The Anatomy of a Mass Extinction

The typical sequence of events in a mass extinction begins with the extinction phase, when biotic diversity falls rapidly. During this time, the extinction rate (the number or percentage of taxa going extinct in any time interval) far exceeds the origination rate (the number of new taxa evolving through speciation). After some period of time, the extinction phase ends and is succeeded by a second phase, often called the survival phase. This is a time of minimal diversity, but no or few further...

Why the Modern Mass Extinction May Not Be as Bad as Projected

One of the great dangers facing those who attempt to prophesy is that estimates, coming from the best of intentions, may become more catastrophic than the data warrant. Extinction is an emotional issue for many of us, even (or especially) scientists, and emotion can color judgment and distort objectivity. There is a very real possibility that estimates of current extinction rates are inflated. Few studies are able to pinpoint how real the threat of elevated extinction rates really is, or how...

Winners and Losers

Predicting winners and losers in the future can be as perilous for biologists as it is for stockbrokers. In both cases, however, there are some clear signs of what may prosper (and even diversify) and what may die out. One clear insight into predicting whether a species will flourish or not comes from the size of its geographic range. In the late 1980s, biologists J. Brown and M. Maurer showed that species of North American birds with small geographic ranges almost always had low population...

The Future of Evolution

What is the future of evolution So ambiguous a question invites varied responses. As in The Time Machine, it might be interpreted in terms of outcomes what will animals, plants, and other organisms be like at some time in the future, perhaps a thousand years from now, perhaps a thousand million years from now The only certainty is that they will be different. Even in the near future, the mix of species and their distributions, relative numbers, and relationships with one another will have...

The Near Past

The Beginning of the End of the Age of Megamammals We are more dangerous than we seem and more potent in our ability to materialize the unexpected that is drawn from our minds. LOREN EISELEY, The Unexpected Universe I hr inland from Cape Town in South Africa, the high rocky ramparts of what y is known as the Great Escarpment have dried the air and created a desert. This region is now home to many sheep and a few towns. The largest of the latter is Graaf Reinett, the self-styled jewel of the...

Hendaye France

Long ago, Spain whirled in its continental drifting, made a hard right turn, and ran into France with a tectonic lunge. Rocks crumbled, and the Pyrenees became the zipper uniting these two great blocks. An ancient seafloor was raised in the process. Today a part of that ancient ocean is exposed for all to see, but like Gomorrah and Sodom, that deep-sea bottom and its trove of skeletons has been turned to stone. Now it is a scenic park on the border between Spain and France, a coastal bit of the...

The Transgenic Revolution Building Weeds

The genetic engineering our ancestors used to introduce new characters into their agricultural crops and domestic animals was crude but effective save the favored varieties and let them breed kill off the others. But in the twentieth century a new type of genetic engineering appeared one that alters the genomes themselves. This new way of introducing novelty is sweeping the agricultural regions of the Earth, and will surely have unintended consequences. It may be that the transgenic revolution...

Disturbance and Diversity

Since the actual number of species on Earth today is so important, knowing what controls that number is also important. Why are there not twice as many, or half as many, plants and animals Why are there more now than during the time of Gondwanaland Although there is an enormous scientific literature on diversity, this is a question that has perplexed biologists for nearly two centuries, and it appears that there is no easy answer. The most famous book on the topic Charles Darwin's On the Origin...

The Cambrian Explosion and the Expectation of Novelty

The history of life, like any history, has occurred as a vector of time. And as in any history, there is never any going back, at least in any meaningful way. Events and their history create irrevocable changes that make each slice of time unique as it passes through the sequence from future to present to past. In the context of the future of evolution, it appears that there will never again be an Age of Fishes, or Reptiles, or Mammals even approximately similar to those that have occurred in...

Lessons from the Past

Mass extinctions are biological events. But they have been transformed into geologic evidence, and therein lies the problem. Turning flesh into stone means the loss of most biological information, and at best we have only the slenderest of clues to the events of that time. Even so, the transition of creatures during the two mass extinctions profiled above can teach us a great deal about how mass extinctions can affect the nature of evolution on the planet. Not only did the composition of the...

Compounded Disturbance and Ecological Surprise

All species have evolved in the presence of disturbance. Thus, disturbances that happen within a particular range of intensity not too extreme result in little long-term change in the nature, composition, and energy flow of a population, or even an ecosystem. But what of compounded disturbances, when major disturbances occur repeatedly at higher than normal frequencies This was the question posed by ecologist Robert Paine and his colleagues in a 1998 article. Paine has spent his entire research...

Characteristics of Domestication

Although most animal species can be tamed, or to some extent habituated to the presence of humans if raised by them from a young age, domestication goes far beyond this simple behavior modification. Domesticating a species requires not only a concerted effort over extended periods of time, but certain pre-existing features of the species in question. In the past this effort was made only for reasons such as enhanced food yield, transportation, or protection from predators. Domesticated animals...

Plate Tectonics and Diversity

The studies above and many others as well suggest that compounded disturbance produced by humanity may have caused the equilibrium level of world biodiversity to drop. Yet there is a second and equally important factor that is taking us back to Gondwanaland the functional removal of barriers to migration. In a way, to borrow from another hoary bumper sticker, we have indeed stopped continental drift. One of the major influences on the equilibrium value of global biodiversity is continental...

Foreword by Niles Eldredge

TIMES BOOKS Henry Holt and Company New York I would like to thank the following people for various reasons Sam Fleischman Diana Blume Rob DeSalle Jill Rowe Kirk Johnson Daniel Heiminder John Michel Kurt Keifer Carl Zimmer Niles Eldredge Andrew Vallely Alisa Tager Jean-Jacques Annaud Tom Sanford Anne Pasternak And I would like to thank my gallerists Jay Gorney, Karin Bravin, and John Lee, and especially Rodney Hill. A.R. Henry Holt is a registered trademark of Henry Holt and Company, LLC....

Measuring Species Diversity

Determining rates of species loss seems straightforward tabulate the number of species living at a given period of time, and compare that number to the number living at other time intervals. Yet there are numerous problems with this seemingly simple methodology. To arrive at extinction numbers, we need an accurate census of the living. Such a global census of biodiversity at the species level is still lacking. No one disputes that the activities of humankind have caused extinctions in the...

Prophecy

The factors described above can be used to pick the potential evolutionary winners of the future organisms adapted to cities or agricultural fields and capable of living in polluted water or air. Much future evolution may be invisible, taking place among already existing animals through changes in behavior and physiology. Can some vision of our world, even a millennium from now, be imagined With apologies to H. G. Wells and to those who require that books about science remain serious and dry ,...