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I previously mentioned the notion that humans are creatures of the grass. Recently, I stumbled on information that added a deeper dimension to this theme. It all began when I read that the area of global forest cover has been sharply reduced since the early Miocene Epoch. This stimulated my curiosity, and led to an exciting wild factoid chase. The Miocene spanned from 23 to 5.3 million years ago. It seems that the early Miocene was wet and warm, and many ecosystems were forests. I was surprised to learn that as late as 20 million years ago, much of Antarctica was covered with temperate forests.
Anyway, later in the Miocene, maybe 6 to 8 million years ago, it got cooler and dryer, and a new type of major ecosystem emerged — grasslands. They can thrive where it’s too dry for trees. Over time, expanding grassland displaced large areas of forest. This shift was an important turning point in the human saga. As forests shrank, there was less habitat for tree-dwelling primates, causing a number of species to tumble off the stage. Some primates moved out onto the savannah, and figured out how to survive in open country as ground-dwelling primates. They included the ancestors of baboons and humans.
So, it was a gradual but substantial shift in climate patterns and ecosystems that made it possible for our ancestors to invent a new career path as hunters of large herbivores. As the climate got cooler and dryer, grass species more tolerant of arid conditions rose in importance. At this point, we need to take a brief side trip into some technical stuff. I’ll keep it as short and simple as possible.
The entire family of life is solar powered. Incoming solar energy is received by green plants, who use it to produce sugar. This process is photosynthesis. It converts solar energy into a form of chemical energy that plants and animals must have in order to survive. Some animals acquire it directly by eating plant material, and others get it indirectly by dining on plant-eating animals. Thus, photosynthesis is the foundation of life on Earth.
The process begins by splitting water molecules (H2O) into hydrogen and oxygen atoms. Then, in a fancy magic act, hydrogen is stirred together with CO2 to make sugar (C6H12O6). The process results in some leftover oxygen atoms, which are released to the atmosphere. Notice that animals exhale the CO2 that plants must have, and plants exhale the oxygen needed by animals, a sacred circle dance. Plants can use the sugar to fuel their growth, or they can convert it to starch, and save it for later. Plants can also make fat, protein, and vitamins. They’re much smarter than they look.
The act of snatching carbon from the air, and incorporating it into living plant tissues, is called carbon fixation, or carbon sequestration. As more carbon gets sequestered into the plants and surrounding topsoil, then less of it remains in the atmosphere. This is great, because too much carbon in the atmosphere can lead to catastrophic climate juju, like the freaky changes we’re now just beginning to experience.
I should also mention that petroleum and coal are substances made of sequestered carbon that accumulated over the course of 500 million years. Big Mama Nature wisely stored it away in a safe place deep underground, where it could cause no mischief. Unfortunately, it has become very trendy for ignorance-powered societies to retrieve enormous quantities of this ancient carbon and foolishly burn it up, in order to indulge in a decadent joyride of self-destructive childish whimsy. Big brains can make big mistakes. It’s so embarrassing!
And now, (gasp!) the plot thickens. There are two categories of plant species, based on the mode of photosynthesis they use: C3 or C4. C3 produces a compound that has three carbon atoms, and C4 produces a compound that has four carbon atoms. Both types are very old, but the shift to a cooler and dryer climate greatly boosted the expansion of C4 species. Maybe 85 percent of the plant species on Earth are C3. Their method of carbon fixation is simpler and less efficient than C4.
Elizabeth Kellogg studied C4 plants. In one experiment she found that, under ideal conditions, C3 plants could theoretically capture and store up to 4.6 percent of the solar energy they received, while C4 plants could get up to 6 percent (i.e., 30 percent more than C3). While only 3 percent of flowering plant species are C4, they account for 23 percent of all carbon fixation in the world. In other words, they produce much more of the precious chemical energy (sugar) that the family of life depends on. Kellogg calls the C4 process a turbocharger.
There are four conditions under which C4 plants have a big advantage — high temperature, high light, low moisture, and low nutrients. Because they use much less water, C4 plants better conserve soil moisture. They also produce more root biomass, which increases their tolerance for drought and fire. Of the 12,000 grass species, 46 percent of them are C4, and they include corn (maize), sugar cane, millet, and sorghum. (Mad scientists are now trying to alter DNA to make rice C4 too.)
