Megafauna are animal species that can grow to weigh more than
100 pounds (44 kg). Our hominin
ancestors emerged in Mother Africa maybe four million years ago. They walked upright on two legs, and
eventually learned how to kindle fire, and hunt large game. These ancestors have been suspected of
influencing the extinctions of some African megafauna that occurred between about
2.5 and 1.4 million years ago.
Much later, after Homo
sapiens emerged, many more species of megafauna disappeared. These extinctions happened on the five
continents outside of Africa, mostly between 50,000 and 12,000 years ago. The term “megafauna extinction” usually
refers to this era, when humans were colonizing the planet, and feasting on
large herbivores. Questions about the
cause of these extinctions have inspired many theories, more than a little screechy
controversy, and a few bloody noses.
End
of the Megafauna is the latest book on this subject. It was written by Ross MacPhee, a scientist
at the American Museum of Natural History in New York. It helpfully updates the discussion with the
findings of recent research. It is also extremely
careful not to present a firm conclusion about the cause of the extinctions,
for the simple reason that absolute certainty is impossible — almost all of the
puzzle pieces will never be found. Every
theory contains an uneven mix of strengths and weaknesses. The two theories that are taken most
seriously are climate change and human impacts.
Today, few believe that climate change could have been the
sole cause. The one exception is the
extinctions in Sahul, the landmass of Australia, New Guinea, and Tasmania, when
they were joined together by low sea levels.
In Sahul, evidence of early human activities is quite scarce. Elsewhere, climate change theories are now
getting less and less support.
Charts of global climate trends during the Pleistocene are a lively
zigzag of sharp spikes and dives. The
lineages of most megafauna species extend back millions of years, and most of
them managed to survive through numerous big swings. But, the actual timing of megafauna
extinction spasms rarely corresponds with climate transitions. Climate certainly impacted regional
ecosystems — woolly mammoths were not delighted when tundra was displaced by annoying
forests. Nor were herds on the Sahara,
when lush grasslands withered into scorching desert.
The arguments for human hunting are far more compelling. As the human diaspora migrated out of Africa,
and colonized one continent after another, extinctions repeatedly followed
their arrival. Hey! This is important! Extinction spasms did not precede human
colonization, and there is no controversy about this. While megafauna extinctions shadowed the arrival
of humans in the U.S. and Canada, the nearby Caribbean islands were unaffected
— until humans first set foot on them several thousand years later. Islands around the world were the last
regions to get zapped.
A primary voice in the hunting discussion was Paul Martin, who
first published his overkill hypothesis in 1966. Working at sites in North America, and using
the latest specimen dating technology, he concluded that most of the
extinctions there took place during a thousand year period, following the first
arrival of humans from Siberia. At least
50 species of large animals vanished — horses, camels, mammoths, and so on.
During this same thousand year period, humans also colonized
all of South America, where the megafauna got hammered even harder. In Martin’s vision, as the colonists spread
across the New World, they routinely ran into animals that had never before
seen a human, and therefore had no fear of them. The naïve critters were easy to kill, and
delicious to devour. Before they could
figure out that humans were deadly dangerous, they were roasting over the fire. Hunting bands lived well, ate well, grew in
number, and expanded into new regions.
It takes a lot of imagination to explain how so many species,
over so vast an area, disappeared so quickly, when everything was roadless
wilderness, and primitive humans were few in number. Martin envisioned the thousand year process
in the Americas as something like a blitzkrieg (lightning war) of
overkill. Hunters spread out from Alaska
to the bottom of South America, rushing forward like a bloody tsunami wave,
killing all they could, and leaving little behind — fanatical annihilation. Do you find that a bit hard to believe? I do.
With regard to the possibility of overhunting, MacPhee
expresses doubts about some aspects of Martin’s hypothesis. Martin wasn’t the first to propose
overhunting, he joined many others, but his views were the most extreme. In the book, the less extreme views get
little mention.
Obviously, from an evolutionary timeframe, the New World
spasm of extinctions was lightning fast.
But, from a human timeframe, a thousand years can seem like quite a
while. I expect that at least a few of
my readers are younger than 200. A much
earlier extinction spasm in Africa took place over hundreds of thousands of
years, when our ancestors were fewer in number, had smaller bodies and brains,
and still had much to learn about the art of hunting.
Killing megafauna just slightly in excess of their fertility
rate could wipe them out over the passage of centuries. It wasn’t so much about the intensity of the
hunting as the fragility of the hunted.
Over a thousand years, and many generations of hunters, the process of extinction
may have been essentially imperceptible.
