Monday, September 16, 2019

End of the Megafauna



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 na├»ve 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.

Sunday, September 1, 2019

Wild Free and Happy Sample 22


[Note: This is the twenty-second 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.] 

Mother Grassland

Hominins originated on the tropical savannahs of Mother Africa, about four million years ago.  Since then, we have evolved, gotten too clever, colonized six continents, driven many megafauna species extinct, maximized food production, and exploded in numbers.  The human saga has been a unique experiment in living that is entirely out of the pattern of all other animals.  In a fantastic joyride of blissful ignorance, we have unintentionally succeeded in rubbishing the planet.  The bedrock foundation of this grand adventure is our deep and enduring relationship with grassland ecosystems.

Grasslands are sprawling green arrays of solar energy collectors that transform sunbeams into carbohydrates.  These nutrients migrate from species to species, up and down the food chain, and enable the existence of the family of life, including large herbivores, the preferred food for prehistoric people.  For the effort invested, they provided the biggest jackpots of meat.  Our intense desire for these animals, and our ongoing dependence on them, guided our evolution from hominins to humans. 

It’s important to understand that herds of large herbivores do not usually reside in forests or jungles.  Large body size is an advantage on grasslands, but can be a disadvantage in dense woodlands.  In terms of vegetation, forests contain much more plant biomass than grasslands, but most of it is elevated out of the reach of hungry herbivores. 

For herd critters, grasslands are the best place to dine on high quality greenery, hang out with friends and relatives, and enjoy a wonderful life of fresh air, travel, and adventure.  Each year, grasslands produce much more new biomass per acre than forests, and it’s conveniently located close to the ground.  Consequently, grasslands are home to far more large animals.  I would expect that most mammalian megafauna species originated in grasslands.

Grasslands, grazers, and large carnivores coevolved for many millions of years.  Much more recently, hominins pushed into the game, and began competing with the carnivores.  By and by, the clever tropical primates, with their terrifying weaponry, expanded into every continent, migrating from grassland to grassland, hunting, feasting, singing, and dancing.

As expanding wild cultures perfected their hunting skills, large game became harder to find, and attention shifted toward smaller animals, birds, shellfish, and so on.  We kept bumping into limits, and some cultures began to lurch toward the domestication of animals and/or plants.

Over time, persistent control freaks eventually succeeded in domesticating some wild herbivore species.  Instead of spending their time chasing increasingly scarce wild critters all over the countryside, they could selectively breed passive dimwitted animals, confine them to limited pastures, and conveniently exploit them in every imaginable way.  Jared Diamond noted that the five most important domesticates were horses, cattle, sheep, goats, and pigs.  All five were domesticated on the grasslands of Eurasia by 4000 B.C.  No mammals were domesticated south of the equator in Africa, humankind’s ancestral homeland.

In some cultures, foragers gathered the energy-dense seeds of wild grasses.  Over time they encouraged these grasses to grow in more locations by sowing their seeds.  Foragers had a natural tendency to gather the seeds that were more convenient to reap, and leave behind seeds that readily fell to the ground.  For example, when wild wheat is ripe, the heads shatter, releasing all of their seeds.  This natural dispersal promotes the survival of the species. 

Year after year, foragers brought home seeds from plants that were (1) less prone to shattering, (2) ripened at the same time, and (3) produced larger seeds.  Over centuries, the seeds they planted became significantly different from wild seeds.  Today, more than half of the calories consumed by humankind come from three grasses: rice, wheat, and corn (maize).  Other popular grasses include oats, barley, millet, sorghum, sugar cane, and bamboo. 

I’ll have more to say about plant and animal domestication in later chapters.  Here, I just want to point out that some hunter-gatherer cultures transitioned into farmers and herders.  Their diet continued to major in grassland plant foods and large herbivores, but it was shifting toward domesticated varieties.  What remained constant was the continued dependence of many cultures on grassland ecosystems.

Graham Harvey, a grass worshipping wordsmith, concluded that humans are essentially creatures of the grass, like hyenas and horses.  Deep inside, we still are.  Long ago we lost our ability to quickly scamper up trees, and leap from branch to branch.  We evolved into bipedal critters fine-turned for walking, running, and surviving in grasslands.

Nomadic Freedom

In the good old days, bands of nomadic hunter-gathers spent their lives wandering across vast grasslands.  It was a way of life that majored in freedom.  Our ancestors were as free as every other wild critter.  No rent, money, landlords, soldiers, slaves, taxes, kings, police, or smart phones.  Indeed, we evolved as nomads, and remained nomads for almost the entire four million year hominin saga.  For hunters to stop roaming, and put down roots, would have been very risky.  Their best option was to follow the herds, which never stopped wandering in search of grass.

Bruce Chatwin was fascinated by the freedom of nomadic life, and the deep human need to always keep moving.  He was born in England in 1940, and spent his entire life in an intensely overpopulated world, boiling with nonstop conflict and bad craziness.  Industrial civilization tends not to inspire a profound sense of joy, wonderment, and celebration among the billions of anxious stressed-out taxpayers born in captivity.

