THE VIRGINIAN-PILOT
Copyright (c) 1995, Landmark Communications, Inc.
DATE: Sunday, December 17, 1995 TAG: 9512180185
SECTION: COMMENTARY PAGE: J3 EDITION: FINAL
TYPE: Book Review
SOURCE: BY DAVID MONROE
LENGTH: Medium: 80 lines
THE SIXTH EXTINCTION
Patterns of Life and the Future of Humankind
RICHARD LEAKEY AND ROGER LEWIN
Doubleday. 271 pp. $24.95.
The Sixth Extinction is a fascinating examination of the physical evidence and philosophical aspects of mass extinction. The authors, Richard Leakey, the world's most famous paleoanthropologist (and son of Louis and Mary Leakey), and Roger Lewin, scientist and author, thoroughly explore the field research to provide as complete a picture of life on Earth as can be managed in so compact a book.
The topic was driven by Leakey's appointment to the directorship of the Wildlife Conservation Dept., which became the Kenyan Wildlife Services. While in that position, he was charged with the task of halting the destruction of elephant herds on the African plain and thus thrust from a preoccupation with long extinct species to a concern for species threatened with extinction.
According to Leakey, Darwin's theory of natural selection greatly influenced past scientific examination into the development of the species as we know them today. The Darwinian process was defined by gradual change, the accumulation of tiny modifications in behavior or anatomy occurring over a measured period of time and in response to environmental circumstances. Thus the simplification to ``the survival of the fittest.'' But current scientific evidence leads to the possibility that there may be more to the story than this simple idea.
The Burgess Shale, located in the southern part of British Columbia, Canada, produced evidence of species that defied all efforts to link them with any known phyla. They ``burst'' onto the evolutionary scene and disappeared just as dramatically. A long examination there led to the conclusion that the success of species in Burgess did not depend on superior design, improved adaptation and increasing complexity, but rather on chance. The surviving species were lucky.
There have been five mass extinctions (events that resulted in the disappearance of 65 percent to 95 percent of species on Earth) ranging in time from about 440 million years ago to as recently as 65 million years ago, with the end of the Cretaceous period and the disappearance of the dinosaurs. Some common factors have been discovered in global conditions during each of the ``Big Five,'' such as a fall in sea level or global climatic change, particularly cooling. There is even evidence that an asteroid's or comet's impact may have contributed to the end of the Cretaceous period.
But the most notable discovery is that in the aftermath of an extinction, the rebuilding of species does not occur in a smooth and elegant process to duplicate what existed before. The idea of harmony or balance in nature seems to have been replaced by the concept of chaos, with the extinction itself playing an active role in the diversity of resultant species. Stable populations can become dominated by one or a few species and thus be more vulnerable while, in contrast, population fluctuations can drive communities to higher levels of diversity.
Trying to understand why certain patterns emerge rather than others may seem very academic but, as the authors point out, we need to understand which species are vulnerable to extinction and which play such a vital role in their community that their extinction would provoke a cascade of other extinctions.
Homo Sapiens arrived on the scene late in the evolutionary history of Earth, but we arrived with an unsurpassed capacity to devastate diversity. Our reason and intellect have not prevented us from exploiting the Earth's resources in unprecedented ways. The authors ask, ``Can the system be reduced in size through eliminating some species and still be effective?'' We don't know. They ask, ``Which species or groups of species can be removed without detriment to the system which sustains all living things?'' This we know only incompletely.
The degree of ignorance about the natural world upon which we depend is frustratingly large, but it is not total. That there will be a sixth extinction is not questioned, but human beings' ability to survive it may depend on what we know of our place in the world. MEMO: David Monroe is a former town planner for Kitty Hawk, N.C., and owner of
The Island Bookstore in Duck, N.C. by CNB