Back to the Future

Authors


Antelopes, Deer, and Relatives: Fossil Record, Behavioral Ecology, Systematics, and Conservation. Vrba, E. S., and G. B. Schaller, editors. 2000. Yale University Press, New Haven, Connecticut. 341 pp. $65.00. ISBN 0-300-08142-1.

This edited volume resulted from a workshop in which the goal was to integrate understanding of the evolutionary past of a group of mammals—essentially the suborder Ruminantia of the order Artiodactyla—and how that knowledge can be used to conserve its members in a rapidly changing world. It is hard to imagine more qualified editors, given Vrba's background in paleontology and Schaller's long experience with field natural history, behavior, and conservation. That all 23 authors who contributed to the book are well-recognized experts in their respective fields ( a virtual Who's Who of artiodactyl research ) raises high expectations for the book.

In some respects the volume achieves its goals admirably. It is a valuable compendium of the paleontological record and phylogenetics of the group, including both morphological and molecular evidence. Gatesy and Arctander's chapter 9 is a particularly informative review of the phylogeny of Ruminantia based on molecular evidence. For large-mammal researchers, the book is worth acquiring for this material alone. In its use of the past as a lesson for the future, however, it is less satisfying. I had hoped this book would squarely face the future and consider the question of what comes now. How will the evolution of this group likely play out in the altered world of the future, given what we know about its evolutionary past?

The book ends instead with the usual lamentations about the human impact on the globe and how we should mend our ways. The future is addressed by looking to the past, which we all wish could be preserved in more of its former, or even current, richness and extent. But, human impacts are not going to lessen anytime soon and promise to grow even larger.

Part of the problem is that the chapters are a somewhat eclectic set that doesn't build progressively though the book to a final synthesis. The organization of the book into three parts, Past, Present, and Future, does not work well because the distinction between past and present is nebulous. Of the 10 chapters on the present, 5 primarily concern phylogeny, and several others contain substantial material on phylogeny. This book is mainly about the past and as such serves ecologists and conservation biologists well, for this is scattered literature not easily assembled by nonspecialists. This will be a major reference volume on the fossil record and phylogenetic analysis of the group.

The reader is rewarded by some intriguing diversions. Examples include chapter 6 by Solounias et al. about scratches and pits on teeth and what they can tell us about diet; chapter 7 by Guthrie, who uses Paleolithic art to show how some extinct species looked in life (aspects lost in fossils and molecular genetics); chapter 11 by Jarman, who points out that, with reference to dimorphism, selection operates on females as well as males; and chapter 16 by Estes on female mimicry of male secondary sexual characters. These chapters make fascinating reading, even if their connection to the stated theme of the book is obscure. Rummaging in the attic is often more fun than the official house tour.

A consistent problem with the phylogenetic studies is the variation in outcomes between different techniques. Morphological evidence that appears to be strong because of conservatism is sometimes contradicted by molecular evidence. Which is right? More disturbing, if either can be wrong then both can be wrong, even if they are in agreement. We can more easily accept the failings of morphological evidence because dating is a problem, and whole taxa may be missing from the fossil record, which we realize is spotty. This is an ever-present theme in the early chapters on the fossil evidence by Gentry, Janis, and Webb. We expect molecular evidence to be more reliable, but it is good to be reminded that gaps in data filled by quantitatively sophisticated software can be every bit as imaginary as paleontological musings over scattered scraps of teeth and bones.

As with any comprehensive work with so many contributors and such a breadth of material, this book contains many things with which some readers would take issue and others that are beyond the reader's expertise. I could not critique the chapters on fossil analysis, and I am thankful I don't have to remember all the technical terminology and Latin names. The comments I make on other chapters that I feel more qualified to critique are often about methods or philosophy of science. For example, I found Solounias et al.'s chapter on scratches and pits in teeth and the herbivore's diet a fascinating method with potentially wide application to questions of diet. But I wondered why they didn't do a discriminant-function analysis of the raw data on scratches and pits and subsequently examine the plots according to the typical diets of species. Classifying species first as grazers or browsers and then making a scatter plot of the means by species has several problems. It masks variation by using only the means by species, and it requires a strict dichotomy of diet when many species ( and individuals ) fall across diet categories. The problem of treating variables by categories is further illustrated by their treatment of an outlier, the bighorn sheep, which has a notable high number of pits. They create the category of “mountain grazer” to cover this exception. Still, they note that the high number of pits is probably the result of inadvertent ingestion of grit. If this explanation is correct then the “mountain” part of the descriptor is irrelevant, and ingestion of grit is the variable of interest. Nevertheless, I'm convinced by their conclusion that fossil giraffids showed browsing, grazing, and mixed-diet habits, but I would still prefer a more continuous scale and carrying variance through the analyses.

Another area where categories create mischief is in taxonomy. I recognize the necessity of such boxes for organizing a bewildering array of organisms and wish everyone would remember that they are matters of convenience, not a true representation of nature. Genetic lineages are complex and not always easily reduced to a single box, instead teetering on the edges between boxes. The problem is not with what is happening in nature but rather with our system of logic, which has no room for transitions. Grubb ( chapter 10 ) and Geist ( chapter 12 ) raise some of these issues about processes of evolution, and I strongly agree with their views on the complexity of evolutionary change.

