Humans have also sought to limit certain species' population growth through applications of pesticides, disinfectants, sterilization, extermination, or other eradication methods. At times they have used such measures even against fellow human beings. But there are naturally many cultural, moral, or religious constraints against these and similar approaches.

Doubtless it is merely coincidence, but an irony of the modern world is that, for whatever reasons, much more expense and effort has gone into the development of highly efficient means of killing vast numbers of people than into how we might limit the number of births, if only through voluntary abstinence. A culture of life, from one point of view, has thus often been accompanied by the creation and use of extreme approaches for the curtailment of life, from another viewpoint.

Per "Population Growth Rates and Doubling Time," by Matt Rosenberg, in "About - Geography - Population Growth," 1/2/06, the rate of population increases reached a peak in the 1960s, at greater than 2% a year. At that time humans were having so many more births than deaths that, if this excess had persisted, the population would have doubled every 36 years. It has come down by now, but still the birth rate is high enough that, given lifespan trends, unchecked current fertility rates would mean multiple trillion humans by the early 2400s. This is a far-fetched figure, of course. It cannot happen that way. Instead, like all others in nature, the human species must one day, sooner or later, achieve equilibrium. From a practical persepctive, the alternative is simply extinction.

Science fiction aside, outer space is not actually available to the vast majority, and, even for a few, establishing and maintaining a viable human toehold on far distant planets would likely consume far more resources than the habitable surface of our own sphere, much less the national budget of one country, can realistically provide. So, the question is, as we foresee at some point in the next 10 to 100 years limits on Earth within which our kind must, willy nilly, achieve equilibrium or perish, how shall it be achieved, or shall the choices be left, by default, to nature?

The injunction to "go forth and multiply" was a positive maxim when our species was relatively young, inefficient, and newly competing with many other, then more dominant animals. Now that there are 6½ billion of us and our activities threaten to overwhelm much of the biosphere, has the time come for less aggressive means of attaining equilibrium than simply by having one more, far more destructive world war after another? Tens of thousands of nuclear warheads and missiles to deliver them have been made, more than enough to kill indiscriminately every person on the planet many times over. Besides these, biological and chemical weapons, terrorism, "sanctions," and genocide are now all being deployed for or used effectively to control populations, while the quality of life for many remains meager, and the gulf widens between the haves and the have-nots. Are these destructive preparations and behaviors, all of which can be justified with high-sounding spin, not really so much under our control as they are nature's way of saying (as with aging): "Aren't there enough of you yet?"

Surely there is a better way. Nobody is recommending people be chosen by lottery for early demise. Nor would I, if I had children, want to give up any for the cause. And there is certainly not a single of my nieces and nephews whom I would wish had not been born so as, to quote Scrooge, "to decrease the surplus population." In most instances of which I can think, I personally would also be against abortion.

Yet it may be irresponsible to merely leave to future generations the consequences of our species' current habits of having more children than the "spaces" being vacated by natural deaths.

Whether by abstinence, mass devastation, or other measures, Homo sapiens would seem to be approaching the point beyond which the number of deaths must go up or the number of births go down, according to "UN Warns of Population Surge," in "BBC News," 12/9/03. I do not know what number of people is a sustainable, equilibrium level. Currently our population, with great variation from one region to another and an overall growth rate of over 1%, is doubling about every 50-60 years. At present human fertility levels and barring either a substantial exchange of weapons of mass destruction or a horrendous natural catastrophe, we'll be 50 billion by 2186, even without further longevity improvements.

Some have argued the world can only bear, on a long-term basis, 1 billion people, some 10 billion, many a number in between. But the sustainable figure surely is not 50 billion, and so the rate at which our population increases must be reduced. The sooner this occurs, the more we may decide the extent to which we alter the planet to suit our particular species' ends, and with fewer adverse side-effects. If not now, when? People like to point to geopolitical crises of one kind or another as the reasons things are not better for most in the world than they are, but what about there being just too many of us, all naturally wanting to have the good life for ourselves and those about whom we care?

We are in some contention with China over its demands for the same commodities we feel are needed for our citizens. But imagine how significant would be our difficulties with that Asian behemoth if, instead of 1.5 billion, it were needing to look after the expectations of 3 billion mouths. Much as I decry the methods it used, were it not for China's measures in recent decades to assure a greater equilibrium of its population, that country's numbers would dwarf the needs of every other nation and probably would exert a powerful influence on its leadership toward an aggressive foreign policy.

Though we do not wish to suggest any sort of planning steps, had the last few decades in Mexico seen a natural inclination toward a more average birth rate, chances are millions from that economically-strapped country would not have felt it necessary to cross Mexican and US deserts, at grave risk to themselves and their children (many of whom die on that trek each year) to reach the comparative plenty of a nation to the north with a birth rate (except for immigration) only about one-fourth to one-third as great as the state they left.

We are even now, with a global population growth rate of just over 1% annually, running short of sufficient refined oil and natural gas, potable water, nutritious food, clean rivers, plentiful forests, wetlands, copper, steel, and clean air. Even our vast oceans are being changed dramatically in ways quite unhealthy for the species that try to live there.

Arguably too, with arithmetic growth in the world's population there are geometric increases in global warming, political or military tensions, and environmental degradation.

The good news is that fertility is not an etched-in-stone factor but rather is mutable. As families become healthier (especially with lower infant mortality), more educated, and better off financially, there is a perhaps counterintuitive tendency for them to choose to have fewer babies. The potential problem might thus eventually take care of itself.

In the interim, though, we have at least a few difficult years or decades ahead as our numbers are going up but our commodities and services cannot yet increase fast enough to cope with the enormous demand. And unless we can somehow improve the standards of living for most people, and quickly, old cycles of poverty, hopelessness, malnutrition, and ill health may paradoxically lead as well to a persistence of more births than can be sustained.

It is probably not just chance, for instance, that Afghanistan, where, even after the 2001 invasion and victory, conditions for the average person are in many ways dire, has one of the highest annual population growth rates in the world, at 4.8%. Again per the "About" article, if nothing is done to achieve sustainable equilibrium, that poor nation will have a population of over one billion by 2078. Whether there or elsewhere in the world, how many more Osama bin Ladens might be harbored under the stress of that kind of population pressure?