Deadly Voyager

by James Lawrence Powell

  MONTE VERDE

  When biologist J. B. S. Haldane was asked what it would take to falsify Darwinian evolution, he is said to have answered, “Fossil rabbits in the Precambrian.” In the same vein, if we ask what would falsify Clovis First, the answer would be, “An archeological site reliably and distinctly older than the oldest Clovis site known.” The crux is the word “reliably.” As we have seen, when the radiocarbon method first appeared it turned out to offer many more opportunities for error than anyone had imagined, so that at least for a time, defenders of Clovis First could always question the accuracy of putative pre-Clovis dates and insist on more and better ones. And they got what they had wished for.

  The first site to offer the promise of being reliably older than Clovis was discovered in 1975. It was located not near any previously known Clovis site in North America, but down the coast of Chile at 41°S, 13,000 km (8,000 mi) close to Pilauco but far from the one-time Beringia. Two years later, Tom Dillehay, an American then working at a Chilean university and now a professor at Vanderbilt University, began to excavate there. Monte Verde was that rare archeological site located in the open air and exceptionally well preserved due to being in a peat bog that retarded the action of bacteria.

  The first radiocarbon dates on bones and charcoal from the upper of two layers at Monte Verde arrived in 1982 and gave an age of about 14,800 years ago, more than a millennium older than the oldest known Clovis site. In 2008, Dillehay et al. reported that seaweed evidently eaten by the Monte Verde people dated to 14,220 to 13,980 years ago. Then in 2015, he and co-authors reported dates on the lower layers of “at least about 18,500 and 14,500 [years ago].”

  The Monte Verde story proved as controversial as any in science, with one critic calling the research “chaotic,” “inconsistent,” and “confusing.” But Monte Verde was only the first of many pre-Clovis sites that scientists would discover and date. Here are three other examples:

  • Below a Clovis layer at Cactus Hill, Virginia, scientists found artifacts that dated from 15,070 ± 70 to 16,940 ± 50 years ago. (Its location on the Atlantic Coast and its age have been cited as support for the Solutrean hypothesis.)

  • The Topper site in South Carolina, which has been a primary focus in the evaluation of the YDIH, also has artifacts below the Clovis stratum. They date to about 16,000 years ago.

  • The Buttermilk Creek Complex in Texas lies beneath Clovis artifacts and dates to between ~13,200 and 15,500 years ago. Its investigators write that it “confirms the emerging view that people occupied the Americas before Clovis and provides a large artifact assemblage to explore Clovis origins.”

  If we take a rough average of the oldest pre-Clovis finds, say about 16,000 years ago, and compare them to the end of Clovis, they differ by about 3,000 years. And the sites that have been found and dated can hardly be the oldest. Indeed, recent DNA analysis suggests that the first to arrive in North America may have done so 20,000 years ago or even earlier.

  The point for us is that people occupied much of the Western Hemisphere for thousands of years before Clovis and the YD. During those millennia, they survived all the extreme climatic events that Nature could throw at them, managed to feed themselves, been able to spread from Beringia to Tierra del Fuego, and even had time to create what we can only call art. The change of temperature with the YDB would have been uncomfortable but not fatal, no worse than going from summer to winter, or, say, moving from Ft. Lauderdale to Cleveland.

  ARCHEOLOGICAL EVIDENCE

  We know that the Clovis toolkit disappeared with the YD, but what about the people themselves? They did not go extinct, but can we detect a decline in their population consistent with the YDIH? In the absence of Clovis bones, which we know are rare, the only evidence must come from proxies. In 2011, archeologists David Anderson and Albert Goodyear, together with original YDIH authors James Kennett and Allen West, reported on three such stand-ins for post-Clovis population.

  Their first strategy was to count the frequency of spear and arrow points before and after the YDB. This depends on the reasonable assumption that the fewer people there were, the fewer the stone artifacts they would have left behind. For their data, Anderson et al. used the Paleoindian Database of the Americas, which includes information, ages, and images for more than 10,000 stone points from across the Western Hemisphere. (Open databases for other countries or regions bring the total number of radiocarbon dates on these objects to an astounding 70,000.) They found a large drop in the number of projectile points after Clovis, followed by a rebound.

  Next they gauged population by examining the artifacts from several well-studied Clovis quarry sites, estimating their usage before and after the YD. They found heavy use of the quarries by the Clovis people, and close to zero post-Clovis.

  Their third method, Summed Probability Analysis, also relies on overall numbers, in this case, of radiocarbon dates. In 1987, Stanford archeologist John Rick proposed using “dates as data,” suggesting that the raw number of radiocarbon dates over time is related to the total number of person-years of human existence in a given area and thus can serve as a proxy for human population and patterns of occupation. As a test, Rick used the record of dates from preceramic Peru to show that highland and coastal areas had different histories of occupation. The method worked. Anderson et al. used dates as data 20 years later, when vastly more, and more precise, radiocarbon dates had become available. They found that the change at the onset of the YD had been rapid and in some areas may have caused population declines of as much as 30-50%, with population rising again in the following centuries.

