Mostly, fisherwomen catch catfish in water. They slowly wade through river shallows and fens, feeling the silt with their bare toes for catfish burrows to learn where to set reed traps, which are domed like birdcages, like lanterns. They curl the fish head-to-tail into elegant teardrops and arrange them on giant grills. The women sit before the smoldering coals for hours, naked from the waist up, sweating, a small child on the breast, knees spraddled inside their kaleidoscopic pagnes, river goddesses. Later, they take the smoked fish to the produce market in wicker baskets.

In Djenné, a Niger Delta town in central Mali, you can buy a smoked catfish for between a dime and a half-dollar, depending on the size. Its obovate heft is still warm from the gridiron, its skin stripe-charred golden and black; you want to caress it. Later, your hands smell like chipotle. You imagine its journey, from the Cretaceous lakes to a fisherwoman’s trap, to the hot grill she guards between her thighs, to the Sudanic clay walls of this medieval market town, to your own hearth. You check the guts for worms and cook the fish whole in a spicy sauce. Served over rice, one catfish will feed an entire family, and there may even be leftovers. Adults use their pinkies to pry the frilled cheeks from beneath the sharp panzer gills. The cheeks are the sweetest.

Catfish are fatty, full of protein and vitamin B-12 essential for brain function, the nervous system and the formation of red blood cells. If Bomel Diakayaté—Oumarou’s daughter—ate catfish, perhaps she would have had enough milk in the shriveled envelopes of her breasts to nurse her baby daughter, Mayrama, to fullness. Perhaps then Mayrama, who at 12 months weighed less than my son weighed at birth, would not have had to be rushed to the grimy Djenné hospital at the last possible moment, pinned with inconceivably thin catheters, resuscitated from the brink.

But there was the matter of webbed hands.

“Probably food taboos … exist in one form or another in every society on Earth, for it is a fact that perhaps nowhere in the world, a people, a tribe, or an ethnic group, makes use of the full potential of edible items in its surroundings,” the ethnobiologist Victor Benno Meyer-Rochow writes in his study Food Taboos: Their Origins and Purposes. What are they for? In some societies, suggests the anthropologist David R. McDonald, a taboo seems designed to be “a primitive environmental protection agency,” to protect species from extirpation and stave off ecological crises. In others, it may serve to dictate class divisions and subordination, keeping one sector of the society dominant over the rest, predictably maintaining a dependable—if unfair—social order.

Many food bans appear to defy scientific reasoning, evoke magic. Take my Djennénke friend Amadou Gano, whose ancestors were nomadic herders like the Diakayatés. There is no animal Gano would not eat. He has eaten donkey and dog. He has eaten pig! All of these are haram, forbidden by Islam, and Gano is Muslim. I don’t know how he gets away with such a sinful diet. Maybe the prayers he utters each time he leaves or enters a house or a hut, begins a new task or sets out on a journey—even to the market to buy some cigarettes, which are haram as well—absolve him. But he cannot eat anything, especially not meat, while walking. A marabout, a holy man, told him this. The ban is the result of a curse of some kind, perhaps a blood feud, who knows how old. It extends only to the males in his family: They must eat sitting down. (Eating aboard a moving bus is okay.) What happens if Gano eats on the go? He would not say. The repercussion is so awful it is unspeakable.

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What we choose to include in our diet and what we disallow describes a story, a history. Like the Fulani catfish ban, food taboos can be maps tracing our very specific connections to the Pleistocene forefathers on the African savannah, ritual expressions of our cultural identities. They bind us, make us belong: We observe kashrut, or halal food laws, or Lent because that is what our ancestors did.

Food taboos are also borders meant to keep things away—poor health, evil eye, outsiders, loneliness. Malnutrition, on the other hand, is a void, an opening. It weakens the body, invites illness, death. But what happens when an ancient rite meets a new, modern problem: a rapidly drying continent? The drastic changes in the world’s climate scramble this dichotomy, leave families like Oumarou’s teetering between the two boundaries of diet: the customary, internal—and the circumstantial, imposed by the thirsty, hungry world. Today’s Anthropocene age is subverting the basics of identity, and the cultural framework we rely on to buoy us at times of hardship is metamorphosing into a conduit for more hardship instead.

