Mammoth Extinction and Human Hunger

Earlier this year a book caught my eye at my favorite book store: The Call of Distant Mammoths - Why the Ice Age Mammals Disappeared, by Peter D. Ward. This 241-page book is published by Copernicus/Springer-Verlag at $26 in hardcover.

Ward is also the author of other books of note such as: The End of Evolution, and On Methuselah’s Trail. I have not read these other works but after having read this one I will probably read them as well. Why? I was very impressed with Ward’s writing and having read many books by many authors I can assure you that not everyone can write this well.

Peter Ward is Professor of Geological Sciences, Professor of Zoology, and Curator of Paleontology at the University of Washington, Seattle. He has a recent paper with W. Bruce Saunders in the Journal of Paleontology (Volume 71, No. 6, 1997) wherein he establishes a new genus of the living nautiloid cephalopods.

Ward’s premise is to determine a cause for the extinction of the large land animals of the most recent ice age including mammoths and mastodons. It appears from the beginning that he favors the rise of human populations as a major force in their demise. Ward does consider this to be a mass extinction while other authors that I have read do not since its effects were primarily on large land animals.

"The Time Machine", chapter one, begins with Ward taking the reader to three specific and significant times and places in pre-history: 115,000 years before present near the Cape of Good Hope on the coast of South Africa. Here we observe some of the earliest modern humans known; 35,000 years before present on the northern coast of Australia where we see the earliest arrival of humans to this continent; and lastly 11,000 years before present in the American southwest. We see no humans here but only stone spear points amidst drying mammoth bones at an equally dry seasonal lake bed. Ward begins to set the reader’s thoughts to the great human successes in reproduction and technology which have allowed our global expansion at the expense of the lesser creatures.

To really understand the ice age extinction, as Ward states, one has to understand the mass extinctions which have gone before. His second chapter recounts some of the historical work done by early geologists including the first proofs that extinction was a reality and that other life forms had lived and died prior to human creation - Christian teachings at the time allowed for only an initial creation of creatures all perfectly adapted to their particular way of life and that these creatures remained the same for eternity. More modern work is brought forth as Ward discusses his experiences at professional symposia on extinction both here and in Europe. Lastly Ward makes a personal visit to Gubbio, Italy - the site made famous by Walter Alvarez et. al. which provided the first evidence for an impact cause for the end Cretaceous mass extinction.

The chapter entitled "When Worlds Collide" is probably my favorite. This showcases Ward’s writing style and why I am so excited by this book. The subject matter as you may have guessed is the end Cretaceous mass extinction and the extraterrestrial impact which many (including Ward) believe caused it. My exuberance lies in the last half of this chapter when Ward recounts the events before, during, and after the impact. I have read similar accounts many times but Ward is able to paint visual images with his words which make the reader feel he personally witnessed the event.

A portion of this chapter is also devoted to the lively debates surrounding the impact theory. Interestingly, vertebrate paleontologists specializing in dinosaurs appear to be the group most against this agent as cause for dinosaur extinction. They maintain other factors were at work which were producing gradual dinosaur extinctions well before the impact.

It may seem odd that so much space is devoted to the dinosaur extinction in a book about extinction of ice age mammals. It is all part of a well organized plan leading the reader from the best known extinction into the radiation and evolution of the mammals (including us). The following chapters deal in part with the evolution and migration of the hominids plus multiple examples of the extinction of large animals rapidly following the initial appearance of humans in new areas. Parallels are drawn with the Cretaceous extinctions.

Ward presents a multifaceted approach by making detailed presentations of the work of other leading scientists concerning this particular extinction. Paul Martin’s earlier work is discussed in detail as is that of Don Grayson. Martin originated the "overkill" hypothesis implicating rising human populations and over hunting with these extinctions. Grayson and others support climatic change as the driving force behind the ice age extinctions. Both of these theories are extensively discussed. Background information is presented concerning the biology of the animals as inferred from their remains and modern analogues. This is necessary to help the reader evaluate the various extinction theories. In addition, the changes in vegetation and climate, plus their potential effect on the larger animals, is analyzed. This may sound like very dry reading at this point but I can assure you that Ward’s picture painting style mentioned earlier carries through here as well.

Some of David Raup’s ideas from his 1991 book, Extinction: Bad Genes or Bad Luck?, is put to good use in Ward’s "The Kill Curve" chapter. Ward explains Raup’s Kill Curve concept which in part demonstrates that producing an extinction of a species by killing off individuals does not necessarily mean having to kill every last one of them. For any given species there is an extinction threshold. Population numbers below this threshold value doom a species to extinction (sooner or later) regardless of any efforts to save them. Applied to the large ice age mammals, human hunting which reduced the mammoth populations to isolated groups with numbers below the threshold level would produce their eventual extinction.

Ward also addresses the often raised question of "where are the bodies if this is a sudden mass extinction?" The same question is commonly applied to the dinosaurs’ extinction. Ward easily dismisses this apparent conundrum [sorry, I couldn’t help myself] by reviewing modes of fossilization and the probabilities of a mass dying or mass killing (by humans) being preserved in the fossil record.

Ward examines so many differing views it seems he is headed toward concluding with a multi-causal mode. None of the single causes discussed seem to have all the necessary effects to produce the ice age extinction event. Human hunting, climate changes, habitat reduction, and changes in the types of vegetation (the animal’s food supply) all appear to have worked together to produce this particular extinction.

Finally Ward presents his own version of the "smoking gun" which indeed points the finger most directly at human hunting. The information presented is based upon work done with modern elephant and fossil mammoth tusks by Dan Fisher. Briefly, growth rings in the tusks show a tremendous amount about the animal’s age, breeding, and food supply. Fisher’s data indicate that the mammoths were very healthy (therefore climate changes had not caused starvation by affecting food supplies) and were breeding very frequently (this is something modern elephants do when herds are shrinking in size due to predation pressure). The logical conclusion from these data places the blame directly on human hunting.

Ward’s concluding chapter is one with a cautionary message. In essence: humans should learn from past extinctions, especially this one, so that we can act soon enough to prevent further extinctions caused by human activity.

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