columbia University.

Simpson was the first president of the Society for the Study of Evolution, founded in 1946, and he helped Glenn L. Jepsen and Mayr organize a pivotal 1947 symposium, Genetics, Paleontology, and Evolution at Princeton, New Jersey. He also set to work at this time revising Tempo and Mode, which was reissued in 1953 as an expanded Major Features of Evolution. Both of these books, classics as they are, remain widely cited.

In 1953 Simpson took his writing in a different direction when he signed a contract to develop a major new university-level biology textbook. This was titled Life: An Introduction to Biology, which appeared in 1957. This first edition was written with Colin S. Pittendrigh and Lewis H. Tiffney, and a revised edition of 1965 was written with William S. Beck. The book reflected the original authors’ strong conviction that there is a unified science of life—a science of biology—which is larger than the then often-separate disciplines of botany and zoology. It is a measure of the authors’ foresight, and to some extent the influence of the new text itself, that botany and zoology departments were subsequently merged in many universities across the United States.

Amazon Expedition Simpson was not always lucky. In 1956 he participated in a joint Brazilian-American Museum expedition to the Rio Alto Juruá at the headwaters of the Amazon. There, while clearing a campsite on 24 August, a tree fell on the fifty-four-year-old Simpson, giving him a concussion, dislocating a shoulder, and shattering a lower leg. It was a week before Simpson could receive adequate medical care, and he was unable to return to work full time at the American Museum of Natural History until 1958. The stress and strain of this long absence led to a series of administrative confrontations, and in 1959 Simpson resigned from the American Museum to accept an Agassiz professorship at Harvard University. Simpson retained his Agassiz professorship at Harvard through 1969, but he suffered a heart attack in 1964 and moved to Tucson and the University of Arizona in 1967 for the sake of his and Roe’s health. Simpson wrote many scientific articles, an autobiography titled Concession to the Improbable (1978), and numerous popular books during his remaining years in Arizona. One of these, Fossils and the History of Life (1983), is a semipopular extension of Major Features of Evolution.

Simpson died in 1984 of pneumonia and complications following a South Pacific cruise. His body was cremated and his ashes scattered in the Arizona desert. A short, introspective novel by Simpson, The Dechronization of Sam Magruder, was discovered and published posthumously. It is interesting for the insight it gives of an exceptional scientist struggling to understand and explain himself.

In retrospect, Simpson is seen as a disciplined and intensely focused scholar, known both for his commitment to observation and for his ability to organize ideas and synthesize interpretations. He was a prolific writer, but a gifted writer, too, able to convey ideas simply and clearly to a wide audience throughout his career. Simpson has been called the greatest paleontologist since Georges Cuvier and the most influential natural historian of the twentieth century. He received many honors, including election to the National Academy of Sciences of the United States in 1941, at the age of thirty-nine. Simpson was awarded the National Medal of Science in 1966 by President Lyndon B. Johnson.


An extensive Simpson bibliography is included in Max K. Hecht, Bobb Schaeffer, Bryan Patterson, et al., “George Gaylord Simpson: His Life and His Works to the Present,” in Evolutionary Biology, vol. 6, edited by Theodosius Dobzhansky, Max K. Hecht, and William C. Steere. New York: Appleton-Century-Crofts, 1972. Simpson’s personal papers and correspondence are archived in the Library of the American Philosophical Society, Philadelphia, available from


A Catalogue of the Mesozoic Mammalia in the Geological Department of the British Museum. London: British Museum (Natural History), 1928.

“American Mesozoic Mammalia.” Memoirs of the Peabody Museum of Natural History, Yale University, New Haven 3 (1929): 1–235.

Attending Marvels: A Patagonian Journal. New York: Macmillan, 1934.

Tempo and Mode in Evolution. New York: Columbia University Press, 1944.

Beginning of the Age of Mammals. New York: American Museum of Natural History, 1948.

With Glenn L. Jepsen and Ernst Mayr, eds. Genetics, Paleontology, and Evolution. Princeton, NJ: Princeton University Press, 1949. The proceedings of the International Symposium on Genetics, Paleontology, and Evolution held in Princeton, New Jersey, in 1947.

