[Note: This is the nineteenth sample from my rough draft of a
far from finished new book, Wild, Free, & Happy. I don’t plan on reviewing more books for a
while. My blog is home to reviews of 201
books, and you are very welcome to explore them. The Search field on the right side will find
words in the full contents of all rants and reviews, if you are interested in
specific authors, titles, or subjects.]
Climate
Shifts?
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.
Global
Serengeti
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.
Mother
Africa
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.