Scarcity increased at a gradual pace.
Elizabeth
Kolbert noted that modern elephants do not reach sexual maturity until
their late teens, each pregnancy takes 22 months, and there are never
twins. Because they reproduce so slowly,
mammoths could have been driven to extinction by nothing more than modest
levels of hunting. Peter
Ward estimated that if hunters had regularly killed just two percent of the
mammoths each year, the extinction process would have taken 400 years — too
slow for multiple generations of hunters to notice.
MacPhee noted that he often jabbers with other scientists
about the extinctions. He has found that
the majority believe that humans played a major role, but not all agree that
our role was exclusive. Out of
curiosity, I read several reviews of his book that were written by other
readers, and was surprised to see that some of them, with great relief,
believed that the book’s message was that humans had been found innocent. It seems that in the desire to appear
completely impartial, clear factual statements about the elephant in the room seem
to have gotten diluted enough to be confusing.
If we believe that the ancestors of environmentally conscious
Native Americans (or anyone else’s wild ancestors) were responsible for causing
extinctions, it’s tempting to presume that the human species must be inherently
flawed. Therefore, there is no urgent need
to care about anything. To avoid this,
educators, and other concerned adults, seem to have a tendency to deliberately
downplay or deny the darkness of reality, because if kids (or anyone else)
comprehend the truth, intense despair will reduce them to walking dead zombies. But, if we sweep reality under the bed, their
hope will survive, and they can fully devote their lives to a heroic adventure
in mindless, planet-thrashing Sustainable Growth™. As they say, we live in interesting times.
Overall, MacPhee wrote a fine book. I had just two issues. (1) The discussion of human hunting was
limited to Martin. Other non-blitzkrieg,
imperceptible overkill viewpoints were not included. (2) If some readers concluded that humans
were innocent, then maybe some important facts were not stated with sufficient
emphasis. Megafauna extinction is a
prickly subject.
I very much appreciated the numerous illustrations by Peter
Schouten. His megafauna portraits add a
powerful dimension to the reader experience.
Schouten’s illustrations portray megafauna living in their ecosystems. They seem to conjure some deep ancestral
memories of the reality we evolved in — a world of abundant life, fresh air and
pure water, home sweet home. Today,
those same ecosystems would look like highways, factories, shopping districts,
cornfields, suburbs — populated by busy mobs of the megafauna known as Homo sapiens. So much has been lost.
Google images also presents many excellent pictures in
response to searches for “megafauna extinction.”
MacPhee, Ross, End
of the Megafauna, W. W. Norton Company, New York, 2019.
4 comments:
Glad I found your blog. Am wandering through the archives as I have time.
Regarding megafauna reproduction rates- You may well have discussed this in a post I haven't gotten to yet, but as megafauna, our reproductive rate will return to the long term norm once the fossil fuel "fertilizer" effect has ended. We are after all, an apex predator, and will get back in balance with our food sources.
Depending on how much, and which technology we hang on to, there is a chance it could be a pleasant outcome. ( I guess pleasant is a relative and subjective term :) )
Hi Steve! Welcome aboard. Pleasant outcome? You must have gotten one of those 50 pound sacks of Chinese hopium. I hear it’s good shit.
I agree that we’re getting close to Peak People, and my blog often discusses this. Here are a few samples:
The Coming Famine
The End of Plenty
The Rapid Growth of Human Populations
Ha! No hopium here. It is apparent to me that multiple trend-lines resulting from fossil fuel use and resulting population explosion will not end well.
I was more thinking about (a few hundred ?) years from now after the die off and rebalancing, that it would be nice if a bit of science knowledge was retained, and a culture might develop that had retained some lessons and intentionally chose a path more in collaboration with the rest of nature.
Granted, the folks in this scenario might well be settled along the shores of the northwest territories and siberia, eating from polyculture plantings of a tropical sort.
The bike path often takes me close to a busy interstate highway. Everything in those trucks will end up in landfills, or waterways, or the atmosphere. Ditto for the cars and semis. It will be good when the pavement sprouts greenery, and the traffic is wildlife. It will be nice when the noise of industrial civilization fades out, replaced by the music of birds, breezes, and coyotes. When the lights go out forever, the magnificence of starry nights will return.
I was just reading about a Girl Scout field trip. Girls with AIDS from Los Angeles were taken to a camp in the mountains. One night, a nine year old girl woke up, and had to go to the bathroom. Stepping outside, she looked up and gasped. She had never seen stars before. She was a changed person. From that moment on, she saw everything. She used her senses. She was awake.
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