Humans are found throughout the world, from the sub-zero temperatures of the Arctic to the humid jungles of the tropics. Such a widespread distribution is unusual in a single species and would usually be accompanied by a great deal of regional biological diversity to allow for adaptation to such disparate environments. However, humans are not very genetically diverse. It is likely that the complex behavioral and cultural adjustments that humans use in adapting to the environment have permitted their wide distribution without the need for major genetic differences. Still, humans do show some genetic diversity, and a portion of that variation is related to environmental conditions. To understand the way that humans have succeeded in colonizing most of the earth, we will need to consider both biology and culture.