Small Body Size, High Mortality Rate, and Early Sexual Maturity in Pygmies

A new study suggests that high mortality rates in small-bodied people, commonly known as pygmies, may be part of the reason for their small stature. The study, by Dr. Jay Stock and Dr. Andrea Migliano, both of the University of Cambridge, may help unravel the mystery of how small-bodied people got that way. Adult males in small-bodied populations found in Africa, Asia, and Australia are less than four feet, 11 inches tall, which is about one foot shorter than the average adult male in the U.S. Why people in these populations are so small remains a mystery, but several hypotheses have been proposed. Some scientists think that small bodies provide an evolutionary advantage under certain circumstances. For example, a smaller body needs less food—a good thing in places where food supplies are inconsistent. Small bodies also may provide an advantage in getting around in thickly forested environments. Recently, however, a new hypothesis has come to the fore suggesting that reproductive consequences of high mortality rates may explain small body size. If death comes at an early age, then natural selection would favor those who are able to reproduce at an early age. But early sexual maturity comes with a cost. When the body matures early, it diverts resources to reproduction that otherwise would have gone to growth. So small body size could be essentially a side effect of early sexual maturity. Stock's and Migliano's study provides the first long-term evidence for the mortality hypothesis. The article appears in the October issue of Current Anthropology. [Press release] [Current Anthropology abstract]
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