The logic sounds impeccable: if the number of people in the world threatens to outstrip the planet’s resources, then stemming population growth would solve the problem.

That line of thinking has come to be known by its critics as the Malthusian fallacy, named after the 19th century English writer Thomas Malthus who argued that human population would inevitably exceed the capacity of the environment to sustain it.

The concern in Malthus’s day was that population would outstrip agricultural production. But his theory overlooked the prospect of technological advances that would help to meet that challenge.

In more recent times, the threat of human-generated climate change has prompted some to reach for neo-Malthusian solutions to what is widely viewed at the most severe challenge facing humankind.

Confronted with growing evidence of the impact of global warming, some young couples in the West are even choosing not to have children rather than add to the climate burden.

These so-called Birth Strikers were apparently inspired by US Congresswoman Alexandria Ocasio-Cortez when she said: “It is basically a scientific consensus that the lives of our children are going to be very difficult, and it does lead young people to have a legitimate question: is it OK to still have children?”

It is one of a range of decisions, along with not eating meat and abandoning air travel, that have been popularized with the rise of the Extinction Rebellion movement.

These might seem extreme solutions. However, the role of population size in the climate debate has also won support within the scientific community.

A decade ago, a scientific study in the United States on the relationship between population growth and global warming calculated that the “carbon legacy” of just one child amounted to 20 times what an individual would save by driving an efficient car, recycling and using energy-efficient appliances and light bulbs.

“Clearly, the potential savings from reduced reproduction are huge compared to the savings that can be achieved by changes in lifestyle,” the study by scientists as Oregon State University concluded.

More recently, a widely peer=endorsed article in this month’s edition of journal BioScience on the topic of the climate emergency argued that the present world population increase of more than 200,000 a day must be stabilized and, ideally, gradually reduced.

A contrary argument is that artificially slowing world population growth would shrink demand for a variety of staples, inevitably leading to a slowdown in the world economy and to global recession.

Advocates of controlling population have also been criticized on the grounds that the energy consumption of people in the developed world, where birth rates are already relatively low, far outstrips that of those in the developing world.

Contrary to Malthus’s predictions, the wealthiest countries with the greatest food security have the lowest fertility rates, whereas the most food-insecure countries have the highest fertility rates.

The critics see the focus on population as another case of the rich West imposing solutions on those who are relatively poor.

A report on the recent BioScience findings in the MIT Technology Review noted that rich nations generally already have fl at or declining birth rates, so the proposal largely seemed directed at fast-growing developing nations in Africa and Asia.

It quoted a Twitter posting from Arvind Ravikumar, a United State-based energy engineer, who commented: “A bunch of white people in the developed world saying population should be reduced is the definition of an imperialist framing.”

Such comments reflect concerns that provoked a much older debate in which the arguments of Malthus, known by contemporaries as a gentle and kindly Christian clergyman, were used to promote eugenics and justify policies of sterilization, invariably aimed at the poor.

It was an era in which the poor were seen as broadly responsible for their own fate through their alleged stupidity and laxity. Allowing them to breed faster than their betters, so the arguments of the day went, would be “injurious to the race”.

Happily, modern science has done away with such distinctions based on false theories of ethnicity and social background.

Rather what modern history has shown is that as societies become more prosperous, people will tend to have smaller families. Advances in medicine mean that more babies are surviving their early months and, at the other end of the scale, people are living longer.

More efficient agriculture means that the planet can now support many more people than would have been thought possible in Malthus’s day.

However, climate change has now replaced famine as the existential threat that stalks the world. Science now faces the challenge of coming up with solutions-and governments with the challenge of implementing them-to combat this new threat.

To adopt the buzzword of every contemporary policymaker, population growth has to be “sustainable”. In that context, everyone has an obligation to make sure they limit their carbon footprint, perhaps without taking the extreme position of ceasing to breed.

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