He mentioned a Hungarian epidemiologist who had studied the history of infectious diseases.  The man concluded that humans were not meant to settle down.  Whenever you confine dense populations of humans and other animals in a fixed location, poop happens — lots of poop — excrement all over the place.  Drinking water develops a crappy flavor and aroma.  Before long, pathogens rush through the crowds, weeding out the weak and unlucky — a gold rush for grave diggers.  Nomads live in small bands, and rarely crap in the same place twice.  Their water tastes like water, and their lifestyle is not a magnet for infectious diseases.  Freedom is good for your health.  We’ll take a closer look at disease in later pages.

Today, during the brief era of fossil fuel mania, developed societies can temporarily discourage epidemics by implementing complex, expensive, energy-guzzling systems for waste treatment and water purification.  In wealthy societies, antibiotics are currently controlling the spread of many pathogens, but the benefit of these wonder drugs can only be temporary, because pathogens will never stop mutating into drug-resistant forms.  We are approaching the post-antibiotic era.  Whistling while he works, the Grim Reaper is sharpening his scythe.  Breaking all the laws of nature has harsh consequences, and Big Mama Nature has a deep regard for justice.

Finally, nomadic cultures enjoyed great freedom as long as they remained hunter-gatherers.  These cultures were essentially egalitarian.  There was no hierarchy of power, everyone was equal.  Unequal status was toxic to group cohesion.  Folks who became big headed were a serious problem that had to be promptly resolved.  It was vital that folks in small bands cooperated, shared, and respected one another.

When nomadic cultures shifted from hunting wild animals to herding enslaved critters, they entered a path that led to ugly destinations.  Nothing more reliably turns humans into tyrants, conquerors, egomaniacs, and spectacular idiots than cultures that define personal status in terms of accumulated wealth — personal property.  The lad with 100 cattle looked down on the fellow with 10.  This mindset sparked an explosion of craziness — furious empires of Mongols and Huns spilling rivers of blood.  Status mania continues to this day, but on a dramatically larger scale.  We are not living at the zenith of freedom, or anywhere near it.

Grassland Basics

In the dry land regions of Earth, there are four primary biomes: grassland, forest, desert, and tundra.  Precipitation is a key factor.  Forests and jungles need to receive at least 30 inches (76 cm) per year.  Deserts receive less than 10 inches (25 cm).  Grasslands fit in the middle, 10 to 30 inches.  Grasslands have two seasons, productive and dormant.  In warm climates, they are dormant during the dry season, and recover when the rains return.  In temperate climates, they are dormant during the frosty months, and green when the soil thaws.

Grasslands have evolved to survive in arid climates.  Grasses can live where most other plant species cannot.  There are three basic categories of grasslands: savannah, steppe, and prairie.  [MAP]  Savannahs are grasslands speckled with some trees and brush.  Steppes are called shortgrass prairies, because most plants are less than one foot (30 cm) tall.  Prairies are wetter, and produce tall grass, which can grow up to 13 feet (4 m) high — a horse can disappear in it.

Graham Harvey noted that grasses first evolved about 70 million years ago.  There are now an estimated 12,000 grass species, and they grow in many temperate and tropical regions.  Grasslands are communities of different plants — primarily grasses, mixed with a wide variety of sedges and leafy forbs (wild flowers and herbs). 

These mixed communities maximize the capture of solar energy, make better use of soil resources, and create rich humus.  Humus boosts fertility, and helps retain moisture.  Some plants convert atmospheric nitrogen into a form that is essential for all plants and animals.  Others are good at retrieving essential mineral nutrients.

Following an intense disturbance, grasslands can recover in 5 to 10 years — far faster than a wrecked forest.  Evolution has done a remarkable job of fine-tuning grasslands for rugged durability.  They can go dormant during dry times, and revive when rains return.  They can survive extended droughts and six month winters.  They can recover more easily after wildfires because only a third of grassland biomass is above ground, and vulnerable to flames. 

Beneath the surface, the invisible portion of grasslands is astonishing.  Many plants send roots deep into the ground, to acquire moisture and nutrients.  Some grow as deep as 32 feet (10 m).  In some regions, densely interwoven roots created a thick sod that pioneer farmers cut into bricks that were used to build homes and schools.  Because of unreliable precipitation, trees and shrubs often die before they can grow roots deep enough to tap dependable water.

The seeds of many grassland species can remain dormant for an extended period, until appropriate conditions return, and inspire them to germinate.  Some seeds can survive a ride through an herbivore’s gut and remain fertile, enabling the colonization of new locations.

In 1872, Kansas senator John James Ingalls celebrated the power of grass.  He wrote: “Grass is the forgiveness of nature — her constant benediction.  …Streets abandoned by traffic become grass-grown like rural lanes, and are obliterated.  Forests decay, harvests perish, flowers vanish, but grass is immortal.  …The primary form of food is grass.  Grass feeds the ox: the ox nourishes man: man dies and goes to grass again; and so the tide of life with everlasting repetition, in continuous circles, moves endlessly on and upward, and in more senses than one, all flesh is grass.”