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.

Associated Organizations

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.