The Major Features of Evolution. New York: Columbia University Press, 1953. An expanded version of Simpson’s Tempo and Mode of Evolution.

With Colin S. Pittendrigh and Lewis H. Tiffney. Life: An Introduction to Biology. New York: Harcourt, Brace, 1957.

With Anne Roe and Richard C. Lewontin. Quantitative Zoology. Rev. ed. New York: Harcourt, Brace, 1960.

“The Beginning of the Age of Mammals in South America. Part 2, Systematics: Notoungulata, Concluded (Typotheria, Hegetotheria, Toxodonta, Notoungulata incertae sedis), Astrapotheria, Trigonostylopoidea, Pyrotheria, Xenungulata, Mammalia incertae sedis.” Bulletin of the American Museum of Natural History 137 (1967): 1–259.

Concession to the Improbable: An Unconventional Autobiography. New Haven, CT: Yale University Press, 1978.

Fossils and the History of Life. New York: Scientific American Library, 1983. A semipopular extension of Major Features of Evolution.

The Dechronization of Sam Magruder. New York: St. Martin’s Press, 1996. A posthumously published novel based on Simpson’s self-reflections.


Dobzhansky, Theodosius. Genetics and the Origin of Species. New York: Columbia University Press, 1937.

Gingerich, Philip D. “George Gaylord Simpson: Empirical Theoretician.” In Vertebrates, Phylogeny, and Philosophy, edited by Kathryn M. Flanagan and Jason A. Lillegraven. Laramie: Department of Geology and Geophysics, University of Wyoming, 1986.

Gould, Stephen J. “G. G. Simpson, Paleontology, and the Modern Synthesis.” In The Evolutionary Synthesis: Perspectives on the Unification of Biology, edited by William B. Provine and Ernst Mayr. Cambridge, MA: Harvard University Press, 1980.

Huxley, Julian. Evolution: The Modern Synthesis. London: G. Allen and Unwin, 1942.

LaPorte, Léo F., ed. Simple Curiosity: Letters from George Gaylord Simpson to His Family, 1921–1970. Berkeley: University of California Press, 1987.

———. George Gaylord Simpson: Paleontologist and Evolutionist. New York: Columbia University Press, 2000.

Mayr, Ernst. Systematics and the Origin of Species from the Viewpoint of a Zoologist. New York: Columbia University Press, 1942.

Rensch, Bernard. Neuere Probleme der Abstammungslehre: Die Transspezifische Evolution[New problems of phylogenetic systematics: Transspecfic evolution]. Stuttgart, Germany: Enke, 1947.

Philip D. Gingerich

George Gaylord Simpson

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George Gaylord Simpson

George Gaylord Simpson (1902-1984), an American paleontologist, moved frequently from New York's American Museum of Natural History, where he was curator, to lecture halls and remote fossil fields. His mastery of the fossil record led to significant advances in theoretical evolution and taxonomy.

Paleontology gives rise to the greatest source of empirical knowledge about the history of life. Yet paleontology, which grew and flourished as a descriptive science throughout the 19th and into the early 20th century, contributed little to the theoretical understanding of biology before 1940. George Gaylord Simpson entered this profession in the mid-1920s and demonstrated in the following years that quantitative and deductive methods could lead to accurate and not otherwise accessible conclusions about the history of life.

Education in Colorado and at Yale

George Gaylord Simpson was born in Chicago on June 16, 1902. While he was still very young, his parents, Julia Kinney and Joseph Alexander Simpson, moved to Denver, Colorado, where his father first worked as a railroad claim adjuster and later speculated in irrigation, land development, and mining. George frequently accompanied his father on travels through the mountains, and this led to a lasting fondness for outdoor life and exploration.

