The Human Environment
As with any other species, human survival boils down to individual survival. This is true whether people die of disease, natural disaster, or manmade holocaust. Fundamentally, survival can be defined in terms of the interactions between an individual and its natural surroundings. The surroundings determine the extent to which a person is exposed to critical changes in environment, such as temperature, water, food, or oxygen. The physical world imposes strict limits on human biology, and learning where these limits are and how to deal with them is what biologists call limit physiology. The principles of limit physiology can be applied to understanding human life in all extreme environments. These principles will be developed in this chapter and applied throughout the book to gain a deeper appreciation of how humans survive in extreme conditions.
One of the most important characteristics of every living organism is its ability to maintain an active equilibrium, however brief or delicate, with its natural environment. All living beings, as integral parts of nature, can be characterized by the dynamic exchange they maintain with their physical surroundings. Being alive requires being attuned to natural change, and many organisms are exquisitely