  Climate change as the cause of Clovis decline cannot explain these results, but the YDIH can. This does not prove the hypothesis, but is consistent with it. The least one can say is that these results might have tended to falsify the YDIH, but did not. Now let us turn to the extinction of the big mammals that accompanied the YD.

  17

  GREAT MONSTERS

  DARWIN

  As Charles Darwin began to convert his shipboard notes into The Voyage of the Beagle, his mind turned to extinction and in particular to the fossils of animals no longer found on Earth. He devoted the final pages of Chapter VIII to “Fossil gigantic Animal — Types of Organization constant — Change in the Zoology of America — Causes of Extinction.”

  Darwin knew something of South American fossils even before his voyage, thanks to a collection of 32 extinct genera that had been found in a Brazilian cave and shipped back to Europe for display. He saw many more in his explorations in South America. That extinction was a fact had been established only two decades earlier by George Cuvier, who proposed that catastrophic floods had repeatedly wiped clean the slate of life. We might name Cuvier the “Father of Catastrophism,” the geological theory that ran counter to Lyell’s uniformitarianism and gave rise to a long-lasting debate.

  In a few words, Darwin showed that this background and his own observations in South America sufficed to lead him to a great insight: “The extinct species are much more numerous than those now living.” This, he said, would “hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.” And indeed it did. For extinct animals to greatly outnumber living ones means that a process must exist to preserve some species while exterminating most others. This indeed must have happened repeatedly and taken a great deal of time. In Darwin’s few words we see the kernels of natural selection and deep time. Here was genius.

  Darwin realized that many of the “great monsters” that had “swarmed” the South America continent had vanished only recently in geologic time. This naturally caused him to wonder, “What, then, has exterminated so many species and whole genera?” His first thought, following Cuvier, was “some great catastrophe,” though of course Darwin did not envision meteorite impact, which had not yet been conceived. But such a cataclysm would have required “shak[ing] the entire framework of the globe, from Southern Patagonia to Behr
ing’s Strait,” something of which no known process was capable. Following Lyell, Darwin preferred “slow and gradual changes.” He speculated about one possibility, a “change of temperature,” but doubted it would have been able to destroy “at about the same time...the inhabitants of tropical, temperate, and arctic latitudes on both sides of the globe.” Finally, he wondered whether “man, after his first inroad into South America, destroy[ed], as has been suggested, the unwieldy Megatherium and the other Edentata?” He thought this too was doubtful, for why would man also have driven to extinction “the little tucutuco at Bahia Blanca, and the many fossil mice and other small quadrupeds in Brazil?” Darwin wrestled with the same three causes of megafaunal extinction that still confound scientists today: [extraterrestrial] catastrophe, climate change, and overkill.

  Earlier we referred to the history of three great controversies of twentieth century earth science: meteorite cratering, anthropogenic global warming, and continental drift. Each theory appeared in the last decade of the nineteenth century or the first decade of the twentieth, then took 50-60 years to find acceptance. The debate over the cause of the great end-Pleistocene mammal extinction began in the 1830s with Darwin and is still going strong today, making it a contender for the longest scientific controversy still extant. There could be no better example of how difficult it is to solve problems in the historical sciences like archeology and geology, where events may have left little or no trace, continually confronting scientists with the frustrating “absence of evidence.”

  One coming to the megafaunal extinction debate from another field is first surprised to discover how long it has been going on, second overwhelmed by the vast literature on the subject, and third shocked by the vituperation the controversy has engendered, enough to shake even someone familiar with the disputes over continental drift and the Alvarez Theory.

  Of the two main theories for the extinction of the megafauna from Darwin’s day onward, overkill has been the most contentious. The hypothesis fit neatly into the Clovis First theory, in which Paleo-Indians crossing Beringia and migrating down the ice-free corridor encountered “naive” species who had never met human hunters, slaughtering the hapless creatures into extinction. Many trace the full exposition of the overkill hypothesis to the 1960s writings of Paul Martin of the University of Arizona. In the face of fierce opposition, he continued to defend his thesis until his death in 2010.

  As examples of the passions aroused by the overkill hypothesis, let us consider two articles from this century. In 2003, Donald Grayson and David Meltzer wrote, “A Requiem for North American Overkill.” (Both authors would later criticize the YDIH in several articles.) It is hard to call their article anything but a blistering, ad hominem attack on Martin. “In North America,” they write, “archaeologists and paleontologists whose work focuses on the late Pleistocene routinely reject Martin’s position for two prime reasons: there is virtually no evidence that supports it, and there is a remarkably broad set of evidence that strongly suggests that it is wrong.” They accuse Martin of “turning the absence of empirical support into support for his beliefs, removing the overkill hypothesis from the realm of science and plac[ing] it squarely in the realm of faith.” This is a contender for the greatest of insults one scientist can hurl at another, though “pathological pseudoscience” is a close rival.

  But a year later, in an article titled, “A Premature Burial,” Stuart Fiedel and Vance Haynes turned the tables on Grayson and Meltzer by accusing them of “numerous mistakes [and] mere theatrical posturing.”

