Meghan Page (Loyola University, Maryland)
Models of “good science” often appeal to successful predictions and observable empirical results. This poses a problem for historical sciences, such as archaeology, evolutionary biology, and geology, that investigate historical events. It is difficult to replicate evolutionary stories in a laboratory, and the past that is no longer accessible for direct observation (e.g. we can’t watch dinosaurs eat to determine their palate.) These structural differences between historical science and experimental science have led to doubts whether claims about the past, even those made by experts, can be successfully verified by science.
Carol Cleland offers a powerful defense of historical science by appealing to what David Lewis describes as “the asymmetry of overdetermination.” The asymmetry of overdetermination is a causal asymmetry---an event is usually underdetermined by any particular cause (e.g. tossing a baseball towards a window is not a guarantee that the window will break) but causes are epistemically overdetermined by their effects (if the baseball does break the window, it will leave a host of traces to prove that it did.) The widespread traces left by events on the world act as a breadcrumb trail---by uncovering enough of these traces, scientists navigate a path to an explanation through the search for a common cause.
According to Cleland, both models of science, experimental and historical, are justified by the asymmetry of overdetermination. Because causes do not uniquely determine their effects, experimental scientists repeatedly test their hypotheses to isolate relationships between variables; scientists must verify they are tracking regularities and not accidents, and to do this they must isolate individual causal relationships from the complex web of total causes that converge at any particular event. In contrast, historical scientists trace a specific path from effect to cause. Given that any actual event leaves a great number of effects, scientists can rely on these traces to distinguish between competing causal explanations.
While Cleland’s picture is compelling and accommodates many historical research programs, it fails to account for the specific role of historical science in making claims about the future. This is contrary to practice, considering, for example, that some of the best evidence we have concerning the relationship between CO2 emissions and abrupt global climate change comes from historical sciences such as glaciology and paleoclimatology.
In this poster, I present a case-study concerning the introduction and verification of Walter C. Broecker’s hypothesis that there are alternating modes of operation in the meridional overturning circulation. Broecker’s historical work interpreting ice core data led him to hypothesize that there are differing modes of circulation in oceanic deep currents that, if switched, can lead to abrupt changes in climate. A number of predictions that follow from Broecker’s hypothesis (some historical, some not) have have proven accurate, offering support for his claim. I use this case as a reductio against Cleland’s view. If Cleland is right, historical science is only justified in making claims about the past. But historical science often offers successful predictions about both regularities and future events. Therefore, Cleland’s view is problematic.
