>The bet was on, and it was over the fate of humanity. On one side was the Stanford biologist Paul R. Ehrlich. In his 1968 best seller, The Population Bomb, Ehrlich insisted that it was too late to prevent a doomsday apocalypse resulting from overpopulation. Resource shortages would cause hundreds of millions of starvation deaths within a decade. It was cold, hard math: The human population was growing exponentially; the food supply was not. Ehrlich was an accomplished butterfly specialist. He knew that nature did not regulate animal populations delicately. Populations exploded, blowing past the available resources, and then crashed.
>In his book, Ehrlich played out hypothetical scenarios that represented “the kinds of disasters that will occur.” In the worst-case scenario, famine rages across the planet. Russia, China, and the United States are dragged into nuclear war, and the resulting environmental degradation soon extinguishes the human race. In the “cheerful” scenario, population controls begin. Famine spreads, and countries teeter, but the major death wave ends in the mid-1980s. Only half a billion or so people die of starvation. “I challenge you to create one more optimistic,” Ehrlich wrote, adding that he would not count scenarios involving benevolent aliens bearing care packages.The economist Julian Simon took up Ehrlich’s challenge. Technology—water-control techniques, hybridized seeds, management strategies—had revolutionized agriculture, and global crop yields were increasing. To Simon, more people meant more good ideas about how to achieve a sustainable future. So he proposed a wager. Ehrlich could choose five metals that he expected to become more expensive as resources were depleted and chaos ensued over the next decade. Both men agreed that commodity prices were a fine proxy for the effects of population growth, and they set the stakes at $1,000 worth of Ehrlich’s five metals. If, 10 years hence, prices had gone down, Ehrlich would have to pay the difference in value to Simon. If prices went up, Simon would be on the hook for the difference. The bet was made official in 1980.
>Ehrlich’s starvation predictions were almost comically bad. And yet, the very same year he conceded the bet, Ehrlich doubled down in another book, with another prediction that would prove untrue: Sure, his timeline had been a little off, he wrote, but “now the population bomb has detonated.” Despite one erroneous prediction after another, Ehrlich amassed an enormous following and received prestigious awards. Simon, meanwhile, became a standard-bearer for scholars who felt that Ehrlich had ignored economic principles. The kind of excessive regulations Ehrlich advocated, the Simon camp argued, would quell the very innovation that had delivered humanity from catastrophe. Both men became luminaries in their respective domains. Both were mistaken.
>The result: The experts were, by and large, horrific forecasters. Their areas of specialty, years of experience, and (for some) access to classified information made no difference. They were bad at short-term forecasting and bad at long-term forecasting. They were bad at forecasting in every domain. When experts declared that future events were impossible or nearly impossible, 15 percent of them occurred nonetheless. When they declared events to be a sure thing, more than one-quarter of them failed to transpire. As the Danish proverb warns, “It is difficult to make predictions, especially about the future.”
>Even faced with their results, many experts never admitted systematic flaws in their judgment. When they missed wildly, it was a near miss; if just one little thing had gone differently, they would have nailed it. “There is often a curiously inverse relationship,” Tetlock concluded, “between how well forecasters thought they were doing and how well they did.”Early predictions in Tetlock’s research pertained to the future of the Soviet Union. Some experts (usually liberals) saw Mikhail Gorbachev as an earnest reformer who would be able to change the Soviet Union and keep it intact for a while, and other experts (usually conservatives) felt that the Soviet Union was immune to reform and losing legitimacy. Both sides were partly right and partly wrong. Gorbachev did bring real reform, opening the Soviet Union to the world and empowering citizens. But those reforms unleashed pent-up forces in the republics outside Russia, where the system had lost legitimacy. The forces blew the Soviet Union apart. Both camps of experts were blindsided by the swift demise of the U.S.S.R.One subgroup of scholars, however, did manage to see more of what was coming. Unlike Ehrlich and Simon, they were not vested in a single discipline. They took from each argument and integrated apparently contradictory worldviews. They agreed that Gorbachev was a real reformer and that the Soviet Union had lost legitimacy outside Russia. A few of those integrators saw that the end of the Soviet Union was close at hand and that real reforms would be the catalyst.The integrators outperformed their colleagues in pretty much every way, but especially trounced them on long-term predictions. Eventually, Tetlock bestowed nicknames (borrowed from the philosopher Isaiah Berlin) on the experts he’d observed: The highly specialized hedgehogs knew “one big thing,” while the integrator foxes knew “many little things.”Hedgehogs are deeply and tightly focused. Some have spent their career studying one problem. Like Ehrlich and Simon, they fashion tidy theories of how the world works based on observations through the single lens of their specialty. Foxes, meanwhile, “draw from an eclectic array of traditions, and accept ambiguity and contradiction,” Tetlock wrote. Where hedgehogs represent narrowness, foxes embody breadth.Incredibly, the hedgehogs performed especially poorly on long-term predictions within their specialty. They got worse as they accumulated experience and credentials in their field. The more information they had to work with, the more easily they could fit any story into their worldview.
>In Tetlock’s 20-year study, both the broad foxes and the narrow hedgehogs were quick to let a successful prediction reinforce their beliefs. But when an outcome took them by surprise, foxes were much more likely to adjust their ideas. Hedgehogs barely budged. Some made authoritative predictions that turned out to be wildly wrong—then updated their theories in the wrong direction. They became even more convinced of the original beliefs that had led them astray. The best forecasters, by contrast, view their own ideas as hypotheses in need of testing. If they make a bet and lose, they embrace the logic of a loss just as they would the reinforcement of a win. This is called, in a word, learning.