How Zero Population Growth Works

Over the past 110 years – a blink of the eye in human history – the world population has exploded from 1.6 billion to 7.2 billion [source: Graf and Bremner]. This exponential growth has many causes, most of them positive and directly related to improvements in health care [sources: CDC, Wattenberg, WHO]:

Still, the vast gains humanity has made in terms of health, economic security and human rights have not been distributed equally among the world's 7.2 billion inhabitants [sources: FAO, UN]:

Global population growth also puts a strain on natural resources like clean water and forests [sources: WHO, WWF].

In 2014, more than half of the world's population lived in cities [source: UN]. While cities can provide improved economic opportunities for people in developing countries, they are also home to slums and sweatshops. In the poorest nations, more than half of city-dwellers live in slums with limited or no access to clean water, sanitation or permanent shelter, let alone education or health care. In sub-Saharan Africa, 61.7 percent of the urban population lives in slums. The United Nations predicts that almost all of future population growth will happen in cities.

Even if Ehrlich's original predictions were wrong, there are clearly regions of the world in which too many people are struggling to survive on too few resources. Next we'll look at some of the solutions to overpopulation proposed by the zero population growth movement.

Zero Population Growth, the organization cofounded by Paul Ehrlich in 1968, is now called Population Connection. Population Connection is deeply concerned about the threat of unfettered population growth to the environment, human rights, and the health and safety of women and girls.

For Population Connection, the most effective solution to dangerous levels of population growth is to increase women's access to modern methods of contraception. According to statistics collected by the organization, there are 222 million women in the developing world who have an "unmet need for family planning" [source: Population Connection].

Population Connection defines this "unmet need" as women who are sexually active, fertile, and not using contraception, but who don't want a child in the next two years. Population Connection believes that simply by eliminating unintended pregnancies we could reduce population growth by 33 million unplanned births a year.

Improving access to contraception is only part of the solution to overpopulation. Education and family planning counseling is also key, especially in developing countries.

In Uganda, for example, a third of married women report an unmet need for family planning. Relatively few of these women – only 8 percent those surveyed – cited lack of access as their top reason for not using contraception. Instead, they expressed fears about side effects; confusion over the need for contraception after birth; opposition from their husbands and others; and a belief that you don't need to use contraception if you have sex infrequently [source: Megquier]. Similar results are reported for other countries in the developing world.

A woman's right to take control of her own fertility is closely tied to other human rights. Women who have access to better education, better health care, and better employment opportunities have fewer children on average than women who don't enjoy those same rights.

Despite its good intentions, the zero population growth movement has many vocal and passionate critics. Keep reading to hear their side of the population growth story.

Some of the loudest critics of the zero population growth movement are critics of Paul Ehrlich himself.

"If I were a gambler," Ehrlich wrote in "The Population Bomb," "I would take even money that England will not exist in the year 2000." He made similar predictions about India, which would dissolve in a slew of food shortages, disease and riots [source: Chivers].

Something that Ehrlich failed to foresee was the "Green Revolution" in agriculture. While Ehrlich was making his doomsday predictions, an international consortium of plant scientists began breeding higher-yielding varieties of rice that would thrive in difficult growing conditions. These seeds, in combination with widespread use of chemical fertilizer and modern growing practices, led to vastly larger harvests in the developing world [source: IFPRI].

Critics of Ehrlich and the zero population growth movement use the example of the Green Revolution to assert that people – far from being "parasites" on the planet – are one of its greatest resources. People create and innovate, designing technologies and systems that have increased overall quality of life since 1968, even as the global population doubled.

Other critics of zero population growth believe that low birth rates are bad for the economy. If fewer people are born each year, then a nation's population gets progressively older on average. The fear is that fewer working-age people will result in less consumption of goods and services, slowing the economy. Also, without enough young working people, there won't be enough tax revenue to support social programs for the elderly.

Another criticism of the zero population growth movement is that countries with lower fertility rates actually do more damage to the environment. The two greatest producers of climate-changing greenhouse gasses are China and the United States, with relatively low fertility rates of 1.7 babies per woman and 1.9 babies per woman respectively [sources: UCS, World Bank]. Carbon emissions closely track per-capita income levels, not population growth rates.

As of 2015, population growth worldwide is slowing significantly.

More than 70 countries are now categorized as "low fertility" with rates of two babies per woman or less. Still, more than 60 "high-fertility" countries (i.e., more than three children per woman), mostly nations in Africa and Asia, are expected to make great economic gains over the coming decades [source: UN]. As these growing populations develop into global consumers, they will pose new threats to the environment.

When Paul Ehrlich founded Zero Population Growth, the belief was that world population would continue to grow exponentially, greatly outpacing our ability to feed ourselves. The modern population growth movement, led by groups like Population Connection, Population Institute and the Population Reference Bureau, place a greater emphasis on women's reproductive rights and improving access to family planning resources.

The critics may scoff at Ehrlich, but by dropping his "bomb" of wild predictions, he launched a movement whose very goal was to prove himself wrong.