Martin Rudwick's latest work, Worlds before Adam (hereafter WBA), is a mighty sequel to his massive volume Bursting the Limits of Time (hereafter BLT; Chicago: University of Chicago Press, 2005; reviewed in RNCSE 2006 Nov/Dec; 26 : 35–6). Together they constitute a magnum opus from one of the world's foremost historians of geology and paleontology. Like its predecessor volume, WBA is a weighty book that details the efforts of 19th-century geologists to reconstruct an immensely long and eventful earth history, or "geohistory," as Rudwick puts it in his title.This book begins where the previous one leaves off, in the years following the end of the Napoleonic era (circa 1817), when the French comparative anatomist Georges Cuvier still wielded considerable influence in geology, and ends in the early 1840s, when Louis Agassiz's glacial theory "forced geologists to recognize the contingent character of geohistory as a whole" (p 7). Rudwick divides his book into thirty-six well-written and lavishly illustrated chapters arranged chronologically and grouped into four parts. Part I begins in Paris with Cuvier, vertebrate paleontology, and earth's natural "revolutions," then moves to Great Britain, where important contributions to stratigraphy and paleontology were often interpreted in Biblical terms, and ends with a lengthy discussion of the debates about the adequacy of "actual" causes in explaining geological events of the distant past.Could small, observable changes in elevation during earthquakes, for example, account for crustal movements on a more massive, mountainous scale? Part II deals with the late 1820s and earliest 1830s, when French and English geologists such as Alexandre Brongniart, Louis-Constant Prevost, and William Buckland grappled with questions of a cooling earth, fossil faunas, glaciers, extinction and much more.
Part II ends with Chapter 17, "The specter of transmutation (1825–1829)," which deals briefly (in twelve pages) with the subject of evolution, which is only "loosely linked" (p 237) to the central issues of WBA.As Rudwick argues, Cuvier had already established the reality of extinction by the 1820s, when almost all naturalists agreed that many of the strange fossil remains turning up in all quarters of the globe represented species long gone.Whether it was brought about by gradual, local changes of climate, or through massive catastrophes, the fact of extinction was no longer a question. Explanations for the origins of new species remained steeped in controversy, however, especially as evidence accumulated for the successive appearance of new organisms in the fossil record.
Jean-Baptiste de Lamarck had all but ignored the fossil evidence in his general theory of transmutation published in 1809. Fossils were Cuvier's bailiwick, and he abhorred transmutation. In 1825, however, Cuvier's colleague Etienne Geoffroy Saint-Hillaire published a paper in which he argued that living gavials might be the direct descendants of the fossil crocodiles found in the Secondary formations of Normandy, and he tied his argument explicitly to Lamarckian transmutationism. Geoffroy used a widely approved actualistic approach to make his case, arguing that analogous "monstrosities," which could be directly observed in the present world, represented more significant morphological variability than that which was required to explain the cumulative transformation of vertebrate animals over the course of geohistory.But he badly mishandled the fossil record, suggesting that a "progressive series" of fossil vertebrates could be traced from "the ichthyosaur ... and pterodactyl, then passed by way of the ... mosasaur and the Caen crocodile to the American megatherium ... and ended with the Parisian palaeotherium and anoplotherium" (p 242). Geoffroy's hopelessly confused series did not win converts. Moreover, according to Cuvier, there was as yet a conspicuous absence of intermediate forms between fossil and living species.
The important point, though, is that theories of transmutation were still kicking around, at least in France, and they played a role in the continuing debate over how paleontologists were to interpret the history of life. Indeed, Lamarck's Zoological Philosophy inspired a book-length repudiation by the English barrister and geologist Charles Lyell, who felt compelled to "defend his own species from the indignity of being assigned a merely animal origin" (p 246).
Ultimately, the theoretical background did not matter. What mattered most to the practicing geologist of 1830 was to determine when species went extinct, when new ones appeared, and whether they did so suddenly, gradually, in bunches, or one at a time. In short, geologists could reconstruct the history of life on earth without the necessity of appealing to any causal explanation. Debates about the transmutation of species, Rudwick argues, developed "in parallel with the reconstruction of geohistory, with only a loose linkage between them" (p 249).This explains the relatively marginal position that evolution occupies in his book.
Part III is devoted largely to Lyell and his contemporaries and critics, as they debated the merits of his influential Principles of Geology and its uniformitarian approach in the 1830s. Finally, Part IV takes the story of geologists and geohistory into the early 1840s, by which time reconstructing geological events and deducing their causal explanations had become standard practice.
In spite of their intimidating mass, WBA and BLT together are not a comprehensive history of geology, nor are they intended to be. Whole subfields of geology, including mineralogy, petrology, and structural and economic geology, are largely ignored in favor of the more obviously historical fields of stratigraphy and paleontology. This makes perfect sense in light of Rudwick's goal of chronicling the ever-expanding geohistorical approach of earth scientists in the early 19th century. Rudwick claims, with excessive modesty, that he hopes his work will serve as a starting point for further research. But with so grand a beginning, the prospect of writing a worthy contribution in history of geology seems daunting indeed. WBA is a work of such excellence as to recommend it to anybody.