Extinction - Luck of the Draw

Extinction, Bad Genes or Bad Luck?, by David M. Raup, W.W. Norton, 1991, is the topic for discussion in this month's contribution. Raup is a noted invertebrate paleontologist from the University of Chicago. He has also co-authored a number of other books including: Handbook of Paleontological Techniques, with Bernhard Kummel, and Principles of Paleontology, with Steven Stanley. This hardbound volume is $19.95 and may need to be special ordered through a better book store. It may also be available in paperback but I've not seen it.

According to the biographical information about Raup on the dust jacket, he is a statistical paleontologist. His expertise in this field is further mentioned in the Introduction by Stephen Jay Gould. The author uses statistical methods and analogies throughout the book to illustrate his points. This is not done in a highly technical way so you needn't be concerned if you haven't studied statistics. The book is directed at general readers.

As you might have gathered, this work deals with extinction and its potential causes. The author poses the question, " do species become extinct because of some inherent weakness or is it a matter of being in the wrong place at the wrong time?" Numerous paths are taken in pursuit of the answer, both with historic as well as prehistoric examples.

The first two chapters put extinction in perspective and cover the history of life. The author begins with the chilling estimate that 99.9% of all species that have ever lived are now extinct. He also reinforces one of Gould's favorite statements concerning the unpredictability of a pattern existing in the evolution of life; in other words, the Victorian belief of progress through evolution toward more complex and better life forms, culminating with man, has no basis in fact.

Chapter three is the one most heavily involved in defining statistical principles. All is done in a non-threatening way for the general reader. Concepts of randomness are defined using a principle known as "gambler's ruin". Raup also explains that the randomness of a coin flip is dependent upon making assumptions and intentionally ignoring any number of variables. In doing this, he illustrates the old adage, "you can prove anything you want with statistics". This section also discusses skewed data versus the normal distribution and differing extinction and speciation rates. This isn't heavy duty statistics, no mathematical formulas to worry about. The principles discussed are used throughout the rest of the book to explain the points made so you will have to understand them.

Succeeding chapters deal with mass extinction, selectivity of extinction, search for causes of extinction - biological and physical. Mass extinctions are defined as those wherein 65% or more of the species become extinct; these grade into lesser and lesser events ending with background extinctions which can't be differentiated into specific occurrences. The Pleistocene extinctions of most of the large animals is shown to be a statistically significant happening but not a mass extinction. In dealing with selectivity, specifically with the trilobite extinction at the end of the Paleozoic, Raup concludes that their demise was not a random occurrence; some as yet unknown reason exists for their loss.

During the discussion of biological causes for extinction, the author emphasizes the resilience of species and downplays the fragile delicate ecosystem "stereotype" commonly presented by the media and some environmentalist extremists. He follows this with an historic extinction event of the heath hen in New England to illustrate a number of points: the "first strike" that initially reduces the geographic range and small population sizes that are more susceptible to extinction.

Raup devotes an entire chapter to the K-T mass extinction which eliminated the dinosaurs. The impact theory is discussed at length including cratering rates, destructive power, and periodicity. This book was published just prior to the confirmation of the Yucatan crater as the "smoking gun" at the K- T boundary, but mention was made that it was being investigated as such. The following chapter presents a discussion of the probability that all extinctions are caused by meteor impacts.

Finally the author summarizes and then discusses the role of extinction in evolution. If there were no extinction, would there be any evolution? Raup concludes with an answer to his "bad genes or bad luck?" question (you'll have to read the book) and some notes on extinction today.

While the book doesn't deal heavily in fossils per se, I believe that it is a worthwhile book to read. It will give you a much broader and current view of extinction than most general books on paleontology.