Volume 15, Number 2

News, Views, and Reviews

Neo-Darwinism Weighed and Found Wanting

"The Genetics of Adaptation: A Reassessment", American Naturalist

H. Allen Orr and Jerry A. Coyne. 140: 725-742, November 1992

Jerry Coyne (Department of Ecology and Evolution, University of Chicago) and H. Allen Orr (Center for Population Biology, University of California, Davis) have "unexpectedly" -- their adverb -- found "that there is little evidence for the neo-Darwinian view." In this paper Orr and Coyne argue that the neo-Darwinian emphasis on mutations of small effect "is not strongly supported by evidence."

While noting that they are not "macro-mutationists" (a dreaded label that can get one banished from the circle of respectable Darwinians), Orr and Coyne stress that evolutionists do not actually know, either by theory or observation, that mutations of small effect have played the only (or even dominant) role in the origin of adaptations. Indeed, the central theme of their paper stresses how little is known about this matter. Discussing Russell Lande's micro-mutational theory, for example, they write:

We simply have no information here. We do not know, for example, whether mutations adding four bristles to a fly are more than four times as harmful as mutations adding only a single bristle (p.731).

This theme of nescience continues: "Genetic analyses of adaptive differences ... are surprisingly rare (p. 733) ... We simply do not know enough about adaptations within species to allow any conclusions (p. 734) ... our major conclusion -- that there are surprisingly few rigorous genetic studies of adaptation -- is surely correct" (p. 738).

These judgments may prompt a reflective moment in the non-evolutionist observer. What then was all the heat and rather less light, the non-evolutionist might ask, in the fierce debates about neo-Darwinism within evolutionary theory -- if, in the end, so little was in fact known about the genetic basis of adaptation? Did the ferocity of the debate stem from real knowledge about evolution or from its relative absence?

Orr and Coyne call for armchairs to be vacated and soapboxes abandoned. The genetics of adaptation, they write, "is an empirical question that can only be settled with data." But what if mutations of large effect turn out to be insufficient? We hope that Orr and Coyne will consider that some other current certainties (such as the common descent of all organisms by naturalistic mechanisms) may also have to go into the skeptical balance pan to be weighed.

A Philosophical Browser's Paradise


Organized and moderated by Werner Callebaut, Chicago:University of Chicago Press, 1993; 553 p.

All the real work at scientific and philosophical meetings, one often hears, gets done in hall-ways between lectures or at restaurants in the eve-nings. Forget about the announced program. What you really take home will not be found on the official schedule. It's in the informal discussions.

This book, a well-edited series of conversations with leading philosophers and biologists seems to take as its point of departure the significance of the informal spoken insight. Although Plato's Socrates may not fully resemble the Socrates of history, we can be pretty certain that oral dialectic was the preferred method at the birth of Western philosophy.

Thus Werner Callebaut (a Belgian philosopher of science) wasn't falling very far from the Greek tree when he persuaded the likes of biolo-gists Richard Lewontin and Richard Levins or philosophers Michael Ruse and Elliott Sober totalk with him at length about their views on such subjects as the mind, reductionism or the crea-tion/evolution controversy. Armed with a tape recorder, a good knowledge of the literature, and a list of questions, Callebaut originally obtained and used the interviews for a series of radio broadcasts.

However, on reviewing the transcripts, he realized that the results could be edited together into something transcending his first intention.

The participants were then allowed to revise or expand their remarks, making the final product partly actual transcript and partly later revisions (albeit conversational in tone). Callebaut also includes biographical sketches and photographs of each participant.

The book is a browser's dream, marked by a fair amount of gossip and blunt talk. It's clear that philosophers Bruno Latour and Philip Kitcher, for example, both at the University of California, San Diego, have little affection for each other's ideas. The topics on the table for all participants flow (somewhat loosely) from the "return of naturalism:"

Naturalism as a philosophical movement claims that whatever exists or happens in the world is susceptible to explanation by natural scientific methods; it denies that there is or could be anything which lies in principle beyond the scope of scientific explanation (p.xv).

While naturalism of this sort may gladden the hearts of many readers of OR, it will bewilder or infuriate many others. For those readers, moving through this book is therefore like a visit to alien territory and quite useful for seeing what a philosopher means when he claims to be able to explain (for instance) how moral categories evolved, how our knowledge of the world has an evolutionary basis, or how the mind can be reduced to neurophysiology.

For the non-evolutionist it is remarkable how broadly evolutionary theory is seen (by these participants) as informing one or another aspect of scientific or philosophical knowledge. Remarkable, or perhaps frightening: how could a theory so plagued by difficulties (from the non-evolutionist's perspective) pass muster with otherwise very bright and skeptical thinkers?

The answer must lie with the power of the premise of naturalism. It is the Archidemean point on which the rest is moved. Reject naturalism, and the evolutionary understanding of the world is soon to follow. Retain naturalism, and evolution is indispensable.

File Date: 7.20.95