When critters consume C4 grasses, this diet leaves behind physical tracks. Spencer Wells wrote that the bones of Native Americans revealed whether they were corn farmers or hunter-gatherers. Because corn is a C4 grass, the bones of corn eaters contained molecular C4 markers. Baz Edmeades talked about the ferocious dirk-tooth cats (Dinofelis), a species that went extinct about 1.4 million years ago. We know they were creatures of the savannah, not the forest, because analysis of their tooth enamel indicated that they dined on herbivores that ate C4 grasses.
And now, dear reader, at long last, we are ready to proceed to the exciting conclusion of this tedious jabber. It’s time to turn the spotlight on the heroes of this story, the C4 grass species. Kellogg noted that in the last 8 million years, as climate change drove the retreat of tropical forests, the domain of C4 grasses has greatly expanded. They are now significant components of major grasslands around the world.
C3 grasses were better adapted to moist forest floors and limited sunlight. They were less able to thrive on arid grasslands. Out on the savannah, conditions were ideal for C4 grasses, because they needed less water to enjoy a happy life. Here they moved from the sidelines to the center stage. Receiving many hours of direct sunlight every day, they were able to manufacture generous amounts of chemical energy (sugar), and this gave them the ability to grow rapidly.
And so, these highly nutritious grasses became a highly desirable food source for the animals that were able to digest them, which required some adaptations. Baz Edmeades noted that the blades of these grasses were tough, highly fibrous, and coated with abrasive silica. Evolution responded by providing some animals with new and improved teeth that were more tolerant of abrasion, and better able to pulverize the plant fibers. Other critters were issued new and improved digestive tracts, populated with bacteria that were fine-tuned for chemically breaking down fibrous glop. The critters that succeeded in adapting to the new banquet made big gains in size and diversity.
Of course, too much of a good thing will have consequences. If herds got way too large, the vitality of the grassland would be degraded, leading to starvation. So, evolution came to the rescue by promoting a variety of big strong bloodthirsty carnivores, who delighted in inviting large herbivores to join them at lunchtime. To make this sacred dance more sporting, evolution also encouraged the development of herbivores who could boogie across the grassland at high speeds.
Edmeades concluded that the rise of highly productive C4 grasses radically changed the world. It spurred the evolution and spread of an astonishing variety of grassland herbivores and their predators. It led to the emergence of spectacular Serengeti-like ecosystems in Africa, Eurasia, and the Americas — fantastic wonderlands of abundant life.
Graham Harvey noted that the herds of grass-eating critters benefitted the grasses. Grazing actually stimulated plant growth. In a brilliant design, new blades of grass emerge from growing points located close to the ground, where they are less likely to be damaged by hungry teeth. The faster that grasses can send up new blades, the more sunlight they can capture, the more sugar they can make, and the happier the whole ecosystem becomes.
Grazing also benefitted grasses by regularly nipping off the rising shoots of woody vegetation. If trees and brush were allowed to grow and spread, they would compete with the grass plants. Then, the herds of hungry herbivores would have less to eat, and so would the carnivores that adored red meat. Herds religiously offered their deep gratitude to the grass people by lovingly depositing nutrient rich manure and urine all over the place.
The big picture here is that the shift to a cooler dryer climate encouraged the substantial expansion of grassland, which boosted the expansion of C4 grass species, which propelled the evolution and expansion of large grazers and carnivores, which boosted the global tonnage of living meat. These megafauna migrated and settled on five continents (not Australasia). Around the world we find species of horses, bison, elephants, antelope, deer, hyenas, wolves, bears, and so on. The moral of this story is that climate change can radically alter the face of the planet, and the family of life.
Later in this amazing transformation, another powerful agent of radical change joined the cast of the grassland soap opera. These critters walked on two legs, and resembled what you see in the mirror. They eventually assumed the role of apex predators, something that no other primate had ever attempted. Our ancestors did not wait patiently for evolution to provide them with the speed, strength, fangs, and claws that are customary for natural born carnivores. Instead, they invented hunting weapons, learned how to make fire, and began experimenting with a way of life that no other animal in the history of the planet had ever attempted. It’s notable that every other animal species continues to live like they did a million years ago — ultra-conservative, and perfectly sustainable.
The advance of the new critters marked the emergence of an extremely spooky, highly contagious, multi-drug resistant virus known as cleverness fever. For a few million years, its mind-altering effects gradually intensified. Ten thousand years ago, they surged. Today they are skyrocketing. Humankind is now engaged in full scale warfare against the entire family of life, including itself. A lively and entertaining soap opera has shape shifted into the mother of all horror shows. Will the current swing to a much warmer climate provide the miraculous silver bullet cure for the mass hysteria of cleverness fever? Stay tuned.