Language and fire. Darwin considered these the two most significant human distinctions.
As winter passes into spring, we are making biochar from bamboo again. Amended with locally adapted beneficial microbes, it will be our principal soil amendment for the summer and fall gardens. We thin the groves before the annual shoots emerge, taking out the old and dead culms and making more room for new growth. We trim the culms and cut them to one meter lengths. The trimmings are used to build chinampas in our wetlands (from the Nahuatl word meaning "squares of cane") and later we heap dredgings and manures on those islands to help form new soil and produce food islands in the cool aquatic microclimate. The remaining canes feed our kiln.
We build the fire in a wok-shaped earthen pit until it spins a torroidal flame front. By continuously adding bamboo we keep the flame high over the pile, watching secondary ignitions of the gases. We allow no oxygen to penetrate down to the lower zones of the pile where we are making charcoal. The 40-degree slope on the sides of the pit provides the precise fluid dynamic. As the cellulose gives up its volatile elements, they escape as gases, leaving behind a hard, crystalline matrix of carbon: biochar. The biochar will be crushed, mineralized, charged with hungry microbes from our compost piles, and sent to gardens and orchards to perform its thousand-year-long ecological restoration work. We heal our damaged atmosphere, deserts and oceans by giving safe and durable shelter to the microbial soil food web.
Every animal on earth has to budget the energy its draws from food. A human allocates roughly one-fifth of acquired calories to its brain, regardless of whether that brain is doing anything useful or just sleeping. The increase in hominid brain size, beginning around 2 million years ago, had to be paid for with added calories either taken in (with a paleo diet) or diverted from some other function in the body.
One way we found to acquire more calories was with fire. Cooked food, like fermented food, is predigested, or broken into simpler protein chains. For the same amount of calories ingested, a body gets 30 to 80 percent more energy from cooked foods than from raw. As raw foodies know, today that usually shows up as food stored around the belly. But as our ancestors switched to cooked food, with their more vigorous lifestyle, they acquired bigger brains by shrinking their guts. Barrel-shaped apes perambulating on four limbs morphed into narrow-waisted Homo sapiens that ran down game on two.
Charred bone and primitive stone tools in a cave in South Africa confirm the use of fire for cooking one million years ago. Still, most scientists believe fire was mastered much earlier, around the time of Homo erectus, roughly 1.8 million years ago.
The evolution of multicellular animals from single celled amoebae depended on cells being able to sense and cooperate with other cells. They did this by generating an electrical potential across membranes, by pumping out ions. We now know this function in both plants and animals is often carried out by symbiots – tiny, semiautonomous parts of our microbiome. Many of the components needed to transmit electrical signals, and to release and detect chemical signals, are found in single-celled organisms known as choanoflagellates. Our partnership with choanoflagellates extends back around 850 million years.
By 360 million years ago, our reptilian ancestors crawled up onto land, eventually birthing our first mammalian ancestors, about 200 million years ago. These creatures already had extra layers of neural tissue on the surface of the brain. Some of these neocortices were quite large. There were flying reptiles that had both large brains and brain-to-mass ratios larger than ours today.
After the dinosaurs went extinct from sudden climate change 65 million years ago, our primate ancestors took to the trees. Good eyesight helped us catch insects and birds, which led to an expansion of the visual part of our neocortex and better hand-eye coordination. Perhaps that was one of things that attracted us to fire, gave us cooked food, and sent more calories up to our crania. Besides increasing in size, our brains developed more input and output points, synaptic nodes modulated by other sympathetic microbes in our microbiome.
All of which equipped us with an extraordinary ability to integrate and process information and perform deliberative reasoning. We began to identify and search for overarching patterns. We took a step away from our animal ancestors and looked beyond the physical objects in front of our eyes. Among other manipulations of our physical world, we mastered fire.
As homo entered into settlements and tribal societies around 200,000 years ago, our brain stopped growing. Since the last ice age, the average size of the human brain compared to our body has shrunk by 3 or 4 percent. Some think our brain's wiring is more efficient now than it was in the past, but that is far from proven.
More likely this shrinkage marks a gradual decline in our mental abilities. David Geary at the University of Missouri-Columbia theorizes that once complex societies developed, the less able could survive on the backs of their smarter peers, whereas in the past, they would have died or at least failed to procreate. We also know that the more intelligent people are, the fewer children they tend to have. That would gradually augur a decline of about 0.8 IQ points per generation in wealthy societies, which may also be occurring. It certainly would help explain why most US politicians today cannot fathom the philosophical debates of Jefferson, Hamilton, Adams and Franklin about the limits to state power. These were men who lacked Google but more than made up for it by reading the classics in original Latin, French or Greek.
Today it takes 10 calories of fossil energy to produce one calorie of food. We are rapidly losing that fossil energy supply and that suggests we can anticipate a significant drop in available food supply unless we radically change how we acquire food.
We could, for instance, harness the wonders of fire to make biochar, rejuvenate soil fertility with our microscopic allies, and build healthy inner ecologies to make ourselves, and our planet, better prepared for the ever-changing future. Whether we shall, with our diminished brain capacity, remains to be seen.