Simpson slid easily through grade school, Latin school (ninth grade), and high school in East Denver. Though missing much school for illness, he learned well on his own and graduated in 1918. The following autumn he entered the University of Colorado, where he acquired a particular interest in historical geology, an interest that was sparked and fanned by Arthur Jerrold Tieje. Tieje left Colorado in 1922 and encouraged Simpson to transfer to Yale, which was strong in both geology and zoology. Simpson's senior year was spent at Yale. After graduation in 1923 he immediately entered graduate school and studied with Richard Swan Lull, a leading American paleontologist.

Simpson as Professional Paleontologist

Simpson had begun his professional career even before finishing graduate school. In the summer of 1924 he accompanied William Diller Matthew, paleontologist at the American Museum of Natural History, on a collecting expedition to Texas and New Mexico. Returning to Yale, Simpson continued his study of Mesozoic mammals—the oldest fossilized mammals, of which there was a rare collection in the Peabody Museum at Yale. These mammals became the subject of Simpson's dissertation and led in the year following his graduation to a study of the European Mesozoic mammals at the British Museum. From this work came his first published monograph (1928), although since 1925 he had written somewhat over 30 articles (at his death he had over 700 publications, nearly 50 of which were books).

While in England Simpson received job offers from Yale and from the American Museum of Natural History in New York City. He chose a position with the latter and remained there as curator of vertebrate paleontology until 1959. He served as chairman of the Department of Geology and Paleontology from 1944 to 1958 and held a joint appointment with Columbia University, where he taught vertebrate paleontology from 1945 to 1959. As curator at the museum Simpson received many opportunities to carry out fossil collecting expeditions.

Simpson's early expeditions included travels to Florida, Montana, New Mexico, Argentina (specifically Patagonia), and Venezuela. The Scarritt Expeditions (funded by Horace Scarritt, a wealthy banker) occupied much of the 1930s. Under these Simpson went twice to Patagonia (1930-1931 and 1933-1934). First studying the country's fossil collections in museums at Buenos Aires and La Plata, he later tracked down in Patagonia a field rich with fossil mammals from the early Cenozoic period (the Age of Mammals). At that time little was known of early mammalian history, and the lack of information about South American mammals represented an unusually large gap.

The description and interpretation of Simpson's findings in Patagonia were set forth in his classic work The Beginning of the Age of Mammals in South America (Vol. I, 1948; Vol. II, 1967). Here Simpson told of finding only three groups of mammals in the lower strata (ungulates, edentates, and marsupials). He surmised that South America had been isolated from animal immigration shortly after the origin of mammals in the late Mesozoic (Age of Reptiles) and had remained that way during most of mammalian history (the Cenozoic began approximately 60 million years ago). During this time of isolation, however, South America had received one installment of mammals from another continent. A group of primates and rodents, in a manner which Simpson was unable to explain, colonized South America and flourished toward the middle of the Age of Mammals. Then, in recent time (geologically speaking, in the last few million years) with the origin of a land bridge between North and South America, the southern continent received a flood of invaders from the north and experienced a great increase in mammalian diversity.

Contributions to Evolutionary Thought

Simpson's life changed in two major ways late in the 1930s. First, his marriage failed. It had been a tumultuous one nearly from its beginning in 1923. In 1938 Simpson remarried, and his second wife, a childhood friend, Anne Roe, an academic psychologist, collaborated with him on a textbook, Quantitative Zoology (1939). This book was an outpouring of their mutual belief that most zoologists were inadequately trained in statistics, and it served to give impetus to a shift in zoological methodology. A second change is related. Simpson's expertise in statistics prepared him to take on theoretical problems in biology.

Simpson's first major contribution to theoretical biology was in the area of evolution. Since Darwin, paleontologists had almost exclusively been evolutionists, but, again with little exception, they failed to accept Darwin's mechanism for evolution—natural selection. They commonly believed, as epitomized by H. F. Osborn (a colleague of Simpson at the American Museum during Simpson's early years) that long-term phenomena of evolution (macro evolution), such as speciation or major changes in a line of descent (for example, the shift from three-toed to one-toed horses), required explanations that could only be reached through studies of the fossil record.

