Miranda Paton Cornell University My dissertation, “Vertebrate Paleontology and the Evolutionary Synthesis, 1894-1944,” describes the reorganization of modern evolutionary biology during the 1930s and 1940s from the perspective of a discipline that purportedly contributed very little. During the Evolutionary Synthesis, George Gaylord Simpson (1902-1984) published Tempo and Mode in Evolution, a smart but rather tame demonstration that Sewall Wright’s genetic model of evolution could be extrapolated to fossil taxa and therefore explain the unobservably slow natural process. A useful synthesis of biology, then, entailed more work on the kinds of questions organized by students of theoretical population genetics. Throughout a career spanning the complicated half-century before the Evolutionary Synthesis, Henry Fairfield Osborn (1857-1935) tried to organize a very different kind of unifying research program for biology. Osborn appreciated the deep methodological divides that separate paleontology from the kinds of demographic and laboratory-based work that can experimentally study the relationship between random genetic mutation and natural selection, if only in the shortest stretches of time. Osborn believed that inheritance was not random at all, but poorly understood and thought that patterns in the fossil record might shed light on this central problem in evolutionary biology. Osborn failed to convince Darwinians that they were making a philosophical mistake by choosing an admittedly incomplete theory for the virtues of its supporting methodological framework rather than shaping a science to fit the data and questions gathered from disciplines that were diverse but equally empirical in their own terms. Had Osborn’s objections found a more sympathetic audience, things might have gone differently. This history compares Osborn’s and Simpson’s attempts to defend the value of paleontologists’ theoretical claims and specialized methods to the shifting interdisciplinary community of evolutionary biologists outside of paleontology that largely controlled the field’s overarching research program. Having extracted all the information I could from Osborn’s and Simpson’s published papers, I still had questions about how and why they defended their respective views of evolution to contemporaries. My month in Philadelphia area archives and Princeton University collections helped answer three specific questions that remained. Why did Osborn dissent from Darwinian explanations for evolution and assert that paleontology could add something to experimental studies of inheritance and evolution? Edward Drinker Cope and Othniel Charles Marsh dominated American vertebrate paleontology between the 1870s and late-1890s, the first third of Osborn’s career. To enter the field meant choosing a side and Osborn allied himself with Cope. Osborn admired Cope’s attempt to make vertebrate paleontology do more than confirm Descent With Modification and the general Darwinian claim that organisms change along with their surrounding environment. Cope also identified a pattern in the fossil record—instances parallel, linear evolution among mammals separated by vast stretches of ancestry, time and space—that seemed poorly explained by the local process of natural selection. An expanding data set, the increasingly baroque and untenable neo-Lamarckian explanations for parallelisms Cope defended up to his death in 1897, plus the recognition that any progress in evolutionary theory would come from progress toward a theory of inheritance together shaped Osborn’s research agenda. Archival collections in Princeton University’s Seeley G. Mudd and Firestone Libraries supplied background information related to Osborn’s entry into a branch of biology that had an uneasy relationship with evolutionary theory. Letters between Osborn and his family members, as well as between Osborn and his Princeton classmates show that even as a young man, Osborn planned to make a substantial contribution to science. I also wanted to gather as much information as I could about the development of Cope’s ideas about the relationship between different kinds of inherited variations and evolutionary patterns. Cope spent his career in Philadelphia and Haddonfield, New Jersey, but only the very few letters preserved within collections of other naturalists’ papers remain. I found small but useful caches of Cope’s letters in the Wagner Free Institute and the Ewell Sale Stewart Library at the Academy of Natural Sciences in Philadelphia. A set of letters between Cope and the American invertebrate paleontologist (and fellow neo-Lamarckian), Alpheus Hyatt in Princeton’s Hyatt and (Alfred Marshall) Mayer Collection were especially useful, shedding some light on why Cope thought that the production of new species and new genera required separate causal explanations. How did other evolutionists respond to Osborn’s (changing) theoretical claims