NICOLAUS STENO, SPONTANEOUS GENERATION, AND THE GREAT FOSSIL DEBATE

During the Renaissance and Early Modern period a popular explanation for fossil marine shells found in mountains and regions distant from the sea was the Aristotelean doctrine of spontaneous generation. In his History of Animals Aristotle wrote that mollusks and other "non-copulative" organisms reproduced exclusively by spontaneous generation and would necessarily arise in abundance wherever conditions were appropriate. Salty desert soils and limey mountain bedrock, if infiltrated by meteoric water, could mimic the conditions in marine sediments and therefore give rise to populations of mollusks, which would then die and petrify in situ, creating fossil beds. The Prodromus on Solids (1669) by Nicolaus Steno (1638-1686) is generally acknowledged to be the foundational text of paleontology with its decisive critique of inorganic theories of fossil growth in situ, favored by many prominent scientists of the day. But the Prodromus alludes only briefly to spontaneous generation. There is evidence, however, that contemporary research and arguments against spontaneous generation helped frame Steno's thinking about the origin of fossils. During the period of Steno's initial studies of fossils he collaborated closely with Francesco Redi, who was then engaged in his famous experiments refuting the spontaneous generation of insects. Steno was also in close contact with the microscopicists Jan Swammerdam and Marcello Malpighi, who were studying the reproductive biology of various invertebrates and plants. Coupled with Steno's own anatomical work on reproductive biology, this likely led Steno to rule out spontaneous generation at the outset of his study, allowing him to focus on distinguishing organic from inorganic growths. Interestingly, it was in the context of the spontaneous generation debates that Malpighi defended Steno's theories on fossils and strata, and it was likely through him and his students that these ideas were passed down to later generations of Italian geologists, culminating with Giovanni Arduino, who 1760 laid the foundations for our present geologic timescale.