Simpson was not a typical paleontologist, however. He had always been adept at mathematics, and Anne Roe had introduced him to the powerful statistical techniques used regularly in her field. Consequently, Simpson was able to recognize the efficacy with which a small group of genetic statisticians were solving problems in evolution. In the 1920s and 1930s R. A. Fisher, J. B. S. Haldane, and Sewall Wright had independently worked out statistical principles by which an advantageous variation could be carried through a population in time and subsequently change the adapted nature of that population. That is, they demonstrated that natural selection could theoretically work. Simpson reconciled these advances in genetics with the fossil record.

Tempo and Mode in Evolution (1942) advanced paleontology in a number of ways. It proposed many means by which evolution might work and demonstrated that hypothesis does have a role in paleontology. It answered the question of whether the fossil record could be reconciled with the new statistical approach that geneticists had applied to natural selection and laid the groundwork for a union of micro and macro evolution in a single principle. It also showed that the fossil record can be described and interpreted quantitatively. Broadly, it formed part of the greater synthesis which united all the various biological subdisciplines in a common understanding of evolution.

Simpson also became an expert on the classification of mammals. Shortly after being hired by the American Museum, he began compiling a catalogue to facilitate storage and retrieval of the museum's extensive collection of mammals. He collected all the contemporary studies in mammalian taxonomy and produced a systematic classification of the mammals organized down to the level of family. This was published in 1931. By 1942 Simpson had written a greatly expanded version. This book, published in 1945, was praised as the first attempt to organize and set forth explicitly the principles of an evolutionary taxonomy.

The Halcyon Period

Simpson called the period 1944 to 1956 the halcyon period of his life. He continued studies in evolution, participated in the founding of the Society for the Study of Evolution, and wrote two books on this subject. The Meaning of Evolution (1949) was written for a wide audience and became Simpson's most popular book. Major Features of Evolution (1953) was an extensively revised version of Tempo and Mode in Evolution. During this period Simpson also wrote a general book on paleontology, Life of the Past (1953), and continued his research on fossil mammals.

Research in 1954 took him to Brazil under invitation from the Brazilian National Research Council. There he lectured, consulted Brazilian scientists, and studied mastodons in museums and in the field.

A second expedition to Brazil, in 1955, ended with a severe accident, which forced Simpson to be immediately transported back to New York City and left him crippled for two years. During his recuperation he published a textbook on general biology, Life (1957), with C. S. Pittendrigh and L. H. Tiffany. The text was used extensively and employed a novel approach to biology, presenting evolution as the central principle while ignoring the traditional dichotomy between plants and animals.

As a consequence of his lingering disability, Simpson was removed from the chairmanship of the Department of Geology and Paleontology at the American Museum. Subsequent developments led to his resignation as curator of vertebrate paleontology at the museum and as professor at Columbia University in 1959. Shortly thereafter Simpson became the Alexander Agassiz Professor at the Museum of Comparative Zoology (aligned with Harvard University).

Simpson carried on his research from Cambridge for the following eight years. During this time he published his favorite book, This View of Life (1964), which was a collection of previous, shorter works (Simpson preferred to lecture from a written text rather than from notes). Simpson also travelled extensively during this period. The height of these travels was perhaps an African expedition with Louis and Mary Leakey when they made their famous discovery of a 14 million year old human ancestor at the Olduvai Gorge in Kenya.

The Later Years

In 1967 the failing health of both Simpson and his wife forced them to move to Tucson, Arizona. Simpson remained employed half-time by the Museum of Comparative Zoology and continued his research under its auspices until 1970. In addition, he served as part-time professor at the University of Arizona, where he remained until full retirement in 1982.

During the late 1960s and early 1970s Simpson and Anne Roe continued to travel extensively, despite failing health. In Patagonia in 1933 Simpson had made an extensive collection of fossil penguins. He worked on this collection only sporadically, but after his partial retirement in 1970 he found great pleasure in studying them. This study took him and Anne to museums in London and Stockholm; on field expeditions to South Africa, Australia, and New Zealand; and on three cruises to Antarctica. The result was the book Penguins: Past and Present, Here and There (1976).

