Doug Peacock, the grizzly bear expert, lives near the Yellowstone River in Montana. In 1968, the largest collection of Clovis artifacts was found not far from his home, on the Anzick ranch. The Clovis culture of Native Americans existed for about 300 years, from 13,100 to 12,800 to years ago — during the era of megafauna extinctions. Of the 35 genera of large mammals that went extinct in America, half of them vanished in a 500-year period, from 13,200 to 12,700 years ago.
The Clovis culture developed a new and improved design for the flaked stone points used as spearheads. The long broad sharp points made it much easier to kill large animals, like mammoths and mastodons. Amazingly, this new technology spread to every corner of North America within just 200 years. Clovis points are sometimes found close to the remains of extinct animals. Clovis technology appeared suddenly, and vanished suddenly.
Today, the waters of the Bering Strait separate Siberia from Alaska. During ice ages, sea levels dropped, and the strait became dry land, called Beringia. Around 20,000 years ago, the last era of glaciation peaked. The glaciers made it impossible to travel from Beringia to warmer regions in the south. Few, if any, humans migrated into America prior to 15,000 years ago.
About 14,700 years ago, the climate changed when the Bøling-Allerød warming period began. At that time, sea levels were 450 feet (137 m) lower than today. During the warm period, thawing opened up a corridor to the south, vegetation recovered, and by 13,100 years ago, it became possible to migrate from Beringia to Alberta and northern Montana.
The human immigrants from Siberia did not live at the top of the food chain. They often had lunch dates with hungry sabertooth cats, lions, dire wolves, American cheetahs, grizzlies, and short-faced bears. Short-faced bears weighed a ton, and when they stood on their hind legs, were 15 feet tall (4.5 m). Maybe Clovis points were invented to reduce losses to predators. Better weapons also made it easier to hunt large animals.
After 1492, the early European explorers were astounded by the incredible abundance of wildlife in the Americas, compared to the battered ecosystems back home. But what they saw in America was actually a biosphere that was missing many important pieces. The zenith of American wildlife was prior to 13,000 years ago.
So, the Clovis period began, existed for 300 years, and vanished. It ended when the frigid Younger Dryas period began, 12,800 years ago. The Younger Dryas lasted 1,300 years. When warmer times returned, some clever people began fooling around with plant and animal domestication, which blew the lid off Pandora’s Box. We’re still living in this warm phase, an unusually long period of climate stability. We’re long overdue for another ice age, but industrial civilization has seriously botched the planet’s atmosphere, and we’re sliding sideways into an era of ecological helter-skelter.
There are four theories about the megafauna extinctions, and this subject is the source of decades of loud shouting and hair-pulling. One theory asserts that a comet or asteroid strike filled the atmosphere with dust, causing a very long winter. Where’s the crater? There is none, because the impact hit a glacier. Why did the short-faced bears vanish, but not the other bears? How did moose, bison, elk, and humans manage to survive?
The disease theory notes that some viral pathogens, like influenza or cowpox, are sometimes able to transfer from one species to another. Maybe species that migrated from Asia smuggled in some virulent viruses. But species-to-species transfers are more likely to happen in confined conditions, like barnyards and livestock herds. During the extinctions, a variety of browsers, grazers, and carnivores disappeared, from an entire continent, in a short stretch of time.
The climate change theory notes that when the Younger Dryas blast freezer moved in 12,800 years ago, the Clovis culture suddenly vanished. Eventually, “nearly every animal over 220 pounds (100 kg) died off and only animals weighing less than that survived this extinction. A notable exception was the grizzly, along with modern bison, moose, elk, caribou, musk ox, polar bear, and chunky humans.” Why hadn’t numerous earlier ice ages caused similar mass extinctions?
Paul Martin was the father of the Pleistocene overkill theory, which asserts, that man, and man alone, was responsible for the unique wave of Late Pleistocene extinctions. He believed that the American extinctions occurred rapidly, in a “blitzkrieg” of overhunting. He argued that across many thousands of years, extinction events corresponded to human colonization — in Australia, the Americas, Tasmania, New Zealand, the Caribbean, and so on.
Hunting clearly played a role, but it’s hard to believe that all of the horses and wolves in America were driven to extinction by hunters with spears. Blitzkrieg seems like too strong a word. Unlike mice and bunnies, large mammals have low rates of reproduction. “If hunters remove just 4 or 5 percent of a population of slow-reproducing wildlife, those animals are on a road headed toward extinction.” The megafauna extinctions could have occurred gradually, over decades and generations, too slowly to raise alarm.
Climate shifts can spur extinctions. The hills near Peacock’s home are red, because pine beetles are killing the whitebark pines. The beetles are thriving because warmer winters enable more to survive. For grizzlies, pine nuts are a dietary staple. He worries that the bears might be driven to extinction by tiny beetles that benefit from the emissions of consumer society.
Let’s zoom back to the Clovis site discovered near Peacock’s home in 1968. He didn’t learn about the site until the mid-1990s. Scientists had hauled away a bunch of artifacts, but didn’t return to perform a thorough excavation. Peacock was able to encourage additional work at the site, which began in 1999. This inspired a years-long adventure in learning, which eventually resulted in a book, In the Shadow of the Sabertooth.
The Anzick site was the richest discovery of Clovis artifacts. Among the findings was the skeleton of a boy, about 18 months old, the only remains of a Clovis human ever found. It is also the oldest human skeleton found in the Americas. The results of DNA sequencing were published in 2014. “The Montana Clovis people are direct ancestors to some 80 percent of all Native North and South Americans living today.” This line came from Northeastern Asia. The boy’s genes strongly resemble those of a 24,000 year old skeleton from Lake Baikal in Central Siberia.
“The one unmistakable lesson of the Late Pleistocene extinction is that human activity combined with global warming is a potential, ageless, deadly blueprint for ecological disaster.” Today, the disaster we’re creating will be of far greater magnitude, and technology will not be able to rescue us. It’s time to rise up and defend this planet.
For readers who have a comprehensive working knowledge of paleontology, this book might be easy to understand. It summarizes the highlights of decades of scholarly research, and comments on the major controversies. General readers (like me) are more likely to struggle with the non-linear presentation. Be sure to look at the revised edition (2014), not the first edition (2013). The first edition was printed before Peacock could review, correct, and polish the manuscript, due to a health crisis — and the text was a mess. The Kindle version is the first edition.