Overpopulation

Overpopulation is the state of any species exceeding, in numbers, the ecological carrying-capacity of its ecosystem. This is primarily expressed in terms of habitat and food supply available. In conventional predator-prey relationships (most commonly illustrated with the example of foxes and rabbits), increased predator numbers mean that food supply drops and the predator population subsequently starves. The cycle completes as the predator population dwindles, allowing the prey population to recover.

Major factors in the discussion of human overpopulation include:
 * total world population, expected by demographers to settle at 10-12 billion
 * the consumption per inhabitant, direct or indirect (mainly of livestock)
 * the total world food production
 * the repartition of this food among the human population
 * uneven population distribution in suitable habitats, leading to fears or the actuality of mass migration
 * non-food resources

Failed predictions
Rash and inaccurate predictions of impending world famine which erred on the side of sensationalism over sober analysis have characterized a great deal of past interest in the subject matter, including by respected scientists. Thomas Malthus, one of the earliest to theorize about overpopulation, wrote in 1798 that the population would grow exponentially while the food supply would only grow arithmetically, failing to take into account technological developments that would provide greater agricultural yield. (Not to mention that food itself is an exponentially growing population.) During the 1960s, Paul Ehrlich predicted massive famine by the 1970s, which didn't happen due to the Green Revolution (which was indeed a revolution in agriculture but is anything but 'green'). His prediction was also based on the assumption that the birth rate in the United States and other Western countries would continue at high Baby Boom levels, and may well have been postponed by the birth rate dropping to near-replacement levels due to the sexual revolution and the related widespread availability of birth control.

In all cases these predictions appear to "fail" because they did not take into account technological and medical advances that delay what seems to be inevitable. One cannot blame them for what they could not know.

Carrying capacity
In 1679, Antoni van Leeuwenhoek (1632 - 1723) estimated that the maximum number of people Earth can support is 13.4 billion. Many more estimates of how many people Earth could support followed. The estimates have varied from 1 billion to 1000 billion. Estimates published in 1994 alone ranged from 3 billion to 44 billion.

Since 1679, there has been no clear increasing or decreasing trend in the estimated upper bounds. The scatter among the estimates increased with the passage of time. This growing divergence is the opposite of the progressive convergence that would ideally occur when a constant of nature is measured. Such estimates deserve the same profound skepticism as population projections. They depend sensitively on assumptions about future natural constraints and human choices. Many authors gave both a low estimate and a high estimate. Considering only the highest number given when an author stated a range, and including all single or point estimates, the median of 65 upper bounds on human population was 12 billion. If the lowest number given is used when an author stated a range of estimates, and all point estimates are included otherwise, the median of 65 estimated bounds on human population was 7.7 billion. This range of low to high medians, 7.7 to 12 billion, is very close to the range of low and high UN projections for 2050: 7.8 to 12.5 billion. A historical survey of estimated limits is no proof that limits lie in this range. It is merely a warning that the human population is entering a zone where limits on the human carrying capacity of Earth have been anticipated and may be encountered.

The Global Footprint Network has calculated the number of planet Earths needed for the entire world to live the lifestyle of each nation at present (2019) consumption levels. A typical number for developed nations is 2.5, a United States lifestyle requires 5 planets, an Indian lifestyle requires 0.7 planets. These are not projections of future carrying capacity accounting for possible efficiency improvements, but they do show the carrying capacity relative to present day consumption patterns.

Solutions
Finding a "solution" to human overpopulation is difficult in that it essentially requires people to reproduce in fewer numbers, something they may be unwilling to do, and any success is likely to be a very gradual process. Greater awareness of and access to contraception around the world would help promote population control, although this is opposed by some cultures and religions, particularly the Roman Catholic Church. There is an international childfree movement that may help curb the problem of overpopulation. More aggressive, though less realistic, is the Voluntary Human Extinction Movement and various antinatalist philosophies, which encourages a complete cessation of human reproduction for either environmental or ethical reasons.

The People's Republic of China's response to its populations problems is the one-child policy, instituted and enforced since 1979. Fearing its economic and societal consequences, however, China started to formally phase out this rule in 2015. With standards of living in China rising rapidly due to miraculous economic growth, it is doubtful that China's birth rate will rise significantly, if at all.