Throughout his life, Simpson worked tirelessly and with great enthusiasm. Complete retirement in 1982, when he left his professorship at the University of Arizona, was merely a nominal change-two books published after retirement—Fossils and the History of Life (1983) and Discoverers of the Lost World (1984)—attest to his tenacious desire to work, ending only with his death late in 1984.

Further Reading

There is not much secondary literature on Simpson's life and work. Further details can be found in his autobiography, Concession to the Improbable (1978). Stephen Jay Gould has written a short article on Simpson's role in the union of paleontology and theoretical evolution in The Evolutionary Synthesis, edited by Ernst Mayr and William B. Provine (1980). In the same work Mayr has written a short biography of Simpson that focusses on his scientific achievements. On the other hand, a wealth of primary works is readily available, and one can find a comprehensive list of Simpson's publications up to 1971 in Hecht, et. al., "George Gaylord Simpson: His Life and Works to the Present," Evolutionary Biology 6 (1972). Simpson's book Attending Marvels (1934) is a charming account of his travels in Patagonia. □

George Gaylord Simpson

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George Gaylord Simpson


American Paleontologist

A pioneer in the application of statistical methods to paleontology, George Simpson added immensely to scientific knowledge concerning prehistoric life. In the course of a long career that took him to varied destinations around the globe, he analyzed fossil remains, and from these derived information about migratory patterns, evolutionary histories, and other facts of the distant past. He was also a prolific writer who produced several important texts.

The youngest of three children, Simpson was born in Chicago on June 16, 1902, to Joseph and Helen Kinney Simpson. When Simpson was a baby, his father, a lawyer, took a job as a railroad claims adjuster in Denver, Colorado; later he became a land speculator. Simpson credited his father for taking him on many hikes and camping trips, which engendered in him a love of the outdoors that would aid him throughout his career.

A brilliant student, Simpson finished high school several years early, and in 1918 entered the University of Colorado. Later, a professor convinced him to make the transition to Yale, from which he graduated with a bachelor's degree in 1923. Also in 1923, he married Lydia Pedroja, with whom he had four daughters.

In 1926 Simpson earned his doctorate at Yale. His dissertation concerned fossils in the Peabody Museum collection dating from the Mesozoic era, a period that marked the first appearance of mammals. Later, he received a fellowship to study Mesozoic mammals at the British Museum in London. By 1927 he was back in the United States, where he took a position as assistant curator at the American Museum of Natural History in New York.

Simpson would remain at the museum for more than three decades, during which time he conducted his most important research. He eventually became curator of fossil mammals and birds, as well as chairman of the department of geology and paleontology, and, from 1945 to 1959, he taught at Columbia University.

In April 1938 Simpson and Lydia divorced, and a month later he remarried to Anne Roe, a psychologist with whom he had been friends since childhood. With Roe's knowledge of statistics and Simpson's expertise in paleontology and zoology, the two collaborated on a number of projects, including the textbook Quantitative Zoology, published in 1939. Simpson followed this in 1944 with Tempo and Mode in Evolution, his most important work, in which he demonstrated that fossil findings could be quantified. Furthermore, he showed that the fossil record could be shown to align with emerging knowledge at the nexus of population genetics and natural history.

From 1942 to 1944 Simpson served in World War II as an army officer, with tours of duty in North Africa and Italy. After he returned to the United States, he conducted extensive fieldwork in New Mexico and Colorado, searching for mammal fossils from the Eocene (54 million years ago) and Paleocene (65 million years ago) eras. Most prominent among his finds were 15 inch (38.1 cm) high creatures he named Dawn Horses. In 1949 he published The Meaning of Evolution, a text that presented the complexities of evolutionary theory in easy-to-understand language.

Misfortune struck Simpson while conducting fieldwork in Brazil in 1956. A tree felled by an assistant clearing a campsite fell on him, leaving him with a concussion and such severe injuries that he could not walk for two years. He was forced to resign his position at the American Museum, but in the quarter-century that followed he traveled and wrote extensively. Among his most significant expeditions was a 1961 trip to Kenya with Louis Leakey (1903-1972), during which Leakey discovered a highly significant skull fragment. The fragment was subsequently linked with Ramapithecus, believed to have been a human ancestor from 14 million years ago.

