Building a hierarchical framework on the foundations of darwinism

Building a hierarchical framework on the foundations of Darwinism
DAVID B. WAKE - Nature 416, 787 - 788 (25 April 2002
Museum of Vertebrate Zoology, University of California, Berkeley,California 94720-3160, USA.
The Structure of Evolutionary Theory
by Stephen Jay Gould
Belknap: 2002. 1,464 pp. $39.95, £27.50, 45.90 euros
We live in a darwinian world. For many evolutionary biologists the ever-extending grand evolutionary synthesis promulgated in the 1930s and 1940s offers adequate explanations and serves as a consistent generator of testable hypotheses. For Stephen Jay Gould it is but a foundation, wholly inadequate to be a framework within which to build. Evolution proceeds in a hierarchical manner, so proper analysis requires a hierarchical approach, Gould believes.

Modern darwinians, being largely reductionist in approach - while paying some lip-service to the possibility of constraints, the reality of mass extinctions and the like - view evolution in general as microevolution plus lots of time and some contingency. Gould strongly rejects this perspective. His views are well known, but they have had surprisingly little effect on some of the core disciplines in evolutionary biology, such as population, and quantitative and evolutionary genetics, whose practitioners see themselves as defenders and extenders of the darwinian message. In The Structure of Evolutionary Theory Gould makes a direct, intellectually rigorous argument that a hierarchical perspective would not only enrich modern darwinism, but that it is essential. This book is a manifesto for a new kind of evolutionary biology, one that makes full use of many kinds of knowledge as well as diverse 'ways of seeing'.

This large book demands attentive reading. Gould uses many more words than most writers and the book appears not to have been edited at all. Those who enjoy Gould's erudition and style will find this to be a stimulating and illuminating book; it will infuriate others. There are intellectual wars in progress in the evolutionary-biology community, but most researchers seem to care little about battles engaged around issues such as hierarchical versus reductionist approaches, and structuralist versus functionalist versus historical perspectives. I believe that these are important issues, and that in the long run evolutionary biology will have to confront them. Gould's book, an intellectual tour de force and a work of serious scholarship, will be a permanent factor in the struggle to understand how life has evolved.

Gould knows the book is long and daunting and has supplied readers with a kind of abstract, itself 89 pages long. In this opening chapter he previews, but cannot really encapsulate, the many deeply analytical historical and philosophical treatments to come. This is a long and circuitous argument that new knowledge and new macroevolutionary explanations have been so substantial that a full exposition of evolutionary theory within the domain of darwinian logic "must be construed as basically different from the canonical theory of natural selection, rather than simply extended". This point is made repeatedly throughout the book, lest anyone miss it.

The strategy is to examine the historical roots of evolutionary theory in great detail and to show how earlier workers, even Darwin (but excluding Wallace, who remained the ultimate pan-selectionist), were forced to resort to hierarchical thinking at some point in their intellectual journeys. The book is a veritable history of evolutionary biology, but not all of it, of course. Gould sets the agenda and discusses what he wishes from his point of view: that of a strong advocate for an expanded and greatly modified evolutionary theory.

All Gould's familiar arguments are here, with emphasis on levels of selection, punctuated equilibrium, and their contribution to the development of Gould's hierarchical perspective. His points are forcefully made, but the arguments of only some of his detractors are considered. Gould makes a convincing case for the "hardening" of the adaptationist perspective during, and especially at the end of, the grand evolutionary synthesis in the middle of the twentieth century. He charges that evolutionists became almost blindly channelled. Selectionists will complain that their position is oversimplified.

In a time when we are in something of an intellectual revolution in our understanding of species and species formation, Gould is unrelentingly stubborn in his insistence that speciation is a big deal, that species are individuals, and that species selection is the critical keystone of a hierarchical approach. Close study of species formation has made me question the reality of species as bounded entities, and I am wary of the perspective that species are individuals. I find clade selection an attractive and more general alternative to species selection, but Gould will not give ground. Many of us are attracted to aspects of punctuated equilibrium, and the concept has stimulated much research over the past 30 years. But the insistence that it is a theory of the deployment of species over time and space makes many uneasy and leads to doubts that it is the core concept for the new hierarchical theory of evolution.

I thoroughly enjoyed many parts of the book, for example the long and rewarding chapter on the evolution of development with its strong focus on the positive evolutionary effects of constraints, and the concluding chapter that deals extensively with spandrels. The structuralist message of these chapters is strong and clear, but it is integrated with functionalist and historical perspectives as well. Parallel evolution is given the attention I believe it merits, and Gould does an admirable job of showing why it is important. A fan of Hox genes (he loves the word 'hoxology'), Gould also shows the importance of developmental genetics for his hierarchical perspective and for understanding the evolution of form in organisms.

Gould, the most widely known evolutionist of our time, has remained active in research while at the same time communicating his evolutionary message to the public through his prolific writings and appearances. This book demonstrates that he is not just a popularizer, but a major intellectual force in his discipline. Yet one can predict a strong negative reaction because the book is annoyingly self-congratulatory and self-serving. But what can he do? He is certain that he is right! A strength, and at the same time a weakness, of this book is that the author's powerful personality emerges on nearly every page. The important messages of this book are appreciated most fully when the reader accepts and enjoys the idiosyncrasies of this extraordinary man.