Problems in biology, in sharp distinction to those of philosophy, are solvable—or so writes Mark Ridley in the preface of The Problems of Evolution. Ridley has organized his book around a series of ten great problems currently (albeit, he says, timelessly) besetting evolutionary biology—problems which curiously decrease in their apparent solvability quotient as one ascends the scale of biological organizational complexity and, at the same time, approaches the end of the book. Ridley's preoccupation with the answers to questions imparts an eerie quality to his narrative. On the one hand, he is often quite sure of having the answer to a particular problem (namely, the gene is the unit of selection)—a sort of certainty that I had thought was no longer fashionable in science in general (and particularly in the domain of evolutionary studies, justly known for its authoritative imaginary tales). Yet, I must admit to some frustration when Ridley throws up his hands and announces that a problem still defies solution and that, in fact, our understanding remains at the same low level attained in earlier days. It seems to me that rather more progress has been made toward resolving some of the confusion in evolutionary biology than Ridley seems willing to concede.
Whence this collision between certitude and confusion? Ridley's book accurately reflects the generally unsettled state of evolutionary biology—and I think David Hull is right in laying the blame on a pervasive "common sense" ontology that lies at the very core of evolutionary biology. Thus, certitude stems from unexamined convictions on the very nature of such entities as genes, organisms, demes, species, and taxa of higher categorical rank. And confusion ensues if we have our ontology wrong. Ridley's discussion of what species are—a stunning rerun of the Dobzhansky-Mayr position enunciated nearly fifty years ago—forms the crucial case in point. In this view, species are seen to be simultaneously reproductive communities and at least fairly coherent groupings of similar organisms, recognizably distinct from other such groups. Ridley thus is forced to repeat the standard claim that species are "real" at any one time (especially well demarcated in sympatry with close relatives) but, through time, of necessity will disappear, evolving themselves out of existence as they transform into descendants. Species exist only in a single time plane—a conceptualization that understandably outraged George Gaylord Simpson.
Thus, in our received ontology, species are real, individualized entities when construed as reproductive communities at any one time; they are also classes of similar organisms. Moreover, the economic adaptations of organisms (the main source of that similarity) are imagined to be in a constant state of overhaul, and so the properties of the members of the class change, and a species evolves itself out of existence. Ridley simply does not report that Ghiselin and Hull over a decade ago pointed out that entities are either classes or individuals and that there is no real trick to seeing species, if construed as reproductive communities, as individuals in time as well as in space. Species emerge as spatiotemporally bounded historical entities, regardless of how much or little adaptive modification may accrue in the phenotypes of their component organisms. Much of the doubt and confusion permeating the second half of Ridley's book stems directly from his certitude over the basic nature of species, based, as it is, on a rather garbled ontology.
Indeed, Ridley's book is an excellent statement of mainstream evolutionary biology today. If it does not expose the real problem in evolutionary theory—the ontological issues—it does paint an accurate picture of the teleological-ridden "who or what benefits" approach that selectionists seem ever more locked into as a source of explanation for all manner of biological phenomena. Nor is Ridley utterly conventional: indeed, within the overall matrix of neo-Darwinian theory, he follows the Williams-Dawkins reductionism that sees the gene as the locus of evolutionary action. And, in an amusing and effective gambit that coincides well with my own prejudices, Ridley discusses systematics by contrasting phenetics and cladistics, claiming that the latter is evolutionary and the former not—and allowing him to brush aside the vast middle ground of "evolutionary systematics" as an uninteresting muddle of the two extremes. Moreover, while Ridley is clear that cladistics does not depend upon any prior theory of how evolution actually works, in several places he makes a link between nested patterns of resemblance linking up all elements of the biota and the simple notion of descent with modification. Those nested patterns of similarity have always been the strongest evidence that life must have had an evolutionary history, and it is refreshing to see it acknowledged once again, just as a creation-minded journalist in the United States, in a feat of literary legerdemain, has recently tried to show how cladistics somehow throws doubt on the very idea of evolution.
Ridley's book is not a "fun" read. Indeed, it is difficult to determine to whom this book is addressed. The style, superficially zesty ("And the prediction is this. . . . Here is the final result"), is actually rather flat and utterly matter-of-fact. There seems, for Ridley, to be no joy in these rather marvelous mysteries. The level is decidedly elementary—as if the intended audience were beginning students or the ever-elusive "intelligent layman." Yet, the tone is so unrelentingly serious and the pace so brisk that all but the most dedicated will surely flag.
Nor does the book get at what I think is really the matter with evolutionary theory. But as a quick yet pretty accurate summary of most of the current topics under debate, and as a source of insight into how the majority of evolutionists still approach their topic, the book should prove useful indeed.