“Father once measured some thirty grown Yahgan men. The tallest of them was five feet five inches and the shortest just under four feet eight, the average height being five feet two and a quarter inches. Yet, in spite of their short statues, they were strong, and FitzRoy says frankly that he forbade his sailors to wrestle with the natives, who, being the strongest, would learn to despise the white men. The Yahgan women were short and fat, with tapering limbs and little hands and feet.”
This from a book I’ve been reading in fits and starts, Uttermost Part of the Earth: A history of Tierra Del Fuego and the Fuegians (p.62). It’s a memoir by E. Lucas Bridges, who was born in 1874 in Tierra Del Fuego at the southernmost tip of South America. Bridges was the son of the very first missionaries to the region. The book was published in 1948.
So why a black swan? The italics in the quote are mine. The women, writes Bridges, were fat, and yet the diet was virtually all animal products: fish, otter, seal, guanaco, foxes, and birds. If sugar and refined carbohydrates make us fat, as I’ve argued in my books, shouldn’t these women have been lean? Is that a black swan, the refutation of the hypothesis? I would say no, but it’s an interesting discussion (I hope).
One possibility could be that the significant adiposity in these women is an evolutionary adaptation to the climate and lifestyle. As Bridges details, these shore-dwelling natives lived in an inhospitable climate and yet spent much of their lives mostly naked and cold. They had few animal skins in which to clothe themselves. Their word for a poor person, he says, was api tupan, meaning “body only,” and “many of the young indians qualified for the epithet.” Moreover, the tribe lived off canoes and the fish they caught, and the women did the fishing, swimming in the frigid waters. “The women were always good swimmers,” Bridges writes, “but it was a very rare thing to find a male Yahgan who could swim… They learn to swim in infancy, and were taken out by their mothers in order to get them used to it. In winter… a baby girl out with her mother would sometimes make pick-a-back swimming difficult by climbing onto her parent’s head to escape the cold water and frozen kelp.”
Maybe, like they do for marine mammals, thick layers of fat served as insulation for these women, an evolutionary advantage? Maybe the fat provided buoyancy. These explanations assume that these people had been around long enough in this particular environment for this kind of evolutionary adaptation to manifest itself in the population.
This is the problem with interpreting any causality from these kinds of observations. Infinite possible explanations exist. So let’s ask instead a simpler question, the black swan question: does this observation refute the alternative hypothesis, that obesity is a hormonal/regulatory disorder triggered by the sugars and refined, easily digestible carbohydrates in our diets. Or in simpler terms, that these carbohydrates are fattening? Or an implication of the hypothesis argued in The Case Against Sugar: add sugar, in particular, to any traditional diet and one result eventually is an epidemic of obesity?
Since these women were already fat — and we don’t know if that meant obese as we think about it today or just, let’s say, usefully fat, perhaps a little zaftig rather than exceedingly thin as we’d describe it today — the hypothesis would predict that they would get fatter still and clearly obese as they are westernized. But this observation dates to the 1870s, at the very cusp of the process of westernization. As such it says nothing about what happens after. And the hormonal/regulatory hypothesis itself (or the carbohydrate insulin model, which is a subset of the theme) makes no prediction about whether these women would have been perceived as fat prior to adding these refined carbohydrates to their diet. It merely predicts that they would have gotten fatter and diabetic with the introduction of these western foods, and it’s quite likely that happened in this population, even if we can’t say it was causal. Obesity and diabetes are as common today in this area of Chile as in many areas of the world, so maybe that’s the sugar and refined carbs.
The observation of significant adiposity in these native women is thought-provoking. I do not think it’s a black swan.