For 99.99% of the two million years that humans have been around, the entire species lived in harmonious balance with nature — that is, perpetually on the edge of starvation, acquiring the bare minimum of sustenance necessary to sustain the present population.
Every now and then, a change in the environment, a new disease, or perhaps a tribal conflict caused a mass die of some percentage of the population. This provided a rare opportunity for a surplus of food to become available, and the population quickly grew in prosperity and (presumably) happiness until the ecological balance was restored and the state of constant near-starvation returned.
But then — after a few hundred thousand years of building ever complex tools, homo sapiens sapiens was able to sustain a surplus of food production despite unprecedented population growth. Whereas it has previously taken a million years to add an additional million sapiens to the population, now each additional million was added in about a month.
The 200 years following the industrial revolution saw accelerating productivity improvements which led to accelerating capital accumulation, which incredibly, allowed per capita wealth to grow faster than the population, raising the standard of living in industrial countries over a hundred fold.
Now, unless you happened to grow up in a remote Amazonian tribe and then somehow integrated into modern society and managed to read this on Facebook, you have no idea what a “hundred fold improvement in the standard of living” means. You probably went camping, or saw a romantic nature documentary and think that lack of indoor plumbing, having an average of 80% of your children die in infancy, habitually going up to a week without food, being left for dead after major injuries or old age, and lack of Facebook access is not that big of a deal. Maybe it isn’t – I don’t know either.
Anyway, for biological or cultural reasons, we tend to extrapolate our current status of ecological surplus and assume that it will continue indefinitely, despite having experienced it for only .0001% of human history. In fact, economic incentives suggest otherwise: in the long-run, social groups which value higher reproductive rates will eventually dominate the human population and return homo sapiens to subsidence levels. We might still have Facebook, but we’ll be back to perpetually surviving on edge of starvation, save for the brief times after a catastrophe kills of much of the population and we can thrive on the surplus capital.
Any group that values large families will tend to dominate the species given sufficient time. It might be the Mormons, Amish, Hutterites, or probably some new group that places an explicit value on maximizing the reproductive rate at the expense of all other values. Unfortunately, having as many children as biologically possible does not correlate with other values that most of us consider desirable, but that is how ecology works.
Some have suggested population controls, but those would only work with a dictatorial single world government, and those are hard to sustain indefinitely over geological time spans. In other to avoid a return to the state of nature, we must either sustain the present excess of capital growth over population growth indefinitely, or find a way to permanently limit the population size. Since the earth is of finite size, sustaining the surplus capital growth requires the difficult task of colonizing the entire universe. On the other hand, it might be even more difficult to restrict the reproductive rate, given that any group which violates the restriction could gain control over the whole planet.
In the developed world, population growth is not a problem. Capital growth stays well ahead of population, because birth control has effectively replaced infant mortality, famine and war. In Japan and much of Europe, population has peaked and begun to decline, and average age is increasing so that demands for inter-generational transfers may threaten social stability more than absolute scarcity.
Without fundamental changes in our understanding of the Universe, moving the human population off of the Earth is a very remote prospect. Moving a single human body to the nearest, neighboring star system requires incredible resources. Moving millions is difficult to imagine outside of science fiction. Even populating our solar system beyond the Earth is a very remote prospect, so if populating the Universe is our only hope, we have very little hope.
Fortunately, little evidence supports the incessant talk of a dying Mother Earth. I remain very skeptical of claims that humanity has exceeded or threatens to exceed the Earth’s capacity to support us. Development may instead continue and population may peak and then decline long before we reach such a limit, and we need no statutory program of depopulation for this purpose.