In 1967 Simpson and his wife move to Tucson, Arizona, where he took a position with the University of Arizona. The couple also established the Simroe Foundation, a nonprofit agency intended to disseminate the knowledge they had gathered. He received a number of awards and belonged to several professional associations. In 1982 Simpson retired, and, on October 6, 1984, he died of pneumonia at a hospital in Tucson.


Simpson, George Gaylord

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Simpson, George Gaylord

American Paleontologist and Biologist 1902-1984

George Gaylord Simpson was born to middle-class parents in Chicago, Illinois, on June 16, 1902. The family soon moved to Colorado, where he became fascinated by the dramatic geology and vertebrate fossils of the West. Graduate work at Yale University culminated in a Ph.D. in Geology in 1926 with a thesis on Mesozoic mammals. Simpson married psychologist Anne Roe and later collaborated with her on several books and conferences about behavior and evolution.

In 1927 Simpson began his thirty-two-year association with the American Museum of Natural History, of which he became curator in 1942. During those years he led expeditions to Mongolia, Patagonia, and Montana and taught at Columbia University. His work in organizing all the known fossil vertebrates of the Mesozoic, Paleocene, and Eocene was summarized in a series of textbooks including: Tempo and Mode of Evolution (1944), The Meaning of Evolution (1949), and The Major Features of Evolution (1952). His most significant achievement may be the application of population genetics to the analysis of the migration of extinct mammals between continents.

From 1959 to 1970 Simpson was professor of vertebrate paleontology at the Museum of Comparative Zoology at Harvard University. In 1967, at the age of sixty-five, he moved to Tucson to become professor of geosciences at the University of Arizona.

Simpson's lifelong enthusiasm for and contributions to his chosen field were recognized by numerous honorary degrees and medals worldwide. He was elected to the National Academy of Sciences in 1941 and the National Academy of Arts and Sciences in 1948. He was cofounder and first president of both the Society of Vertebrate Paleontologists and the Society for the Study of Evolution. George Gaylord Simpson died October 6, 1984.

Nancy Weaver


Greene, Jay, ed. Modern Scientists and Engineers, vol. 3. New York: McGraw-Hill, 1980.

Porter, Ray, ed. The Biographical Dictionary of Scientists. New York: Oxford University Press, 1994.

Simpson, George Gaylord. Attending Marvels: A Patagonian Journal. New York: Time-Life Books, 1965.

Simpson, George Gaylord

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Simpson, George Gaylord (1902–84) An American palaeontologist, specializing in mammalian evolution, who also studied mammal migrations. He obtained his Ph.D. from Yale University in 1926, for a thesis on Mesozoic mammals, and then joined the staff of the American Museum of Natural History, in New York City, becoming curator in 1942. In 1945 he moved, as a professor, to Columbia University. From 1959 to 1970 he was Alexander Agassiz Professor of Vertebrate Palaeontology at the Museum of Comparative Zoology at Harvard University, and in 1967 was appointed professor of geosciences at the University of Arizona. His studies of fossil mammals, especially those of Madagascar, led him initially to oppose the theory of continental drift. Simpson proposed that the dispersion of species occurred along sweepstakes dispersal routes.

Simpson, George Gaylord

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Simpson, George Gaylord (1902–84) An American palaeontologist, specializing in mammalian evolution, who also studied mammal migrations. He obtained his Ph.D. from Yale University in 1926, for a thesis on Mesozoic mammals, and then joined the staff of the American Museum of Natural History, in New York City, becoming curator in 1942. In 1945 he moved, as a professor, to Columbia University. From 1959 to 1970 he was Alexander Agassiz Professor of Vertebrate Palaeontology at the Museum of Comparative Zoology at Harvard University, and in 1967 was appointed Professor of Geosciences at the University of Arizona.

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