Pygmies, the most well-known group of diminutive humans, whose men on average grow to a maximum of five feet tall and their women about a half foot shorter, were thought to be endowed with their characteristic small body sizes due to poor nutrition and environmental conditions. But the theories did not hold up, given that these populations—primarily hunter-gatherers—are found mostly in Africa but also in Southeast Asia and central South America, and thereby are exposed to varying climates and diets. Further, other populations who live under conditions of low sustenance, such as Kenya's Masai tribes, are among the world's tallest people. So what could account for these pockets of people who grow so small? According to University of Cambridge researchers, the key is the pygmies' life expectancy. "After going to the Philippines and interviewing the pygmies, I noticed this very distinctive feature of the population: very high mortality rates," says Andrea Migliano, a research fellow at Cambridge's Leverhulme Center for Human Evolutionary Studies and co-author of a new study published in Proceedings of the National Academy of Sciences USA. "Then, going back to life history theory, we noticed that their small body size was really linked to high mortality." Migliano and her colleagues began their study by comparing the growth rates of two Filipino pygmy groups (the Aeta and the Batak) with data from African pygmies as well as from East African pastoralist (livestock-raising) tribes like the Masai and the lower echelon of the U.S. growth distribution (in essence, malnourished Americans).All these groups have low nutritional status but reach significantly different average height levels. The U.S. population showed the greatest growth rate, whereas both the pygmies and African pastoralists lagged behind. Although the pygmies plateaued around 13 years of age, the pastoralists kept growing, reaching their cessation point into their early twenties.
View: Full Article | Source: Scientific American