Since the late 1970s, cattle raiding with automatic weapons has escalated among nomadic herding societies in northern East Africa. We examine the impact of AK-47 raiding on the adaptability of Karimojong agropastoralists in northern Uganda. Most notably, raiding is linked to a loss of population resilience in Karamoja, measured in increased mortality of young children and of adult males in their prime reproductive years and decreased female fertility. AK-47 raiding has acted both directly and indirectly as a Darwinian stressor in this population, compromising long-standing adaptive strategies and intensifying selection pressure. We briefly discuss similar effects of recently altered patterns of raiding among related Turkana pastoralists in Kenya. We then consider the process by which this traditional cultural institution was modified in the interests of preserving cultural identity. We conclude nonetheless that cattle raiding with automatic weapons constitutes singularly maladaptive cultural behavior in contemporary pastoralist societies. Indeed, it represents the single greatest threat to their biobehavioral resilience and ultimately may have profound evolutionary costs in terms of pastoralists' survival. I. We are indebted to the Karimojong women who spoke with eloquence and honesty of the deaths of so many of their parents, husbands, siblings, and children during the terrible closing decades of the 20th century. Their stories were united by stark themes of violence that overshadowed all other considerations, compelling us SANDRA GRAY is

During the past four decades, biomedical scientists have slowly begun to recognize the unique opportunities for studying biomedical processes, disease etiology, and mechanisms of pathogenesis in populations with unusual genetic structures, physiological characteristics, focal endemic disease, or special circumstances. Such populations greatly extend our research capabilities and provide a natural laboratory for studying relationships among biobehavioral, genetic, and ecological processes that are involved in the development of disease. The models presented illustrate three different types of natural experiments: those occurring in traditionally living, modernizing, and modern populations. The examples are drawn from current research that involves population mechanisms of adaptation among East African Turkana pastoralists; a search for etiology and mechanisms of pathogenesis of an emerging disease among the Yakut people of Siberia; and psychosocial stress, hypertension, and cardiovascular disease in women working outside the home in New York City and among subpopulations in Hawaii. The models in general, and the examples in specific, represent natural laboratories in which relatively small intrapopulation differences and large interpopulation differences can be used to evaluate health and disease outcomes.

Tests of hand grip strength and hand grip muscle fatigue were conducted on Ngisonyoka Turkana pastoralists of northwest Kenya to explore some of the functional relationships between activity and body composition. The test of maximal voluntary contraction (MVC) of hand grip flexors was conducted on 151 Turkana and 38 U.S. men and women. The fatigue test was conducted on the same number of subjects who were instructed to attempt to maintain 80% of the MVC for 90 seconds. The results of these tests, combined with arm measurements of size and body composition, were used to evaluate muscle size and strength relationships and to estimate muscle fiber type distribution in the forearm. MVC values of Turkana men were low by U.S. and European standards. The low values resulted from smaller Turkana muscle areas. MVC values of Turkana women were comparable to those of U.S. and European women, reflecting comparable muscle areas. The fatigue curves of Turkana and U.S. men and women suggest that slow-twitch aerobic muscle fibers predominate for the hand grip flexors of the Turkana pastoralists.