A reader writes:

I once had the pleasure of hiking in Yellowstone National Park with USGS wildlife biologist Dave Mattson, a man who, thanks to his job, may have walked more of the nation's public lands than anyone else. He took us too a spot along the Yellowstone River where grizzly bears eat volcanic dirt, especially in the spring when they come out of hibernation. There are numerous theories as to why they do so, but, as with pregnant women, there is no surefire explanation. The soil they eat - and they seek out a specific type - is high in potassium. An abstract of a paper co-authored by Mattson is here. According to this grizzly bear blog:

The researchers concluded the soil consumption may have several functions. Like ungulates, grizzlies may eat earth to detoxify secondary compounds present in the foliage they consume and to supplement their diet with potassium. In the areas where grizzlies ingested soil, the earth has very high in potassium, magnesium and sulphur. The authors also suggest that that by consuming these soils, the bears may prevent diarrhea by helping to get rid of some parasites and bacteria in the alimentary tract.

The image of those bears seeking out and eating this special earth reminded me of human geophagy, most notably Rebeca in Gabriel Garcia Marquez's "100 Years of Solitude and the pilgrims who eat the "holy dirt" at El Santuario de Chimayo in New Mexico. In reference to Chimayo, the CDC says:

Eating dirt, then, rather than being abnormal, may be an evolutionary adaptation acquired over millennia of productive and not-so-productive interactions with bacteriaan adaptation that enhances fetal immunity and increases calcium, eliminates gastric upset, detoxifies some plant and animal toxins, and perhaps boosts mothers’ immunity at times when the hormones of pregnancy (13), factors produced by the fetus (14), changes in the complement system, replacement of MHC class I antigens in the trophoblast (15), and who knows what else suppress the mother’s natural immunologic desire to destroy her fetusa miracle, nearly.

Another reader sends in a passage from "One Hundred Years of Solitude":

On rainy afternoons, embroidering with a group of friends on the begonia porch, she would lose the thread of the conversation and a tear of nostalgia would salt her palate when she saw the strips of damp earth and the piles of mud that the earthworms had pushed up in the garden. Those secret tastes, defeated in the past by oranges and rhubarb, broke out into an irrepressible urge when she began to weep. She went back to eating earth.

The first time she did it almost out of curiosity, sure that the bad taste would be the best cure for the temptation. And, in fact, she could not bear the earth in her mouth. But she persevered, overcome by the growing anxiety, and little by little she was getting back her ancestral appetite, the taste of primary minerals, the unbridled satisfaction of what was the original food. She would put handfuls of earth in her pockets, and ate them in small bits without being seen, with a confused feeling of pleasure and rage, as she instructed her girl friends in the most difficult needlepoint and spoke about other men, who did not deserve the sacrifice of having one eat the whitewash on the walls because of them.

The handfuls of earth made the only man who deserved that show of degradation  less remote and more certain, as if the ground that he walked on with his fine patent leather boots in another part of the world were transmitting to her the weight and the temperature of his blood in a mineral savor that left a harsh aftertaste in her mouth and a sediment of peace in her heart.

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