Isaac Asimov took an interest in overpopulation and proposed that homosexuality should be considered a "moral right" since homosexual sex doesn't lead to reproduction, which would help curb overpopulation. While it is occasionally claimed that homosexuality is a response to overpopulation, there's no reason to believe this is true. Also, given the upsurge in surrogate pregnancies, artificial insemination, and various other alternative methods of child production, both present and projected, homosexuality may cease to prevent reproduction.

The demographic transition model holds that as nations transition from low-income, undeveloped nations to high-income, developed nations, their birth rate and death rate both drop. This model posits five stages, and in the fifth and last stage of demographic transition, population levels off and reaches a state of zero or negative population growth. With increased prosperity comes greater autonomy for women in society, better access to family planning and birth control, women entering the workplace and limiting their number of children, and more free flow of information (with the effect of secularizing the society and lessening the influence of religions which promote large families); conversely however, during the middle stages of the demographic transition the death rate drops faster than the birth rate, causing a temporary increase in population. Countries like Japan, much of Europe, and the native inhabitants of the United States are at or near the final stage, and have achieved a state of zero-to-negative population growth without any need for coercive policies such as China's.

Criticism
Critics of measures to reduce overpopulation note that they tend to be levied against the lower-class people of impoverished areas, notoriously with mass sterilization programs enacted in India and Puerto Rico. The British government's poor response to the Irish Potato Famine was justified by Malthusian arguments that Ireland was overpopulated and the only way to save them from the famine was to leave many of the poor Irish to die. The argument that population of poor people causes overconsumption overlooks the fact that developed countries are responsible for the vast majority of environmental destruction; an entire poor family from India or sub-Saharan Africa has a considerably lower impact, on average, than a single American. Furthermore, the majority of environmental damage is caused by large systems such as corporations and governments rather than individual decisions like how much children a family chooses to have. Thus, many people feel that concerns of overpopulation overwhelmingly focus on poor people who are not the cause of environmental problems rather than the powerful institutions that are actually responsible.

People concerned about overpopulation also tend to overwhelmingly pin childbirth responsibility on women while ignoring the mens' role of creating patriarchal systems to control women's reproduction by limiting women's birth control/abortion access and personal autonomy, and indoctrinating the people with traditional natalist culture.

There are reasonable methods of reducing population growth, such as lifting people out of poverty so that they don't have to rely on having more children to support their families, expanding contraception and sex education, and directly educating people on the realities of overpopulation. The fact that overpopulation measures have historically been enacted on the most marginalized of communities should raise eyebrows as to the true motive. There's also the problem that the issue of overpopulation has been used by ecofascists to justify blocking all immigration from nonwhite countries. Some extremists even use such rhetoric to justify outright genocide, with the Christchurch, El Paso, and Buffalo mass shootings all being justified with this kind of ecofascist rhetoric. These examples show how scapegoating a group of people with no real power can have horrifying consequences.

Optimism
(Native) Population growth is falling in almost all First World countries. In extreme cases, the birth rate is well below 2.1, the replacement rate in the case of Japan. The UN has projected that we will likely never reach 11 billion people on Earth. Third World countries are the main source of unsustainable population growth, but as standards of living rise, birth rates tend to drop. Whether the human population growth is curbed enough remains to be seen.

Long known for their high birth rates, South and Southeast Asia have actually ceased their exponential growth. All those tens of millions of jobs that have been going overseas? Well, they've gone to Asia, and more importantly, a lot of those jobs have been going to women. It turns out that a lot of women would rather work for a meager salary for herself than be forced into marriage as a baby-factory. Both India and Bangladesh now have birth rates barely above 2 per woman, and it's still dropping. Vietnam now has a birth rate below 2 per woman, and Thailand a mere 1.5, effectively making the population growth negative longterm. Same with Malaysia, and especially Singapore.

Not just Asia, but Latin America as well. Mexico's birth rate has plummeted to just above 2 per woman and still dropping, and Brazil is well below 2 per woman. Colombia, Argentina, Chile, also below 2. Even in Africa birth rates are falling, although much more slowly.

A lot can happen in 40 years.