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So, what caused megafauna extinctions? The two primary suspects in this mystery are hominin hunters and climate change. After numerous rowdy fistfights at scholarly conferences, the overhunting theory has become the most widely accepted. Quite a few still believe climate change was a secondary factor, because the swings between hot eras and frosty ones could cause substantial shifts in a habitat’s vegetation. When tundra became forest, mammoths no longer lived in paradise. Their numbers likely declined, and their groups could have become more isolated.
When the climate warmed, hippos and monkeys migrated into Europe, joining the woodland rhinos, elephants, boars, and deer. Tundra became boreal forest, and the cold adapted critters no longer enjoyed optimal conditions. This could have weakened them, and made them more vulnerable to hungry hominin hunters.
Then, when temperatures dropped, ice sheets advanced again, and the good old days ended for the warmth loving critters. Woodlands were displaced by tundra and taiga — good habitat for lemmings, arctic foxes, reindeer, woolly mammoths, and woolly rhinos.
Peter Ungar discussed research in Greenland, where scientists bored deep into the thick 150,000 year old ice sheet. In the ice core samples, the annual layers of ice buildup contained details about climate trends. Patterns could remain stable for thousands of years, and then suddenly change. The emergence of agriculture and civilization only became possible with the arrival of the current, unusually long warming trend, which began about 11,600 years ago. It followed a 1,200 year stretch of intense cold. The transition from intense cold to the modern warm trend occurred during one lifetime. A lass who was born in an arid tundra would see the land transform into a young forest by the time her hair was gray.
Now, gaze at the globe on your desk. As Earth makes its annual joyride around the sun, its axis tips. When the northern hemisphere tips closer to the sun, it’s summer time. Six months later, summer begins in the southern hemisphere, and winter arrives up north. The regions close to the equator consistently receive the most solar energy throughout the year, so they are Earth’s warmest — the tropics. Both the North Pole and the South Pole get the least solar energy, so they are icy year-round.
On your globe, note that most dry land regions on the planet are north of the equator. Also, at the top of the world, the northern edges of North America, Europe, and Asia extend into the Arctic Circle. Consequently, the northern hemisphere has experienced a number of intense glaciation cycles.
The southern hemisphere has far less dry land, and far more ocean area. The surrounding oceans retain heat, and encourage a more moderate climate. In the southern hemisphere, the bottom edges of South America, Africa, and Australasia do not come close to the Antarctic Circle. For these reasons, glaciation events have been less extensive.
The Last Glacial Maximum (LGM) was the frigid peak of the most recent glacial cycle. Ice sheets began growing about 33,000 years ago. Glaciation peaked between 26,500 and 19,000 years ago. Large regions of northern Europe, Asia, and North America were buried under ice sheets up to one mile (1.6 km) thick. During the LGM, climate conditions were similar across these northern regions. Glaciers retained so much frozen water that sea levels were 410 feet (125 m) lower than today. A lass could walk from Ireland to Scandinavia or France without getting her feet wet.
Bernardo Araujo’s team studied up-to-date climate models for the last 122,500 years. For 19 regions, they compared the dates when humans arrived, with the dates when megafauna species went extinct. They found that humans were entering Europe and Central Russia about 45,000 years ago. In the colonized regions of Eurasia, extinction dates began about 40,000 years ago, and continued until about 10,000 years ago — the longest of the megafauna extinction cycles outside of Africa.
Araujo emphasized that our colonization of Eurasia was a significant turning point in the human colonization of the planet. It was the first time that our fully tropical species was moving into regions that were colder than the conditions for which evolution had fine-tuned us. It was far more challenging for humans to survive in snow country.
Fernando Fernandez also found no connection between climate patterns and extinctions. He wrote that there were essentially two pulses of extinctions in Eurasia. The first pulse was from 45,000 to 20,000 years ago, across the southern latitudes. The second pulse was from 14,000 to 9,000 years ago, in the northern latitudes.
In North America, Fernandez reported a much quicker extinction spasm. It mostly occurred between 13,500 and 11,000 years ago. Experts still disagree when humans arrived on the continent, suggesting dates ranging from 20,000 to 13,000 years ago. By the time humans entered North America, they had developed effective tools and strategies for succeeding in snow country, making a faster dispersal possible. South American extinctions were mostly between 13,000 and 7,800 years ago.
