Abstract
Abstract. There have been repeated calls for a Darwinian approach to hydrologic science, or for a synthesis of Darwinian and Newtonian approaches, to deepen understanding of the hydrologic system in the larger landscape context, and so develop a better basis for predictions now and in an uncertain future. But what exactly makes a Darwinian approach to hydrology "Darwinian"? While there have now been a number of discussions of Darwinian approaches, many referencing Harte (2002), the term is potentially a source of confusion because its connections to Darwin remain allusive rather than explicit. Here we suggest that the Darwinian approach to hydrology follows the example of Charles Darwin by focusing attention on the patterns of variation in populations and seeking hypotheses that explain these patterns in terms of the mechanisms and conditions that determine their historical development. These hypotheses do not simply catalog patterns or predict them statistically – they connect the present structure with processes operating in the past. Nor are they explanations presented without independent evidence or critical analysis – Darwin's hypotheses about the mechanisms underlying present-day variation could be independently tested and validated. With a Darwinian framework in mind, it is easy to see that a great deal of hydrologic research has already been done that contributes to a Darwinian hydrology – whether deliberately or not. We discuss some practical and philosophical issues with this approach to hydrologic science: how are explanatory hypotheses generated? What constitutes a good hypothesis? How are hypotheses tested? "Historical" sciences – including paleohydrology – have long grappled with these questions, as must a Darwinian hydrologic science. We can draw on Darwin's own example for some answers, though there are ongoing debates about the philosophical nature of his methods and reasoning. Darwin used a range of methods of historical reasoning to develop explanatory hypotheses: extrapolating mechanisms, space for time substitution, and looking for signatures of history. Some of these are already in use, while others are not and could be used to develop new insights. He sought explanatory hypotheses that intelligibly unified disparate facts, were testable against evidence, and had fertile implications for further research. He provided evidence to support his hypotheses by deducing corollary conditions ("if explanation A is true, then B will also be true") and comparing these to observations. While a synthesis of the Darwinian and Newtonian approaches remains a goal, the Darwinian approach to hydrologic science has significant value of its own. The Darwinian hydrology that has been conducted already has not been coordinated or linked into a general body of theory and knowledge, but the time is coming when this will be possible.
Highlights
We discuss some practical and philosophical issues with this approach to hydrologic science: how are explanatory hypotheses generated? What constitutes a good hypothesis? How are hypotheses tested? “Historical” sciences – including paleohydrology – have long grappled with these questions, as must a Darwinian hydrologic science
Wagener et al (2013) argued for the need for a “Darwinian” approach to prediction in ungauged basins, and discuss many of the concepts and approaches that have been given the term “Darwinian”. Many of these visions cite Harte (2002) as an inspiration, who suggested that Earth systems science needs new approaches to dealing with the formidable difficulties of global change. He suggested that new approaches ought to find a synthesis of the disciplinary worldviews that dominate within physics and ecology
We propose that the Darwinian approach to hydrology is distinct from the Newtonian in the type of question it seeks to answer about the hydrologic cycle
Summary
To a number of evolutionary scientists, notably Ghiselin (1969) and Gould (1983), a key contribution of Darwin’s work was his masterful way of doing “historical” sciences that connected observations of current forms with mechanisms and processes operating over time (much of what follows is drawn from these references and from “On the Origin of Species” (Darwin, 1859), “The Formation of Vegetable Mould through the Action of Worms” (Darwin, 1881), and “The Structure and Distribution of Coral Reefs” (Darwin, 1842)) These methods were not entirely unique or original to Darwin (see discussions by Ruse, 1975, and Thagard, 1977), but his is perhaps the finest and most masterful demonstration of their power over a broad range of questions. Lessons on how to do so can come from the historical sciences that Darwin drew on (such as geology, in which he was originally trained), and which have long wrestled with these challenges
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