Left: Mayrama Diakayaté, who had to be rushed to the hospital shortly after birth because of her mother's extreme anemia. Center: A “nutrition tree” at a clinic in Mali. Right: Oumarou Diakayaté with his grandson | Anna Badkhen

In an analysis it published this winter, the USAID Office of Food for Peace cites “lack of knowledge of proper nutrition” and “taboos in some ethnic groups that discourage the consumption of eggs or meat” as major causes of malnutrition in Mali. In a policy manual for health workers in West Africa, the Dutch nutrition expert Maja Slingerland points out that “many food taboos are more stringent for pregnant and lactating women, just at the time when their nutritional requirements are greatest.” (Many Sahelian mothers throw away colostrum—the thick, yellow breast milk that appears after delivery and is packed with antibodies essential for a newborn—because they consider it unclean, dangerous for the baby.) The Nigerian food scientists Elias C. Onuorah and Jerome Ayokunle Ayo urge that “agencies and individuals effectively fight these food taboos” to combat malnutrition.

If it shows no respect for dietary restrictions, at least the modern development community recognizes them as a factor. This wasn’t always the case. In the 1970s and ’80s, well-meaning Norwegian donors poured millions of dollars into a state-of-the-art freezer plant, modern roads, fiberglass boats, nets and an educational program to convert some 20,000 hungry Turkana pastoralists into fishermen. The Norwegians didn’t bother to learn that the East African nomads did not eat fish. Diverted from animal husbandry, thousands of Turkana who participated in the project lost their herds; their children became sick from disease that festered in standing water—while the freezer plant turned out too costly to operate. Then severe droughts dried out a chunk of the lake, the former nomads became dependent on food aid and the flopped project became a symbol of mindless aid efforts in Africa.

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How do you “effectively fight” ancient food practices in the bush of ghosts? Western Sahel teems with genie and malicious mermen. It sprouts plants that possess curative powers if collected on a Thursday, the pre-Islamic day of the spirits. It is gridded with boundaries invisible and unutterable. It is the birthplace of magical realism. Navigating its interdictions requires both an open mind and mindfulness, in carefully weighed proportions.

Maybe you just outwait them.

“We don’t see life in terms of time; we see life in terms of cycles: day-night, rain-dry,” Ibrahim Togola, an environmental engineer in Bamako, told me. “Now all the cycles are confused.” So are the people who inhabit them. All around Oumarou, new ways abrade the world. The Diakayaté young abandon life in the withering bush, move to cities. A weathering away of everything is taking place, a kind of erosion in which Oumarou’s proud custom looks anachronistic, foolish. Rising temperatures and sand wring dry rivers. Acres of deforested riverbank dry out and blow away or collapse into the water. Fish, too, run off schedule. So what if some catfish can survive in moist mud? They cannot hide there forever. Fisherwomen say their catch is shrinking. Last year, the International Fund for Agricultural Development ranked Mali’s fisheries and aquaculture the world’s sixth most-vulnerable to the impacts of climate change.

Day after day, on the backdrop of chronic hunger, Oumarou Diakayaté sits stock-still on a reed mat and divines the unending Sahelian horizon for rain in the tradition of his ancestors. A few dozen feet away, in a fen, forbidden catfish may be burrowing, waiting for the same rain. In Oumarou’s mind, by refusing catfish he preserves the integrity of his milking hands, the future of his family: Like any diet, a food taboo is a mechanism of control. But, of course, he preserves nothing.

Together and apart, they wait. I think: Here they are, man and fish. Two ways of being in the world that once seemed eternal and now are equally precarious, out of water. Species kept separate for millennia by magical thinking, linked on their dehydrated plateau in irreversible ways they cannot imagine, cannot avert.