Fernandez presented a list of arguments why climate change was not the primary cause of megafauna extinctions. Climate swings affected the whole planet, but the extinction spasms occurred at widely different times, in different places — not everywhere at the same time. The timing of extinctions does not closely correspond to the timing of glacial cycles. Preceding the megafauna extinction spasms were 31 earlier glacial cycles which wiped out few if any species.
Extinctions occurred first on continental mainlands, while species on isolated islands in the same region, with the same climate, survived much longer. When extinctions took place in a region, there is no evidence that plant species were zapped by temperature swings at the same time. It was the large animals that blinked out (the preferred game of hunters). Small animals did not vanish in the same era (like they might have during a climate shift). He did say that glacial cycles could have stressed ecosystems, making some species less resilient.
Baz Edmeades noted that most of Africa lies between the Tropic of Cancer and the Tropic of Capricorn, the equatorial belt. When there were extinction spasms in the equatorial belt, there was no rise of extinctions in regions where hominins had not yet arrived. The extinctions were limited to Africa and southern Asia — tropical regions where hominins resided.
OK! So, based on what I know today, I am convinced that climate change was not the primary cause of megafauna extinctions. I am also thoroughly convinced that the pattern of extinction spasms was closely related to the early emergence of advanced hominins in Africa, and to the later pattern of world colonization by humans.
I remain befuddled by one mystery. During the North America extinction spasm, most of the megafauna species that survived were not indigenous. They were immigrants from the Old World, like moose, bison, caribou, elk, deer, grizzly bears, black bears. Indigenous megafauna got hammered. Super-speedy pronghorn antelope were among the few to escape extinction. The implication here is that the Old World megafauna immigrants had arrived at about the same time as the Siberian hunters, and these foreigners were fully aware that humans were dangerous murderers — run! I was not able to find information confirming that “about the same time” is true.
William Stolzenberg presented a different twist. He shared a fascinating story about Joel Berger. Early in the twenty-first century, when Berger was working near the Teton Range of Wyoming, wolves from Yellowstone began wandering back into the region. They had been absent for 50 years, victims of a predator eradication project. For 50 years, moose and elk had not been bothered by serious predators. Berger freaked out. He tried scaring the moose with wolf calls and scents. No response. They had completely forgotten their natural fear of wolves. So, the wolves casually walked past the clueless moose mothers, and hauled away their calves. Eventually moose learned that wolves were dangerous.
Baz Edmeades grew up in South Africa, where he enjoyed observing the remnants of African megafauna at Kruger National Park. His deep interest in archaeology and evolution led him to read Björn Kurtén’s book on Pleistocene Europe. He was shocked to discover that 15,000 years ago, hyenas, leopards, and lions roamed Europe, and they closely resembled the animals he watched in Africa. Woolly rhinos and mammoths had cousins at Kruger. Not that long ago, large animals were incredibly abundant. Grassland regions of Europe were once a wildlife wonderland, like Africa’s Serengeti.
North and South America also had Serengeti-like grassland regions. Dan Flores wrote that the Great Plains used to be home to many species of large mammals, none of which had evolved adaptations for living near packs of aggressive bloodthirsty tropical primates with spears, dogs, and fire. Many blinked out. Five hundred years ago, when European colonists began arriving in great numbers, with highly advanced technology, life on the American Serengeti got blindsided with astonishing speed and efficiency.
Today, many documentaries and nature programs present images of the African megafauna that still survive in protected areas, like the Serengeti. These images of lions, zebras, giraffes, and baboons inspire astonishment among the wretched mobs trapped in sprawling, grungy, concrete landfills like New York City or London. But, compared to the Serengeti of 2 million years ago, the twenty-first century Serengeti is much diminished.
Two million years ago, all the other continents were also astonishing Serengetis. Earth was one big wonderful celebration of abundant life. The critters of every ecosystem had coevolved with each other, resulting in functional relationships between the eaters and the eaten. Loose cannon critters were not yet molesting the sacred dance. Today, of course, a hurricane of swarming tropical primates has reduced Planet Serengeti to Planet Train Wreck.
