Preface to In the Light of Evolution Volume II Biodiversity and Extinction

The Earth's biodiversity is a wellspring for scientific curiosity about nature's workings. It is also a source of joy and inspiration for inquisitive minds, from poets to philosophers, and provides lifesupport services. According to Kellert (2005), biodiversity affords humanity nine principal types of benefit: utilitarian (direct economic value of nature's goods and services), scientific (biological insights), aesthetic (inspiration from nature's beauty), humanistic (feelings deeply rooted in our inherent attachment to other species), dominionistic (physical and mental well-being promoted by some kinds of interactions with nature), moralistic (including spiritual uplifting), naturalistic (curiosity-driven satisfaction from the living world), symbolic (nature-stimulated imagination, communication, and thought), and even negativistic (fears and anxieties about nature, which can actually enrich people's life experience). Whether or not this list properly characterizes nature's benefits, the fact is that a world diminished in biodiversity would be greatly impoverished.

Many scientists have argued that as a consequence of human activities the Earth has entered the sixth mass extinction episode (and the only such event precipitated by a biotic agent) in its 4-billion-year history (Leakey and Lewin, 1995; Glavin, 2007). The last catastrophic extinction, which occurred about 65 million years ago and was the coup-de-grace for nonavian dinosaurs, marine ammonites, and many other evolutionary lineages, happened rather suddenly after a large asteroid slammed into the planet. Today, most of the biotic holocaust is due—directly or indirectly—to local, regional, and global environmental impacts from a burgeoning xv xvi / Preface to In the Light of Evolution, Volume II

human population. The first phase of the current extinction episode started about 50,000 to 100,000 years ago when modern humans began dispersing around the planet. The second phase started 10,000 years ago with further population increases and land-use changes associated with the invention of agriculture. A third phase of environmental alteration and biodiversity loss was ushered in by the Industrial Revolution. E. O. Wilson (1992) estimated that the Earth is currently losing approximately 0.25% of its remaining species per year (such that at least 12,000 species may be going extinct annually). Such estimates are educated guesses because they represent extrapolations (from species-area curves and other evidence) to taxa that undoubtedly are disappearing even before they can be identified and studied. Nevertheless, they do reveal the general magnitude of the ongoing extinction crisis. For many species that manage to avoid extirpation, local and regional populations are being decimated.

The modern extinction crisis is prompting scientific efforts on many fronts. Systematists are striving to describe biodiversity and reconstruct the Tree of Life. Ecologists are mapping the distributions of biodiversity and global hotspots that merit special conservation attention. Paleontologists are placing the current crisis in temporal context with regard to the Earth's long geological history, and also to the recent history of human impacts on biodiversity across timescales ranging from decades to millennia. Educators and concerned scientists are striving to alert government leaders, policymakers, and the public to the biodiversity crisis. Conservation efforts (including those by many nongovernment organizations) are underway to slow the pace of biological extinctions. However, unless conservation achievements accelerate quickly, the outlook for biodiversity in and beyond the 21st century remains grim.

This book is the outgrowth of the Arthur M. Sackler Colloquium on "Biodiversity and Extinction," which was sponsored by the National Academy of Sciences on December 7-8, 2007, at the Academy's Arnold and Mabel Beckman Center in Irvine, California. It is the second in a series of colloquia under the umbrella title "In the Light of Evolution." The first book in this series was titled In the Light of Evolution, Volume I: Adaptation and Complex Design (Avise and Ayala, 2007).

The chapters that follow illustrate current scientific perspectives on biodiversity and extinction across varied timescales and diverse taxo-nomic groups. Chapters are arranged in four parts, each immediately preceded by a brief editorial introduction. Authors in Part I address contemporary patterns of biodiversity and extinction in animals representing several imperiled taxa and environmental settings, and authors in Part II do likewise for various modern plants and microbes. In Part III, authors add historical perspective by addressing biodiversity trends and extinction processes in the near and distant paleontological past. Authors in Part

IV offer their projections for the future of biodiversity given the pace of environmental alteration by human activities. Collectively, the chapters in this book synthesize recent scientific information and ideas about the abundance and threats to biodiversity in the past, present, and projected future.

The current extinction crisis is of human making, and any favorable resolution of that biodiversity crisis—among the most dire in the 4-billion-year history of the Earth—will have to be initiated by mankind. Little time remains for the public, corporations, and governments to awaken to the magnitude of what is at stake. Preserving biodiversity is undeniably in humanity's enlightened self-interest, but the tragic irony is that a majority of humanity is not yet enlightened to this fact. It is hoped that the information and sentiments in this book will assist that critical educational mission.

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