Selected Letters Between Steve Gould, Tom Schopf, and Dave Raup about the “MBL Model” This packet contains letters written between 1972 and 1981 by members of the group that authored the so-‐called “MBL model” papers described in the Gina Kolata article in Science. I apologize about the scan quality on some of them, but collectively they give a nice insight into the background discussions about the model and its potential implications, as well as a view of the personalities involved. For a more detailed history of the MBL model see either the Sepkoski or Huss papers in the Further Readings section for this topic, but here is a brief summary of the context: In 1971, Tom Schopf, a young invertebrate paleontologist at the University of Chicago, organized a symposium at the Geological Society of America meeting on “Models in Paleobiology.” Schopf, like his friends Steve Gould (recently appointed at Harvard) and Dave Raup (then at the University of Rochester), wanted to inject what Schopf called “greater analytical rigor” into the practice of paleontology, which they viewed as too descriptive and conservative. Schopf asked Gould to give a talk on “Models of Speciation,” and with co-‐author Niles Eldredge Gould presented the first version of what would be the original paper on “Punctuated Equilibria” (published in the symposium volume in 1972). Immediately after the symposium, Schopf decided to take advantage of the momentum he had created by organizing a weekend brainstorming session at Woods Hole, where he had an affiliated research position, to consider further applications of models to paleontology. He invited Gould, Raup, and the young theoretical ecologist (and E.O. Wilson student) Dan Simberloff, and the group spent several days trying to figure out how to derive quantitative models from empirical data sets like the Treatise on Invertebrate Paleontology. Simberloff had been invited because of his experience with quantitative ecological models, and Raup was the computer guru of the group, having written a series of papers in the late 1960s in which he used computers to simulate the morphology of coiled shells. However, after two days with little success, the group concluded that the fossil data they were working with was too fragmentary and incomplete to work with. In desperation, Raup came up with the idea of creating a computer simulation in which evolutionary phylogenies were generated and randomly subjected to probabilities of branching or termination in order to see what evolution might look like in a world where the success of lineages was not determined by selection. This was explicitly considered a thought experiment, since the null hypothesis was that we do live in a Darwinian world governed by natural selection. After the first meeting, Raup wrote a very simple program, and the initial paper (published in 1973) described the results. Those results are discussed in the Kolata article, but very briefly, the authors were impressed by the fact that the simulated lineages looked surprisingly similar to actual evolutionary phylogenies. This suggested that existing patterns of evolution could have been produced by stochastic (random) factors alone, but the authors did not argue that they actually were. After this initial meeting and paper, Schopf convened the group again—this time including Jack Sepkoski (my dad), who was a young graduate student working with Gould—to plan several follow-‐up papers. The results were a paper written by Gould and Raup in which the simulation was extended to include the evolution of morphological traits, and the group collaboration concluded with a paper broadly comparing results of the simulation runs with data from the actual fossil record. These papers can be found in the Recommended Readings section on the website. During this time, members of the group developed differing interpretations of their results. Initially, Schopf, Gould, and Raup were highly impressed by the potential for the model to suggest that many evolutionary processes might actually be stochastic. Schopf, in particular, developed a vision of a “stochastic paleontology” in which species or higher taxa could be treated mathematically like molecules interacting randomly in a volume of gas. As time went on, however, Raup and Gould became less sure about this metaphor. The letters give a flavor of the debates that went on between the three. Ultimately, a paper by Steve Stanley and others showed that the original MBL model suffered from scaling problems, and was not a good simulation of actual evolutionary history. This led Raup and Gould (the latter more reluctantly) to withdraw most of their enthusiasm for the model. Schopf, however, stuck to his guns until his untimely death in 1984, and continued to promote his vision of a stochastic view of life (see Further Readings). Although the MBL model did not revolutionize paleontology as its authors originally hoped, it had a significant influence on the development of what many paleontologists now call “paleobiology,” and in particular on the evolving views of Gould. As I’ve argued elsewhere, it may have been the initial basis for Gould’s understanding of the role of contingency in the history of life, and it sparked continuing debates about the interplay of chance and determinism in evolution (Dan McShea and Robert Brandon’s 2010 book Biology’s First Law is essentially a philosophical reconsideration of the MBL experiment). The MBL model also signaled the importance of computer modeling for paleontology, and inspired Raup and Sepkoski to develop approaches to model and analyze fossil data to explore patterns of diversification and evolution in the history of life that have influenced the entire field. Gould drew on this further work in his theoretical explorations of macroevolution during the 1980s and beyond, as seen for example in his paper “The Promise of Paleobiology as a Nomothetic, Evolutionary Discipline.” All of the papers below are available on the seminar website. Recommended additional reading: -‐ Raup, Schopf, and Gould, "Stochastic Models of Phylogeny and the Evolution of Diversity" [The original MBL Model paper, published in 1973] -‐ Raup and Gould, "Stochastic Simulation and the Evolution of Diversity -‐ Towards a Nomothetic Paleontology" [A later paper in the MBL series, perhaps the most important, showing how a stochastic model could influence the evolution of morphological diversity] -‐ Gould, "The Promise of Paleobiology as a Nomothetic, Evolutionary Discipline" [One of two manifestos published by Gould in the same issue of the journal Paleobiology in 1982, this paper brings together Gould's vision of a "nomothetic" paleontology with his emerging hierarchical thinking. A contentious classic in the field.] Optional for further exploration: -‐ Sepkoski, "“Towards a Nomothetic Paleontology”: The MBL Model and Stochastic Paleontology" [The chapter from my book that tells the story of the MBL model in considerable detail, with attention to the internal divisions and arguments within the group of authors] -‐ Huss, "The Shape of Evolution: The MBL Model and Clade Shape" [John Huss' excellent short summary of historical and philosophical issues surrounding the MBL Model] -‐ Gould, "Generality and Uniqueness in the History of Life" [Gould's summary of the MBL papers for an audience of biologists-‐-‐fairly technical] -‐ Gould et al., "The Shape of Evolution: A Comparison of Real and Random Clades" [The last MBL collaborative paper, in which the authors test the model against real data. This paper led to the fairly devastating critique by Stanley et al.] -‐ Stanley et al., "Natural Clades Differ from "Random" Clades: Simulations and Analyses" [The Stanley et al. critique of the MBL Model] -‐ Schopf, "Evolving Paleontological Views on Deterministic versus Stochastic Approaches" [Schopf's broad methodological defense of stochastic paleobiology]