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We analyzed data on Ju/'hoansi hunter-gatherer foraging patterns and found that their movements between residence camps can be modeled as a Lévy flight. The step lengths of their movements scale as a power law with an exponent μ=1.97. Their wait times (residence times) at the camps also scale as a power law (μ=1.45). A Lévy flight with step lengths μ=2 is an optimal search pattern for scarce, randomly located targets; thus, the Ju/'hoansi foraging pattern may approach an optimal search in this area of sparse plant and animal resources. These findings affect the application of optimal foraging theory to humans in anthropology and archaeology because they alter the way in which search and travel times should be quantified. These results may also carry implications for the study of other patterns of human movement, such as demic diffusion and migration.

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We have developed a method for studying the permeability properties of human endothelia in vitro. Human umbilical vein endothelial cells (HUVEC) were cultured on a substrate of human amnion. Confluent monolayers of these cells demonstrated 6-12 delta.cm2 of electrical resistance (a measure of their permeability to ions) and restricted the transendothelial passage of albumin from their apical to their basal surface. To determine whether leukocyte emigration alters endothelial permeability in this model, we examined the effects of migrating human polymorphonuclear leukocytes (PMN) on these two parameters. Few PMN migrated across the HUVEC monolayers in the absence of chemoattractants. In response to chemoattractants, PMN migration through HUVEC monolayers was virtually complete within 10 minutes and occurred at random locations throughout the monolayer. PMN migrated across the monolayer via the paracellular pathway. Although one PMN migrated across the monolayer for each HUVEC, PMN migration induced no change in electrical resistance or albumin permeability of these monolayers. At this PMN:HUVEC ratio, these permeability findings were correlated morphologically to measurements that HUVEC paracellular pathway size increases by less than 0.22% with PMN migration. This increase is insufficient to effect a measurable change in the electrical resistance of the endothelial cell monolayer. These findings demonstrate that increased permeability of cultured endothelial cell monolayers is not a necessary consequence of PMN emigration.