My efforts to explain and project global trends in population and consumption have yielded two competing stories about the past and our potential future. With critical new insight about the second one emerging from work over the past week that may have reconciled the two, this is a good time to summarize them.
The stories are based on several key observations. First, happiness (life satisfaction) varies predictably with the amount of resources people consume, as measured by their ecological footprint, with smaller and smaller increases in happiness as consumption increases, approaching a maximum amount as any one person approaches consumption of the output of Earth's entire biosphere. Second, there is a minimum amount of such resources each person needs to survive. Third, the population of an average other species decreases linearly with the total amount of resources that humanity consumes. Fourth, global economic activity is proportional to the square of the product of population and happiness, which I interpret as transactions of artificial environments that provide happiness. Fifth and finally, in small groups life expectancy increases with consumption much as happiness does, while in large populations it varies with the total resources consumed by the group.
The first story comes from mathematically simulating "worlds" that each represent a point in time with a certain population, ecological footprint, and total amount of resources. A world can only "exist" when: (1) the resources consumed by the population is no greater than the total resources; (2) an average "person" consumes no less than the minimum; and (3) average happiness is less than the maximum. As total resources decrease, the number of worlds decreases, and the remaining worlds are clustered around more restricted combinations of population, ecological footprint, and happiness. Using historical data to identify the worlds occupied by humanity over time, it appears that as our species has consumed more resources, it has targeted the most dense concentrations of remaining worlds, with the objective of occupying as many worlds as possible without decreasing population in the process.
Behind both narratives is a more conventional backstory. All species collect and recycle energy and material, using it to exist as long as possible and to maximize the propagation of their forms over time and space. As the distribution and types of energy and material change, they adapt by changing their behavior and their form (evolving). From the perspective of members of any one species, other species either assist them, impede them, or are merely parts of their background environment that may assist or impede them later. "Assistance" can understood in economic terms as the provision of products and services, collectively considered as "resources" that include food (a primary source of energy and material) and purification of water (processing a resource for use and eliminating threats to survival), and those resources can be provided either on a continuous basis or a one-time basis. "Impeding" includes removal and degrading of resources (or the species that provide them) and, of course, being treated as a resource yourself. Happiness, as experienced by us and possibly other species, is a consequence of the degree that an individual's environment is optimally suited to maximize personal longevity and propagation of the individual's unique characteristics, and increasing it means using as many resources as possible.
The second story begins with two people, each using the minimum amount of basic resources (such as nutritional food, water, and breathable air) needed to live long enough to produce two more people and keep them alive long enough to survive on their own. Those resources are provided by a core set of other species ("supporters") which are doing the same thing and consuming resources supplied by another set of species ("producers"). For the system to last a long time, the supporters and producers must be allowed to reproduce so that their populations remain at least constant, otherwise the amount of resources drops, as do the populations of the creatures that depend on them – especially us.
Consuming the minimum amount of basic resources corresponds to a minimum level of happiness and lifespan, since none is left over for significantly altering an individual's environment beyond providing basic needs. The creation of physical and social technology (such as economics), especially since the beginning of civilization, has enabled the use of more resources as well as other types of resources besides the basic ones. This has translated into increasing happiness, longer lifespans (due to better health care, protection from predators, and a more reliable food supply). It has also supported larger populations, whose labor and ingenuity (higher probability of smarter and more capable people being born) has reinforced technology creation and use.
While we've so far protected the species that provide basic resources, we've consumed more than what other species produce, and have been consuming members of those species themselves. This consumption has included conversion of source material and energy into forms ("waste") that cannot be recycled by other species in a timeframe useful to humans, and may be harmful to them, even to the point of killing them off.
This brings us to the most important aspect of the second story. Humanity is now on the verge of consuming the producers that keep the supporters alive. Keep in mind that only the basic resources keep us alive and healthy; the other resources increase the quality and length of individual lives, and they enable growth in population by getting access to more resources. What will happen next?
In the first story, humanity is forced to retreat to a lower-consumption "world" which allows other species to grow back partially, thus providing resources for more people. We try to occupy this new world and then do the same thing again, resulting in oscillations in population ("popscillations") with a downward trend to a new value dependent on how much the species can bounce back before we overwhelm them again. If, with the second story, historical population and consumption trends are projected forward in time, humanity consumes some of the producers and stops when after our population drops in response to a shortage in basic resources. Then, after some settling, population and consumption both drop to much lower levels, potentially zero.
My new insight came from trying to understand that last drop, which at best seemed like radical overcompensation. After examining my underlying assumptions and being drawn back to the logic of the first story, I realized that humanity must be seeking a particular goal, manifested as reaching a limit in both population and consumption. Historical data showed that the best candidate was a condition where all that remains in the world is us, what we're consuming, and the supporter species. In short, we don't recognize the value of keeping producers around. Incorporating this into the story resulted in popscillation behavior like that in the first story: population drops in response to lack of basic resources, the species providing those resources partially recover, and the cycle starts over and over again, with an overall downward trend in our population. In this case, continuously increasing individual consumption repeatedly causes attempted overshoot of resources that drives down population in response.
As with someone who is banging his head against a wall harder and harder in the hope that it will move out of the way, avoiding further injury is best achieved by stopping the banging. If we're smarter, we'll avoid hitting the wall the first time (immediately stop population and consumption growth). Following this analogy, if the wall starts to move toward us, which is a conceivable consequence of climate change as species start to die off without our help, we should move backward (reduce our consumption) at least as fast as it is moving toward us. If we're lucky, and emphasize reduction of our greenhouse gas waste, the "wall" may slow down or stop before we are forced to reduce our population.