- The Washington Times - Monday, December 16, 2002

The concept of extinction is fairly recent.
In 1796, the great French comparative anatomist Georges Cuvier analyzed the elephant family and concluded that the Indian and African elephants were two different species.
Then he demonstrated from fossil bones that the woolly mammoth was also a separate species. That an animal so large could exist unnoticed in some out-of-the-way corner of the Earth would be inconceivable, Cuvier said. The only possible conclusion was that it was extinct.
Cuvier was not the first scientist to bring up the idea of extinction, but he was the first to offer detailed and convincing evidence that it took place in the course of nature. It was a revolutionary finding. At that time, most Western science subscribed to the "great chain of being," in which creation was perfect, infinitely divisible and no species were missing since Noah apparently misplaced the unicorns.
Thomas Jefferson described it succinctly in his 1784 "Notes on the State of Virginia" when he wrote: "The bones of the mammoth, which has been found in America, are as large as those found in the old world. It may be asked, why I insert the mammoth, as if it still existed? I ask in return, why I should omit it, as if it did not exist? Such is the economy of nature, that no instance can be produced, of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken."
In 1803, as the third president of the United States, Jefferson sent Meriwether Lewis into the wilderness of the newly purchased Louisiana Territory advising the explorer to keep an eye peeled for mammoths. He thought the great beasts still might be at large in the unexplored vastness of the American continent. Lewis and William Clark found no such animals, and Jefferson's quest for a live mammoth came to an end.
Cuvier's revolutionary work fired the imagination of his generation. Honore de Balzac wrote: "Have you ever been cast forth into the immensity of space and time while reading the geological works of Cuvier? Carried by his genius, have you ever soared over the limitless abyss of the past, as if supported by the hand of an enchanter? Discovering from period to period, from bed to bed, in the quarries of Montmartre or the schists of the Urals, animals whose fossilized remains belong to antediluvian civilizations, the mind is terrified to perceive the billions of years, the millions of people that the feeble human memory, that the indestructible divine tradition has forgotten. Is not Cuvier the greatest poet of our century?"
The modern 12-year-old populates "antediluvian civilizations" with the flesh-ripping dinosaurs of Jurassic Park. But in Cuvier's day, mammoths and their kin the elephants, the largest extant land animals, ignited the imaginations of schoolchildren and scientists alike. The subject is not as scientifically exciting now, but W.H. Berger of the Scripps Institution of Oceanography in San Diego argues for more attention to it.
"Mammoth extinction deserves a special place in paleontology textbooks," he writes, "and should not be suppressed in favor of dinosaur extinction."
The mammoth is relevant to the modern world in another, more sinister, way: It may be the first animal to have been driven to extinction by advancing technology deployed by humans, it may have been driven to extinction by severe climate change, or "hyperdisease" may have contributed to its extinction.
In any case, the fate of this giant from the Pleistocene Epoch provides obvious modern lessons to be puzzled out. We live, after all, in an era of warming climate, with advancing disease fronts, amid technologies notable for their adverse impact on biological diversity.
The thesis perhaps most popular among archaeologists, in the New World at least, is that about 11,000 years ago, humans crossed the Bering Land Bridge, migrating from Siberia to Alaska in relatively large numbers with a new hunting technology: the Clovis, or spear. Within a thousand years after the arrival of these well-armed humans, mammoths and mastodons had disappeared.
In a recent paper in the journal World Archaeology, University of Nevada-Reno anthropologist Gary Haynes wrote: "Archaeological and theoretical evidence indicates that Clovis-era foragers exterminated mammoths and mastodons in North America around 11,000 radiocarbon years ago. The process unfolded quickly as human foragers explored and dispersed into fragmenting habitats where megamammal populations were ecologically stressed."
Paul Martin at the University of Arizona's Desert Laboratory outside Tucson has modeled this hypothetical extinction. With about 3.4 million mammoths likely roaming the continent, Mr. Martin assumed a 1 percent growth in the human population and a "mammoth biomass of 5,000 pounds per square mile." This would factor out to a mammoth every four square miles or so.
The hunters would advance along a southward-expanding front, doubling in numbers every 70 years and killing six mammoths per hunter. "In 532 years a total population of 90,000 people will have destroyed a mammoth-mastodon herd of 3.4 million animals. The front of hunters invading the continent will have spread from southern Wyoming to southern Arizona in 120 years."
Increasing the rate of human population growth to 3 percent reduces the extinction time to less than 300 years.
The trouble with this theory is that a host of large mammals, in addition to proboscidians, died off about this time. Giant ground sloths, giant beavers, giant bison, saber-toothed cats and many others also disappeared. Of these, evidence showed, only the mammoths and beavers were hunted by humans.
Moreover, hunting technology has not been notably successful at killing off species in any era.
"I think there is extremely little evidence of people being very good at killing off anything. That isn't to say that they haven't caused a lot of grief," said Ross MacPhee, chairman and curator of the Department of Mammology at New York's American Museum of Natural History.
Mr. MacPhee pointed out that the technological hunting prowess of the world was directed at fur seals and whales until the middle of the 20th century, yet no whale and only one seal species the Caribbean monk seal has been driven to extinction. Although their numbers have been depleted severely in many cases, the species themselves persist.
In South America, Mr. MacPhee said, humans arrived earlier than in North America. A different species of proboscidian, gonthospheres, was there, and the evidence of human hunting of them was "trivial," he said. Yet the Pleistocene extinctions in South America were even more severe than those in North America.
Mr. MacPhee proposes that perhaps the large mammals of the Pleistocene were ravaged by "hyperdiseases" severe bacteria or viruses such as the Ebola that killed rapidly. However, he has not been able to collect evidence to support this, in part, perhaps, because this kind of material is hard to recover.
"We've been defeated on several fronts," he said. He investigated some finds in northern Asia, but "the proteins that we needed to do the kind of investigations we were after were just in terrible shape. We couldn't identify pathogens."
The implication that perhaps humans were not responsible for the death of the Pleistocene megafauna might be good news for modern biodiversity. If it is hard to kill off a species with human technology, there may be hope that care and judgment can support the great chain of being.
This is ecologically important to us, and it makes for a good mystery to solve.

LOAD COMMENTS ()

 

Click to Read More

Click to Hide