Mark Earl Olson

Biologists energetically debate terminology in ecology and evolution, but rarely discuss general strategies for resolving these debates. We suggest focusing on metaphors, arguing that, rather than looking down on metaphors, biologists should embrace these terms as the powerful tools they are. Like any powerful tool, metaphors need to be used mindful of their limitations. We give guidance for recognizing metaphors and summarize their major limitations, which are hiding of important biological detail, ongoing vagueness rather than increasing precision, and seeming real rather than!gurative. By keeping these limitations in mind, metaphors like adaptive radiation, adaptive landscape, biological invasion, and the ecological niche can be used to their full potential, powering scienti!c insight without driving research off the rails.

Some adaptationist explanations are regarded as maximally solid and others fanciful just-so stories. Just-so stories are explanations based on very little evidence. Lack of evidence leads to circular-sounding reasoning: “this trait was shaped by selection in unseen ancestral populations and this selection must have occurred because the trait is present.” Well-supported adaptationist explanations include evidence that is not only abundant but selected from comparative, populational, and optimality perspectives, the three adaptationist subdisciplines. Each subdiscipline obtains its broad relevance in evolutionary biology via assumptions that can only be tested with the methods of the other subdisciplines. However, even in the best-supported explanations, assumptions regarding variation, heritability, and fitness in unseen ancestral populations are always present. These assumptions are accepted given how well they would explain the data if they were true. This means that some degree of “circularity” is present in all evolutionary explanations. Evolutionary explanation corresponds not to a deductive structure, as biologists usually assert, but instead to ones such as abduction or induction. With these structures in mind, we show the way to a healthier view of “circularity” in evolutionary biology, and why integration across the comparative, populational, and optimality approaches is necessary.

Phylogeography, a relatively new subdicipline of evolutionary biology that attempts to unify the fields of phylogenetics and population biology in an explicit geographical context, has hosted in recent years a highly polarized debate related to the purported benefits and limitations that qualitative versus quantitative methods might contribute or impose on inferential processes in evolutionary biology. Here we present a friendly, non-technical introduction to the conflicting methods underlying the controversy, and exemplify it with a balanced selection of quotes from the primary biological literature, to invite the philosophy of biology community to pay attention to the elements that have played a primary role in its presumed resolution. We also present the basic features of our own metascientific take on the debate, and point out—as a preliminary step in preparation for upcoming, more detailed treatments—the importance that appeals to authority in fields external to phylogeography per se have played in the current status of this highly visible evolutionary biology dispute.

‘‘Adaptive radiation’’ is an evocative metaphor for explosive evolutionary divergence, which for over 100 years has given a powerful heuristic to countless scientists working on all types of organisms at all phylogenetic levels. However, success has come at the price of making ‘‘adaptive radiation’’ so vague that it can no longer reflect the detailed results yielded by powerful new phylogeny-based techniques that quantify continuous adaptive radiation variables such as speciation rate, phylogenetic tree shape, and morphological diversity. Attempts to shoehorn the results of these techniques into categorical ‘‘adaptive radiation: yes/no’’ schemes lead to reification, in which arbitrary quantitative thresholds are regarded as real. Our account of the life cycle of metaphors in science suggests that it is time to exchange the spent metaphor for new concepts that better represent the full range of diversity, disparity, and speciation rate across all of life.

We develop a new metaphor account where metaphors become surrogate variables for different but related phenomena. As we will argue, subrogation is the result of the interplay between the things inspired by the metaphor and the empirical dynamics that result from such inspiration. In particular, we focus on adaptive radiation, a major concept of evolutionary biology. Our study suggests that there is no distinct phenomenon, process, or pattern in nature than can be identified as adaptive radiation. What we have instead is a grouping variable that has surrogated different evolutionary phenomena into one expansive label. We believe this analysis of metaphors helps better understand the value of metaphors for science not only as a provider of epistemic and cognitive virtues but most importantly, as a crucial research tool that can both help and divert scientific experimentation.

Although there is increasing recognition that theory and practice in science are often inseparably intertwined, discussions of scientific controversies often continue to focus on theory, and not practice or methodologies. As a contribution to constructing a framework towards understanding controversies linked to scientific practices, we introduce the notion of borrowed epistemic credibility, to describe the situation in which scientists exploit fallacious similarities between accepted tenets in other fields to garner support for a given position in their own field. Our proposal is based on the analysis of a recent controversy in phylogeography, a biological subdiscipline concerned with the study of the historical causes of variation in genetic diversity within species in concrete biogeographical locations. Through a review of the arguments that support the two conflicting phylogeographic schools, we show that ‘theory’ plays essentially no role as a foundation of the controversy, whereas both sides borrow epistemic credibility from sources such as formal logic, similarity of results to those in other scientific areas, the authority of prominent scientists, or the presumed superiority of quantitative vs. verbal reasoning. Our case study underscores the indivisibility of theory and practice and provide a means to re-examine important philosophical issues such as the meaning of inference, rationality, justification, and objectivity in scientific practice.

Philosophical treatments of scientific controversies usually focus on theory, excluding important practice related aspects. However, scientists in conflict often appeal to extra-theoretical and extra-empirical elements. To understand better the role that non-empirical elements play in scientific controversies, we introduce the notion of borrowed epistemic credibility, illustrating our proposal with a recent controversy in a field of evolutionary biology known as phylogeography. Our analysis shows how scientific controversies that spring from disagreements about methodological issues potentially involve deeper debates regarding what constitutes good science, prompting the re-examination of more general issues, such as the nature of inference, rationality, and objectivity.