For two years, British photographer Jimmy Nelson lugged his 4x5 plate field camera to 44 countries around the globe -- from the canopied rain forests of Papua New Guinea to the snowdrifts of northern Mongolia to the searing Namibian desert -- documenting a world fast disappearing. The goal of this visual anthropology, published in Nelson's new book, Before They Pass Away, was to capture the lives of remote and endangered tribes. "I wanted to witness their time-honored traditions, join in their rituals, and discover how the rest of the world is threatening to change their way of life forever," Nelson says. For politically correct Westerners, there could be something uncomfortably colonial about this sort of voyeuristic globe-trotting ethnography, yet Nelson's sensitivity for his subjects is immediately apparent. The tribes he captures might seem wild and somehow alien, but they show clear dominion over their remote and unforgiving environments, offering a remarkable glimpse back in time to how we urban dwellers once lived.