Humans are natural problem solvers, thriving on challenges that drive our growth and maturity. But while we excel at anticipating the immediate consequences of our decisions or actions, we often struggle to foresee second-order effects—the consequences of the consequences. Many seemingly reasonable solutions, such as the use of DDT to combat insects, have had disastrous unintended consequences, encapsulated in the old adage that the road to hell is paved with good intentions. Here we examine well-intentioned solutions aimed at improving human life or the environment that ultimately went disastrously wrong.
WHEN PEST CONTROL SOLUTIONS BACKFIRE
When the Black Death struck London in early 1665, panicked authorities ordered the culling of dogs and cats, believing them to be the main carriers of the disease. According to Daniel Defoe’s A Journal of the Plague Year, “forty thousand dogs, and five times as many cats” were destroyed. It is now understood that the plague was caused by the bacterium Yersinia pestis, which was transmitted to humans through the bites of infected fleas living on rats. By eliminating the rodents’ predators, the authorities inadvertently allowed them to thrive, making it easier for the disease to spread. Up to 100,000 people perished in the Great London Plague.
During British rule in India, the authorities wanted to reduce the number of venomous cobras in Delhi and offered a bounty for every dead cobra. While this strategy worked at first, people soon realised that it was easier to breed cobras than to catch them in the wild. When the government became aware of this, they scrapped the scheme, and the cobra breeders released their snakes, adding to the wild cobra population. Although likely apocryphal, this story inspired the term “cobra effect.” A similar but historically true event occurred in 1902 in what is now Hanoi, Vietnam, when French colonial authorities tried to control the rat population with a bounty scheme that paid 1¢ per rat tail. Soon tailless rats began appearing everywhere. Rat catchers would cut off their tails and release them back into the sewers to breed more rats, thereby ensuring a future income.
China’s Chairman Mao, who ruled from 1949 to 1976, was many things, but a lover of nature wasn’t one of them. His slogan “Man Must Conquer Nature” became a rallying cry, culminating in the “Four Pests Campaign” during the Great Leap Forward in 1958, which targeted flies, mosquitoes, rats and sparrows. Birds were included because they eat grain, but no one considered that they also consume huge quantities of insects. After farmers killed hundreds of millions of sparrows, locust populations grew exponentially, exacerbating ecological problems caused by deforestation and the misuse of pesticides. The ensuing Great Chinese Famine killed up to 45 million people.
Invasive species are perhaps the quintessential example of negative unintended consequences, and the cane toad is perhaps the best known. Introduced to eastern Australia in 1935 to control the native cane beetle that was damaging sugarcane crops, these large South American toads—whose toxic skin can kill many animals—were intended to be an environmentally friendly alternative to pesticides. However, the cane toad failed to reduce beetle numbers but had a devastating impact on Australia’s biodiversity. For more than 80 years, the toad has spread relentlessly across the country, leaving a trail of ecological devastation in its wake.
WHEN PUBLIC POLICIES ACCOMPLISH THE REVERSE
Over the past century, countries such as Canada and the US have pursued a popular policy of quickly extinguishing all wildfires, investing billions in manpower, firefighting equipment and fire safety education. This strategy has unintentionally left forests choked with brush and other dry fuels, leading to bigger, hotter and more destructive fires.
Since 2014, there has been a moratorium on recreational hunting in Spain’s national parks, a decision widely supported by the public. However, hunters had played a crucial role in controlling populations of ungulates such as ibex, deer and wild boar. With hunting banned and natural predators such as wolves absent, ungulate populations have soared and park authorities are struggling to control their numbers. The result has been environmental damage, reduced biodiversity and an increase in human-wildlife conflict.
MITIGATING UNINTENDED CONSEQUENCES
These cautionary tales should give us pause as we consider how to tackle challenges such as climate change, sustainable energy or artificial intelligence. Decision-makers who overemphasise the first-order consequences of their decisions and actions, while ignoring the second- and third-order effects, risk seeing their plans backfire. But given the complexity and interconnectedness of modern civilisation and the accelerating pace of change, can the human mind even grasp all the potential ramifications of an action?
Experts recommend that we train ourselves to think in “what if” scenarios and that organisations establish a formal framework and process for assessing second-order and knock-on effects. Dealing with unintended consequences requires humility and a willingness to embrace uncertainty; we need to take the time to investigate what we don’t know and actively seek alternative options. The best approach is a nimble one, where no decision is set in stone and a rapid change of course is possible if unintended consequences arise. Above all, we must remember that while we can’t always make things better, we should strive to avoid making them worse.
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