In chapter 12 Geist puts forward many intriguing propositions, based mainly on broad-scale patterns, and creates a rich description of large-herbivore evolution ( also see Geist 1997 ). This approach capitalizes on his immense knowledge of natural history ( a dying proficiency that, along with others, I lament ), but at the same time it is limited by being based primarily on how well things fit a pattern. At times the fit is convincing and at other times less so. I believe that patterns are better viewed as questions than answers, and I would prefer better quantification to allow a more critical evaluation. For example, Sinclair ( chapter 17 ) gives simple scatter plots for body size and variables that structure bovid communities in Africa that are easily evaluated by eye. In the absence of quantification it is hard to evaluate the strength of a pattern. Furthermore, with small sample size correlations might be spurious, and even with strong correlation the interpretation of cause and effect is still difficult. This book repeatedly deals with this problem with reference to whether similarity is due to common ancestry or convergence. I am not so confident about patterns as adequate evidence, and I think they need to be tested by reductionist approaches if possible, and taken with a grain of salt if not.

In their introductory chapter, Vrba and Schaller note that biogeography—vicariance and dispersal, particularly across exposed land bridges—was more prevalent than speciation and extinction as an artiodactyl response to fluctuating climates during the Pliocene and Pleistocene. This is a comparison I wish were more completely developed. Certainly some taxa were conserved largely unchanged over long time periods, and others were modified in minor ways, such as body size. Speciation was common under some circumstances, however, as revealed by Grubb's analysis of morphoclinal evolution ( chapter 10 ), Geist's discussion of glacial advance and retreat and speciation ( chapter 12 ), Webb's review of New World radiation ( chapter 4 ), Eisenberg's review of the South American radiation of cervids ( chapter 13 ), Sinclair's explanation for the elaboration of the bovid fauna in Africa ( chapter 17 ), and Groves and Schaller's and Amato et al.'s examination of a muntjac radiation in Southeast Asia ( chapters 18 and 19 ). Two key variables continually emerge in the discussion of high rates of speciation: the opening up of opportunity by excess resources—whether by newly created habitat or by the absence of competitors and predators—and fragmentation and redistribution of habitats that result in allopatric populations. Presumably, reproductive isolation in these populations results in genetic drift ( small populations ) or strong directional selection due to changing conditions and thus speciation.

The reason these questions are so important is that they bear directly on the future of these large mammalian herbivores in the face of continuing change. If future changes continue current trends (as is likely), then fragmentation of habitats ( curiously, the concept of metapopulation is not mentioned at all in the book ) and reduction or elimination of competitors and predators will characterize future environments. Thus, it could be argued that these are exactly the processes that fostered speciation in the past. Biogeographic processes as such, it is true, will probably be eliminated by the human matrix. But to a considerable extent this will be overcompensated for by translocations and inadvertent introductions, which result in a different kind of biogeography that probably exceeds in effect the previously natural one—at least for nonvolant mammals.

Herein lies the conundrum for conservation in the future. We have long differentiated natural selection from artificial selection ( i.e., that directed by humans ), but this distinction is no longer possible. Although humans arose some 1 million years ago, it can be fairly argued that they long had a minor impact and were themselves largely “natural.” Klein ( chapter 8 ) reviews the evidence for a human contribution to the high rates of extinction of large mammals during the late Pleistocene and suggests an intermediate position between a major influence, as advocated by Paul Martin, and a minor influence in relation to that of climate change, as advocated by Russell Graham. With this uncertain exception, however, geomorphic processes and climate continued to be the only important drivers of evolution over most of the human period. But since the industrial revolution, and particularly since the recent globalization of human activities, anthropogenic forces rival geomorphic process and climate as drivers of evolution. Already, it is impossible to separate human from natural effects on climate. Can human effects on tectonics be far behind? Inadvertent ( passive ) artificial selection is already thoroughly melded with natural selection; it's already too late to prevent. In principle, we can still control active artificial selection ( although it is unclear that we are up to the job in practice ), and Geist (chapter 22 ) makes important points about this issue as influenced by wildlife management systems.

As conservationists, we are judgmental about human-induced changes, and I've contributed my share to the hue and cry. Still, change is inevitable, driven by both human and natural forces, and, as Sinclair notes ( chapter 17 ), evolutionary history does not repeat itself and neither does human history. Consequently, if we create a future world consisting mostly of human-shaped environments, it is further true that human-influenced evolution of plants and animals will be the inevitable adaptive outcome. Current conservation paradigms are rooted in stasis ( if not in reversion ); they are unable to accommodate to change. Developing new paradigms that incorporate change, then, is the challenge facing conservation in the future. I recommend Antelopes, Deer, and Relatives as providing a strong start for grasping the lessons of the past as they relate to the future. But, it is only a start. The hard evaluation, debate, and creative thinking about conservation beyond our current judgmental paradigms have just begun.

Ancillary