No Such Animal

Today’s post is a bit of a deviation from gardening, but important to understand the broader issue of who we are and how humans fit into the ecosystem. Humans have a wide array of traits that make them distinct from other animals. Any one trait can usually be found in another species, but combining them all together in one package has made us a formidable organism quite unlike anything the planet has seen before. The history of life on Earth is full of species that made apparently sudden breakthroughs that gave them tremendous advantages and in some cases endangered the functioning of the entire biosphere. The first green photosynthetic algae produced so much oxygen that the reversed greenhouse effect nearly froze the planet solid. When plants first evolved wood it took fungi tens of millions of years to catch up and learn how to break it down again, leaving the planet littered with debris that makes our current debates about plastic seem trivial. Trilobites were the first animals with slicing jaws and they put them to great use chewing through every other soft bodied species that came before them, driving many whole families to extinction as they proliferated. Humans are just the most recent species to take this kind of leap and stir up the planet.

The most distinctive physical adaptation of humans surprises most people when it is pointed out. The part of our body that looks the least like anything else is of course our feet. This made the foundation for our change in locomotion to dedicated bipedalism. This had the biggest effect in greatly increasing our energy efficiency while in motion. A human uses about half as much energy as a comparably sized quadruped over the same distance. This combined with a highly developed brain to allow humans to forage over longer distances than most mammals and arrive in the right place and time to exploit seasonal resources. The genes used to form the legs are also used to create the arms, so the period of evolution of the foot also spurred changes in the hand, leading to our highly dextrous tool making ability.

Another major change with humans is a reallocation in how energy is used in the body. The metabolic rates of mammals scale fairly predictably with body mass. An animal of a particular size cannot increase the amount of energy it uses beyond a certain point since the total amount of heat generated could not be dissipated quickly enough. Instead if an organism wishes to use more energy for one purpose it needs to use less energy for another so the total energy consumption remains fairly constant. Humans made a major trade off by reducing the amount of energy used by the digestive system and reallocated it to run our enormous brains. Despite their high size relative to body mass our brains are also remarkably energy efficient, packing more brain cells into a smaller volume than other mammals and using less energy to run them than expected.

This trade off set us up for our need to pre-process our food before consumption. Cooking on a fire is the most common way to do this, but fermentation, leaching, grinding and a wide range of other tool and hand dependent techniques contributed as well. Humans are unusual in being especially good at digesting large amounts of starch, with multiple copies of relevant enzymes. This mutation also occurred in domestic dogs, most likely as they gathered with us around a camp fire roasting tubers and seeds. The ability to unlock an abundant energy source in the form of otherwise toxic and indigestible tubers and seeds, using an even more abundant untapped energy source in the form of fire wood, gave us a massive advantage over all other species. The flexibility of our food processing techniques made us in effect the universal herbivore, able to eat just about any plant in any ecosystem. By contrast other mammals were limited to physical adaptations in their jaws, digestive systems and metabolisms to deal with a much narrower range of plants (for example sheep are grass specialists while goats are shrub browsers). Instead of ten species of specialist antelopes grazing together you can have one ultra-generalist human species eating everything.

This ability to tap into a wide range of energy sources turbo-charged our complementary ability to hunt. Specialist predators like lions also need to make investments in adaptations to catch and consume prey, leading to inevitable specialisations in which type of prey they can handle. Humans instead with their highly flexible and adaptable hunting techniques and tools could rapidly switch between prey species, making them in effect universal carnivores. As large species were driven to extinction techniques such as archery and hunting dogs developed to shift to smaller and more difficult prey. Normal specialist predators are kept in balance with their prey since their population cannot exceed the capacity of their prey to feed them. Humans have no such restriction since we can continue hunting a species to extinction while maintaining our population with starches and by shifting hunting to other species.

The impacts of humans outside of our region of origin in Africa were rapid and dramatic. Hunting led to the extinction of megafauna everywhere else we went, and more rapidly after the arrival of humans the further you get from Africa. It is likely that African animals evolving alongside humans as our hunting skills increased had an opportunity to learn how dangerous we could be before going extinct. Seeing historical records of how naïve animals on isolated islands showed no fear of humans even as they are being slaughtered gives a hint of the dynamic when humans first reached Australia and the Americas. The loss of keystone herbivores and predators completely upended the ecology wherever humans went. Without the pressure of herbivores the vegetation types shifted dramatically, often transitioning to fire dependent ecosystems since so much biomass was going uneaten. Mineral cycling and transport was also impeded, further damaging the productive capacity of the land. These changes set up the conditions that favoured agriculture, and agriculture in turn created the conditions where industrialisation made sense.

Coal and oil were known of and used for minor roles for thousands of years before the industrial revolution. For a long time coal was considered totally inferior to firewood as it was difficult to light and produced an acrid smoke. The transition away from wood was forced by a simple depletion of forests in Europe. Humans once again shifted their primary energy source as they depleted their previous one, leading to ever more extraordinary population sizes and allowing us to travel across the entire planet like never before. Scientists once dreamed of an inevitable shift to other energy sources such as nuclear fission or fusion, or now that they haven’t arrived as promised various forms of renewable energy are being touted as replacements. It may instead be that we have finally run out of luck and this time there isn’t anything else left to burn. Our civilisation wouldn’t be the first to collapse back into the dust from which it rose. And the people left behind who cobble together a new way of life at a lower level of complexity wouldn’t be the first to do so either. It is with this possible future in mind that I pursue the goal of zero input agriculture, where growing food and managing landscapes does not depend on subsidies from our pervasive industrial system. To succeed we must be unafraid to experience failure, especially while we still have the luxury of failing without disastrous consequences.

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