SPEAKER_04: Amazing, fascinating stories of inventions, ideas and innovations. Yes, this is the podcast about the things that have helped to shape our lives. Podcasts from the BBC World Service are supported by advertising.
SPEAKER_02: 50 things that made the modern economy with Tim Harford.
SPEAKER_01: In 1981, in Nampula, Mozambique, a young Swedish doctor, Hans Rosling, was puzzled. More and more people were coming to his clinic, suffering from paralysis in their legs. Could it be an outbreak of polio? No, the symptoms were not in any textbook. With Mozambique slipping into a civil war, might it be chemical weapons? He packed his wife and young children off to safety and continued his investigations. The resolution of the mystery sheds light not just on paralysis of the legs, but on one of the biggest economic questions. Why do humans have an economy at all? Let's return to Mozambique in due course. First, an outback adventure. In 1860, Robert Burke and William Wills led the first European expedition across the interior
SPEAKER_01: of Australia. Burke, Wills and their companion John King ran out of food on the return journey. They became stranded at a stream called Cooper's Creek. This is what William Wills wrote.
SPEAKER_00: We have been unable to leave the creek. Both camels are dead and our provisions are done. We are trying to live the best way we can, like the blacks, but find it hard work.
SPEAKER_01: By the blacks, Wills meant the local Yandrewandra people, who seemed to thrive despite conditions that were proving too tough for Burke, Wills and King. The Yandrewandra gave the explorers cakes made from the crushed seed pods of a clover-like fern called nardu. But later, Burke fell out with them and unwisely drove them away by firing his pistol. But perhaps Burke, Wills and King had already learned enough to survive. They found fresh nardu and decided to make their own cakes. At first, all seemed well. The nardu cakes satisfied their appetites, yet they felt ever weaker. Within a week, he and Burke were dead. It turns out that safely preparing nardu is a complex process. Nardu is packed with an enzyme called thiaminase. Thiaminase breaks down the body's supply of vitamin B1, preventing it using the nutrients in food. Burke, Wills and King were full but starving. The Yandrewandra roasted the nardu spores, ground the flour with water and exposed the cakes to ash, each step making the thiaminase less toxic. It is not something one learns to do at a glance. Barely alive, John King threw himself on the mercy of the Yandrewandra. They took pity on him, keeping him alive until European help arrived months later. As a foodstuff, nardu is a curiosity. The same cannot be said of cassava roots, which are a vital source of calories in many tropical countries, particularly for subsistence farmers in Africa. But cassava is toxic, like nardu. And, like nardu, it requires a tedious and complex preparation ritual to make it safe. The cassava root will otherwise release hydrogen cyanide. What makes cassava particularly treacherous is that while some processing will reduce the bitter taste and the risk of immediate cyanide poisoning, only the full time-consuming ritual can guarantee that you won't be slowly poisoned, producing a condition called conzo, with symptoms including sudden paralysis of the legs. An epidemiologist, Julie Cliff, eventually figured out that that's what had happened to the patients at Hans Rosling's clinic in Mozambique. Their meals of cassava had been incompletely processed. Already hungry and malnourished, they couldn't wait long enough to make the cassava safe. Toxic plants are everywhere. Often, simply cooking makes them edible. But how does anyone learn the elaborate preparation needed for cassava or nardu? No single person does, according to Joseph Henrich, an evolutionary biologist. He says this knowledge is cultural. Our cultures evolve through a process of trial and error, analogous to evolution in biological species. Like biological evolution, cultural evolution can, given enough time, produce impressively sophisticated results. Somebody stumbles on one step that seems to make cassava less risky, that spreads, and another step is discovered. Over time, complex rituals can evolve, each slightly more effective than the last. In the Amazon, where humans have eaten cassava for thousands of years, tribes have learned the many steps needed to detoxify it completely. Scrape, grate, wash, boil the liquid, leave the solid to stand for two days, then bake. Ask why they do this, and they won't mention hydrogen cyanide. They'll simply say, this is our culture. In Africa, cassava was introduced only in the 17th century. It didn't come with an instruction manual. Cyanide poisoning is still an occasional problem. People take shortcuts because cultural learning is still incomplete. Henrich says that cultural evolution is often much smarter than we are. Whether it's constructing an igloo, hunting an antelope, lighting a fire, making a longbow, or processing cassava, we learn not by understanding from first principles, but by imitating. One study challenged participants to place weights on the spokes of a wheel to maximise the speed at which it rolled down a slope. Each person's best effort would be passed to the next person. Because they benefited from earlier experiments, later participants did much better. Yet, when asked, they showed no sign of actually understanding why some wheels rolled faster than others. Further studies show that the verb to ape, meaning to copy, is ironically misplaced. The only ape with the instinct to imitate is us. Tests reveal two and a half year old chimps and humans have similar mental capacities, unless the challenge is to learn by copying someone. The toddlers are vastly better at copying than the chimps. And humans ritualistically copy in a way that chimps do not. Psychologists call this over-imitation. It may seem like the chimps are the smart ones here, but if you're processing cassava roots, over-imitation is exactly what you should be doing. If Henrich is right, human civilisation is based less on raw intelligence than on a highly developed ability to learn from each other. Over the generations, our ancestors accumulated useful ideas by trial and error, and the next generation simply copied them. Yes, now we have the scientific method, but we shouldn't look down on the kind of collective intelligence that saved John King's life. It's that that made civilisation and the economy possible.
SPEAKER_02: The mystery of cassava processing was drawn to our attention by Joseph Henrich's book, The Secret of Our Success. For a full list of our sources, please see bbcworldservice.com slash 50things.
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