during the 20th century? Osborn modified his explanation for linear evolution three times over the course of his career, in each instance promoting a theory that accommodated current ideas about inheritance and the production of morphological adaptations. Osborn exchanged his faith in the inheritance of acquired characteristics in 1889 for his own version of Organic Selection proposed in 1896 along with similar ideas promoted by James Mark Baldwin and Conwy Lloyd Morgan as a synthesis between Evolution By Natural Selection and the responsive inheritance at the center of neo-Lamarckian theory. Osborn quickly abandoned Organic Selection and developed Orthogenesis—the claim that genetic mutations (perhaps comparable to the Mendelian mutations considered by experimentalists) occur in long-term patterns visible only in the long spans of time represented by fossil phylogenies. I scoured collections at the American Philosophical Society (particularly the correspondence of William Bateson, Charles Davenport and a collection of letters between Hans Driesch and Thomas Hunt Morgan) to find correspondence with Osborn or about him. Edwin Grant Conklin’s letters at Princeton University were also particularly useful in this part of my research. Private correspondence revealed what published work could not: There was no reason to ignore Osborn, however unpopular his views of evolution. Most scientists gave Osborn the rather stiff respect he demanded but they also valued the famous paleontologist (especially in the 1910s and 1920s) as an able and ready defender evolution as a natural process amenable to rigorous scientific investigation. Even in private discussions of evolutionary research, Osborn’s contemporaries gave Orthogenesis a wide berth and largely ignored the problem of fitting evolutionary theories to the fossil record. If the rediscovery of Mendel’s particulate theory of inheritance effectively requires biologists to study the relationship between inherited variation and selection within closed populations, why consider any view of evolution based the study of change at very high taxonomic levels after 1900? From a modern perspective, one that distinguishes competition between individual organisms from competition between species, there seems to be an obvious explanation for the silence between early geneticists and paleontologists: They study different evolutionary phenomena because they work at different taxonomic levels. In their published papers, however, neither Osborn nor his laboratory-based colleagues seem to have appreciated the problem. In fact, Sewall Wright and J. B. S. Haldane supplied alternatives to Orthogenesis in the early 1930s after Osborn published his substantial monograph on the linear evolution of the extinct Titanothere group in 1929. I made a thorough search for evidence that pre-Synthesis evolutionists understood the difference between what biologists now call micro- and macroevolution. I was genuinely surprised to find no discussion of the problem in all of the correspondence between Osborn and his contemporaries, or even between Simpson and his far more sophisticated cohort. (Simpson published a 1951 paper on the definition of “paleospecies” as a taxon that ought to correlate to the systematist’s living species; I found a single 1949 letter from invertebrate paleontologist Norm Newell that obliquely addressed the problem of identifying species in paleontology.) I also read Sewall Wright’s correspondence with Osborn (one 1931 letter) and the more extensive set of letters with statistician R. A. Fisher with the same question about hierarchical evolution in mind. By 1932 neither geneticist seemed to have worried about the relationship between Mendelian populations and wild species, or between the population-level processes they could model in mathematical terms and a natural process, which might crucially involve species-level selection. More correspondence between George Gaylord Simpson and his colleagues before and after the Synthesis in the APS Library helped me understand why Simpson thought that he could (or ought to) defend a comparison between purely theoretical genetic populations and paleospecies. This focused month of work in archival collections late in my dissertation substantially improved my project. I am grateful to members of the PACHS consortium—its director Babak Ashrafi and Bonnie T. Clause and research fellows (especially Teddy Varno) who asked insightful questions about my project and made valuable suggestions for my research. I also wish to acknowledge the particularly generous and skilled archivists who knew their collections well, took interest in my project and led me to sets of letters I might not have discovered on my own. I thank Val Lutz and Charlie Greifenstein at the American Philosophical Society, Eileen Mathias at the Academy of Natural Sciences and especially John Delooper at Princeton’s Mudd Library.