It’s heartbreaking to comprehend that this staggering tragedy was driven by the innocent unintended consequences of thousands of years of gradually accumulating more and more clever innovations. Today, the rate of extinctions is in the stratosphere. Innovation and technology have given us the ability to thoroughly obliterate healthy ecosystems faster than ever before. We call this “progress,” one of our god words. Another one is “growth.”
In North America, when humans arrived, there were at least nine species of big cats, and seven species of elephants. The biodiversity was incredible — beavers as big as bears, two-ton buffaloes, armadillos the size of VW Beetles
Mammoths emerged in South Africa about five million years ago. By 2.6 million years ago, they had spread across Eurasia and North America. Around 190,000 years ago, all mammoths in Europe had evolved the woolly look. Until 14,000 years ago, mammoth country ranged from Western Europe to Siberia to New England to Mexico. The last mammoths survived until about 3,700 years ago, on Wrangel Island, off the coast of Siberia.
Aurochs once ranged from England to Korea, and south to India and North Africa. Rhinos once ranged from Africa to Europe to Sumatra. Leopard country spanned from southern Africa to England, to Java. Short-faced hyenas were as big as lions, and their addresses included India, China, Transvaal, and Europe. And on and on….
Tim Flannery mentioned Neanderthals, who had significantly larger brains than humans. They were long-time residents of Eurasia that had coevolved with the other large animals. For hundreds of thousands of years, they coexisted with mammoths, straight-tusked woodland elephants, and two species of woodland rhinoceros. Scholars tend to regard Neanderthals as dullards. Ecological stability is not a sign of pathological intelligence.
Around 5 million years ago, the climate in Africa was getting cooler and dryer, forest area was being displaced by expanding savannah. The ancestors of hominins learned ways to survive in the changing conditions. Our hominin ancestors were bipedal at least 3.6 million years ago. Somewhere around 2.5 million years ago, the climate in Africa once again entered a cooler and dryer pattern.
By this time, our hominin ancestors were getting better adapted to savannah living. They were bigger and smarter, using stone tools. They may have been cooking with domesticated fire, but we’ll never know when the first fire was kindled. As previously mentioned, hominin evolution was influenced by having the ability to regularly dine on cooked food, which significantly tweaked the design of our teeth and digestive tracts. This implies that domesticated fire appeared early in the game.
The series of megafauna extinctions that occurred during the hominin era began in Mother Africa. Lars Werdelin, an expert on ancient carnivores, wrote that beginning around 2 million years ago, large carnivore species began to gradually decline. Hominins were becoming regular hunters, and they were eating more meat. Carnivore extinctions accelerated around 1.5 million years ago. Coincidentally, Homo erectus emerged around 1.5 million years ago. Erectus was the first advanced hominin, having a brain larger than average for its body size. This era corresponds to the oldest known evidence of domesticated fire. Today, only two percent of the original African large carnivore species still survive.
Werdelin assumed that hominins were not deliberately hunting large carnivores, which would have been insanely dangerous. The extinctions were likely due to a decline in herbivores — the prey that carnivores depended on. Was climate change reducing the forage that herbivores required for survival? Small carnivores were not in decline, which would have been the case if ecosystems were being walloped by a climate shift. Werdelin believes that hominins had become successful competitors for the traditional carnivores, both of whom were eager to dine on the same prey.
Baz Edmeades noted that the African continent was loaded with megafauna 1.8 million years ago, but many were gone by 1.4 million years ago. In the good old days, Africa had nine species of big cats (three today), up to nine species of elephants (one today), and at least four types of hippos (one today). There were giant antelopes, giant hyenas, giant pigs, giant monkeys, giant baboons, and many others — all gone. Over the course of many thousands of years, the consequences of hunting just a bit too hard accumulated.
Some species that disappeared in Africa continued to survive on other continents. Edmeades emphasized that during the African wave of extinctions, there were no corresponding extinction blips in Siberia, Europe, Australia, or the Americas. In these other regions, most megafauna species thrived for another million years. A jury would not convict climate change for the extinctions in Africa.