  The Grayson-Meltzer article is the second we have met to use “Requiem” in its title. Do these obituaries have any practical effect besides angering a theory’s proponents? If the authors of such articles have made a strong case, research on the topic should naturally dwindle as busy scientists, some seeking tenure with no time to waste, vote with their feet against it. But with both the YDIH and overkill, just the opposite has happened. The number of articles on each topic has increased, some of them written by the very persons who wrote their Requiem, as though a doctor had continued to treat a deceased patient.

  Though both overkill and climate change as the cause of the YD mammal extinction continue to have many supporters, both have a long set of problems:

  OBJECTIONS TO OVERKILL AS THE CAUSE OF THE MEGAFAUNA EXTINCTION

  • The only three extinct megafauna for which there is direct evidence of hunting are the mammoths, mastodons, and gomphotheres. The bones of Pleistocene camel and horse occur in great abundance, but there is no evidence that Paleo-Indians hunted these readily available animals. Yet many cultures have shown a great fondness for horse meat, and some still do.

  • Scientists have discovered only 14 “kill-sites,” where human and megafaunal bones occur in place together. None contain the bones of camel or horse.

  • Many Pleistocene megafauna in Europe and Asia went extinct at about the same time as in North America, even though these animals had a much longer exposure to human hunters. In Siberia and other parts of northern Eurasia, humans and large animals had coexisted for ~125,000 years. These megafauna had long known human hunters and were by no means “naive.” Many megafaunal extinctions took place in northern Siberia along the Arctic Ocean at about YDB time. But among the hundreds of sites with megafaunal remains along the 5,000-km-long (3000 mi) Siberian coast, scientists have found only one human campsite.

  • How could the Clovis people have hunted species to extinction when their culture lasted only several hundred years and when their population evidently went into dramatic decline at the same time? In other words, could human hunters over-hunt the very prey on which their lives depended? In this macabre race to oblivion, which would be the first to succumb? The animals were innumerable; the Clovis vanishingly few by comparison.

  • In the great Pleistocene dying, all the many horse species in North America went extinct at once, as did all six species in South America. But genera and species do not die; they are constructs of our minds. Individuals — single living creatures — die. Prior to the YD, spread across the Western Hemisphere from Alaska to Tierra del Fuego, in many different environmental niches, lived countless millions of horses molded by tens of millions of years of evolution. Is there any reason to believe that they would have been fewer in number than the scores of millions of bison that experts estimate once existed? To exterminate all 23 species of Equus in the Western Hemisphere required not only that millions of individuals died, but that each species had its numbers decimated to the point where too few breeding pairs were left to keep the species alive. Is that conceivable?

  • No horseman or horsewoman can be persuaded that human hunters, on foot and armed with primitive weapons with an effective range measured in feet, could have hunted a myriad of wild horses to extinction. As anyone knows who has tried to approach a wild horse on foot or to catch a domesticated one that decides not to be caught, these animals have a mind of their own and get up to full speed in seconds, then maintain their speed for miles. Once their flight instinct takes over, they are almost instantly beyond the reach of arrow or spear and then out of sight. Today, about 80,000 horses live in the wild in the Western U.S., descendants of those brought by the Spanish in the 1500s. They reproduce so rapidly that they have become a major problem, pitting animal lovers against their otherwise natural allies, environmentalists, with politicians caught in the middle. Attempts to round them up using motorized vehicles having failed, the Bureau of Land Management has had to resort to “Judas” horses and helicopters. Anyone who today suggested rounding up wild horses on foot would be laughed out of the room. The pre-Clovis and Clovis people had no domesticated horses, only their moccasined feet for the chase and their primitive weapons. To those who know horses, overkill makes no sense.

  OBJECTIONS TO CLIMATE CHANGE AS THE CAUSE OF THE MEGAFAUNA EXTINCTION

  If overkill remains in doubt as the explanation of the megafaunal extinction, what about the other alternative, climate change? We have a
lready found it questionable for the Clovis decline. Here are some of the objections to climate change as the cause of the megafaunal extinction:

  • During the Pleistocene, but before the YD, many abrupt changes of climate occurred. Yet the megafauna that went extinct with the YD had survived them all. The horse had survived in North America for the 50 million years since the Eocene.

  • The YD megafaunal extinction was a highly anomalous, one might almost say, unnatural event. By one account, the extinction was harder on large animals than any extinction event in the last 65 million years.

  • The YD began and ended suddenly, far faster than typical climate change.

  • In North America, the YD brought the return of glacial temperatures. But the animals that then went extinct had just survived scores of thousands of years of even more extreme glacial climates in the last Ice Age. Would a drop of several degrees, less than the change from summer to winter, have been enough to destroy entire genera across an entire continent?

  • Animals of the tropics also went extinct, yet there the climate barely changed.

  • During the YD, as noted in our discussion of the Pilauco site, the climate of the two hemispheres at mid- and high-latitudes changed in the opposite direction: as the Northern Hemisphere turned colder, the Southern Hemisphere turned warmer. If climate change explains the megafaunal extinction in one hemisphere, it cannot explain it in the other.