John C. Avise - Conceptual Breakthroughs in Evolutionary Genetics: A Brief History of Shifting Paradigms

The study of the history of a field is the best way of acquiring an understanding of its concepts.

It is helpful for both students and professional biologists if the concepts and theories that form the basis for our understanding are put into the context of how the field has developed over time. It is also arguably more fun to learn things if we understand why particular problems have stimulated the curiosity of biologists or how technical advances made new discoveries possible.

Science is ill suited for people who demand eternal truths. Scientific lessons preached by one generation often seem doomed to be modified if not overturned by the generations that follow. All active sciences are ever changing, but perhaps nowhere has this been certifiably truer than in the field of evolutionary genetics. Hardly a month now goes by without the announcement of some substantial discovery in evolutionary biology or genetics that forces us to rethink what we thought we knew about natures operations. The grandest scientific breakthroughs may bring fame (such as Nobel Prizes) to their authors, but lesser findings are important too because their cumulative effects may alter the trajectory of a discipline.

In 1962, the philosopher of science Thomas Samuel Kuhn published a book The Structure of Scientific Revolutions that itself promoted a revolutionary notion: science progresses not in a continuous linear fashion but rather via paradigm shifts in which the scientific community in response to contrarian evidence and a shifting consensus of opinion eventually abandons conventional wisdom and replaces it with a competing account of reality. Each such paradigm shift constitutes a scientific revolution. How well the Kuhnian worldview generally characterizes science is debatable. It certainly applies in some cases, but many other keystone discoveries (such as the Nobel Prize-winning invention of the polymerase chain reaction [PCR], or the elucidation of DNAs double-helical structure) seem to be singular scientific breakthroughs that did not overturn any particular conventional wisdom on the topic. Regardless of exactly how science unfolds in practice, change it does, often quite inexorably. What was taught to me as a graduate student in the early 1970s would bear scant resemblance to a comparable program of Paradise Lost.

This book highlights 70 conceptual paradigms in evolutionary biology and genetics that were challenged (and in many cases subsequently abandoned or modified) following landmark discoveries that superseded scientists prior understandings of nature. Not all of these paradigm shifts conform strictly to the Kuhnian model, but each does represent a major alteration of scientific attitudes before versus after the path-breaking finding(s). In this book, the 70 paradigm shifts are arranged chronologically by their approximate or exact date of occurrence. Each short essay is presented in the following format: the standard paradigm at that time (i.e., the paradigm that would be lost); the ensuing conceptual revolution; a subjective paradigm-shift index (PS-score) followed by a brief explanation; and a few key references and suggestions for further reading (arranged chronologically) from the relevant literature.

The PS-score can range from 1 to 10, with higher numbers indicating greater overall impact on the field. Thus, each assigned PS-score represents my attempt to integrate several considerations: the revolutionary nature of the new scientific worldview; its veracity (the strength and durability of its supporting evidence); the temporal duration of its impact to date (thus biasing in favor of earlier discoveries and biasing against more recent ones, all else being equal); and the scientific breadth of the new paradigms implications. By assigning a less than perfect score to a given paradigm shift, in no way do I mean to belittle its importance all of the conceptual conversions discussed in this book rank among the most profound insights in evolutionary genetics over the past one-and-a-half centuries, but some surely were more consequential than others.

I wrestled with several alternative ways to categorize the conceptual breakthroughs so as to embrace the great heterogeneity among the discoveries. For example, some of them were revolutionary ideas for explaining longstanding observations (e.g., Whose Handiwork?, Organelle Origins [readers to formulate their own classification scheme for the 70 breakthroughs. Such an exercise might be particularly interesting for historians or philosophers of science.

In the end, I divided this book into four parts based on chronology. Part I deals with discoveries in the first 50 years following Darwin (18591910); Part II treats various breakthroughs over the next 50 years (19101960); Part III covers the 1960s and 1970s; and Part IV covers the modern era, post-1980.

I will not be too disappointed if this book provokes or even irritates some readers, because different evolutionary geneticists inevitably will have differing opinions about what merits inclusion as a salient paradigm shift in the field. I have tried to be inclusive in my choice of topics and discoveries, but for readers that remain disgruntled, all I can suggest is that they themselves try to add, subtract, or differently rank various scientific discoveries from the list. Nevertheless, I do apologize to any practitioner who may feel that his or her own paradigm-busting work has been unduly neglected.