In the past, different societies and cultures have used different strategies to control population size. Pederasty was used by ancient Greek societies, preventing marriage in men until later in life. This cultural practice has even been used more recently in Siwan. Other approaches have included emigration, expansionism and technological developments. Technology has allowed for the Green Revolution of the last three decades. However, these same agricultural “improvements” have caused water deficits, soil degradation and peak oil issues.
Nature has historically been the means by which population has been controlled. Infectious diseases like bubonic plague and influenza have repeatedly reached epidemic proportions, killing sometimes significant portions of populations. New diseases such as SARS, AIDS and avian flu can still reach epidemic proportions in our lifetime, despite advances in medical technology. Plant pathogens and pests can also have devastating effects on food security. Locust swarms can be just as devastating now as they were in Biblical times.
Weather variations have seriously affected crop production. Minor yearly variations can have huge affects on crop production and result in either feast or famine. Shifts in climate patterns have resulted in the collapse of entire civilizations, like the Mayans and SW Pueblo Indians.
Humans themselves have regulated their own numbers for as long as we have been humans. War, moral attitudes, genocide and the depletion or pollution of natural resources have affected population. Modern technology allows us to control our birth rates. The use of effective contraceptives and medical sterility make population control possible, even while we have removed natural selection, decreased birth mortality rates and increased average life spans.
China's one-child policy sounds like an interesting idea for controlling soaring populations. However, upon closer inspection there are many exceptions to this policy, and China's current birth rate is closer to 2 (1.6-1.9 depending on the source) than 1. This policy was originally meant to be in place for one generation, and China estimates that it has three to four hundred million fewer people today as a result of the policy. However, exceptions are made for certain ethnic populations, single-child parents are allowed two offspring, and many families can pay fee to have more than one child. Also, many female babies are still put up for adoption, and do not count towards the one child policy if their births were never reported. China reports that they have historically had best results at population reduction through a combination of poverty alleviation and health care with relaxed targets for family planning.