The mysteries of extinction are so many and so baffling that it is small wonder no book in English has been written on the subject. Since 1906, when Henry Fairfield Osborn summed the matter up in his paper of fifty-odd pages, “The Causes of Extinction of Mammalia,” Eiseley credits only two theories with contributing anything new to the discussion.
One is the hypothesis of Sewall Wright and his co-workers that when an animal was greatly reduced in numbers it would suffer fatally from inbreeding.[25] This, however, leaves us still searching for what reduced its numbers so radically.
The other theory is Sauer’s: Man, the hunter, destroyed the larger, clumsier, and more gregarious animals largely by means of fire drives, and these fires made the grasslands.[26] Or, at least, the fire drives “broke the back” of mammalian resistance.[27] Eiseley objects on a number of grounds. It was not alone the large, clumsy, and gregarious animals that disappeared. Certain mollusks, a variety of toad, a subfamily of rabbits, the dire wolf, the saber-toothed tiger, three forms of antelope, the short-faced bear, and a small horse also disappeared. More damaging still to Sauer’s theory is the fact that a number of birds became extinct. Eiseley asks, “Why, if this method was so deadly, did the living bison and the living antelope roam the plains in countless numbers?” He points out that, while there is abundant evidence of extinct bison caught and killed in fire drives, there is no proof of mass kills of mammoth, horse, camel, and antelope.[28] He also mentions the mastodon, the giant beaver, and the sloth, which frequented eastern forests or northern bogs and died in them. “Though man was on the scene at the final perishing, his was not ... the appetite nor the capacity for such gigantic slaughter.”[29] Though Sauer believes that the numbers of hunting man in the New World were comparatively large when he killed Bison antiquus, most authorities disagree. Alfred S. Romer believes that if man had been numerous enough and deadly enough to play a major part in the killing, we should find more evidences of his association with the extinct mammals.[30]
Romer and Edwin H. Colbert have put forward another explanation for the extinction of the mammals. They suggest that the advent of man in the New World may have upset a nicely balanced state of nature.[31] But man had been living with just such animals in the Old World for hundreds of thousands of years before they became extinct. What, then, destroyed the mammoth in Europe?
The most pulling of all the fossils of extinct animals are those in the deep Alaska muck beds. Their numbers are appalling. They lie frozen in tangled masses, interspersed with uprooted trees. They seem to have been torn apart and dismembered and then consolidated under catastrophic conditions. Eden and Plainview spear points and perhaps one Clovis have been found in these chill beds. Skin, ligament, hair, flesh, can still be seen.[32] If scientists can solve this mystery before the high-pressure water stream of the miner disperses the evidence, perhaps we shall be nearer solving one of the greatest and most tantalizing problems involved in the story of early man—the date of the extinction of the great mammals.
This problem of when the mammoth died should have puzzled the Old World as well as the New and caused us to question the dating of Neanderthal and Cro-Magnon quite as much as Folsom man. Oddly enough, it did nothing of the kind. In Europe the mammoth was accepted as diagnostic of the glacial period. The fact that a Magdalenian man of southern France sketched a mammoth on the wall of a cave proved that the man existed in the Great Ice Age. But in America, if a spear point turned up with the bones of a mammoth, too many anthropologists accepted it as proof that the animal died after the ice fields had melted. The mammoth proved the antiquity of man in Europe; man proved the modernity of the mammoth in America. The only shred of evidence to support such reasoning was the questionable pottery and coal that lay beside the mastodon bones in Ecuador. We should have had more and better proof, and we are beginning to get it.
More Radiocarbon Dates for Extinct Mammals
Working together, archaeologists, paleontologists, and physicists are providing more and more facts about the great extinction. Archaeologists are supplying artifacts for cultural associations, and animal bones that the paleontologists identify. In radiocarbon laboratories, the physicists are dating the bones and sometimes charcoal from man-made fires. Through the evergrowing list of dates, many early theories are being replaced with factual knowledge. Some of the dates, however, must be taken with a grain of sodium chloride. A single date from a single sample in only one locality is not too trustworthy. The hazards are obvious, yet nevertheless we have a fairly large body of facts. From these, a general impression of the great extinction is beginning to take shape. As anticipated, man and climate are involved in the disappearance of the animals.
As for climate, a period of much warmer temperatures followed the end of the last glaciation. This lasted from about 10,000 to 2,600 years ago. Antevs isolates the time of highest heat—the Altithermal—as about 7,000 to 4,000 years ago.[33] This matches fairly closely the last dates for our extinct mammals. Heat and aridity may have driven the larger animals to the more and more limited watercourses where man himself would concentrate. Paul S. Martin has noted that the first large mammals to disappear were those in Alaska and Mexico, and that they were followed by the animals of the Plains toward what must have been the beginning of the hot and dry Altithermal period. Martin believes that the grazing and browsing mammals found refuge in the savannas of Florida.[34]
Working with more than 100 radiocarbon dates concerned with the great extinction, Jim Hester (no relation of the junior writer) has brought together results published through 1959.[35] He provides the first reasonably clear picture of the sequence and magnitude of lethal events. We see the ancient forms of horse, camel, and bison, as well as the dire wolf and Columbian mammoth, beginning to disappear 8,000 years ago. Bison antiquus lingers later, though Clovis mammoth hunters may have been active in the Southwest at the same time that Folsom bison hunters were busy on the Plains. Hester’s summary shows how concerned man was in the final death of the great mammals. He lists the last dates for 27 of them. Nine—one-third—were found in archaeological sites of early man; some others were dated by charcoal that may have come from fires where he cooked the meat of the great beasts.