Large populations lead to the emergence of high density urban centers. It is inefficient to cultivate ever smaller plots of land. Surplus manpower moves to centers of industrial production. A second wave of internal migrants caters to their needs, thus spawning a service sector. Network effects generate excess capital and a virtuous cycle of investment, employment, and consumption ensues. But over-crowding breeds violence (as has been demonstrated in experiments with mice). The sheer numbers involved serve to magnify and amplify social anomies, deviate behaviour, and antisocial traits. In the city, there are more criminals, more perverts, more victims, more immigrants, and more racists per square mile. Moreover, only a planned and orderly urbanization is desirable. The blights that pass for cities in most third world countries are the outgrowth of neither premeditation nor method. These mega-cities are infested with non-disposed of waste and prone to natural catastrophes and epidemics. No one can vouchsafe for a "critical mass" of humans, a threshold beyond which the species will implode and vanish. Luckily, the ebb and flow of human numbers is subject to three regulatory demographic mechanisms, the combined action of which gives hope. The Malthusian Mechanism Limited resources lead to wars, famine, and diseases and, thus, to a decrease in human numbers. Mankind has done well to check famine, fend off disease, and staunch war. But to have done so without a commensurate policy of population control was irresponsible. The Assimilative Mechanism Mankind is not divorced from nature. Humanity is destined to be impacted by its choices and by the reverberations of its actions. Damage caused to the environment haunts - in a complex feedback loop - the perpetrators. Examples: Immoderate use of antibiotics leads to the eruption of drug-resistant strains of pathogens. A myriad types of cancer are caused by human pollution. Man is the victim of its own destructive excesses. The Cognitive Mechanism Humans intentionally limit the propagation of their race through family planning, abortion, and contraceptives. Genetic engineering will likely intermesh with these to produce "enhanced" or "designed" progeny to specifications. We must stop procreating. Or, else, pray for a reduction in our numbers. This could be achieved benignly, for instance by colonizing space, or the ocean depths - both remote and technologically unfeasible possibilities. Yet, the alternative is cataclysmic. Unintended wars, rampant disease, and lethal famines will ultimately trim our numbers - no matter how noble our intentions and how diligent our efforts to curb them. Is this a bad thing? Not necessarily. To my mind, even a Malthusian resolution is preferable to the alternative of slow decay, uniform impecuniosity, and perdition in instalments - an alternative made inexorable by our collective irresponsibility and denial. Racing Down