Rationale for the Opinion that Humans Can Never Live Outside the Earth

There is controversy about whether humans can ever adapt to life outside the Earth. It is a realistic conclusion that the requirements for water, oxygen, and adaptation to zero gravity are major concerns. However, there is a notable insufficient emphasis on the cability of humans to adapt to new environments, which should override most hesitancy. There is one concern that should not be overridden: the continuous levels of space irradiation. Experiments with animal models, including those animals living in the Chernobyl postradiation environment and in controlled laboratory experiments, have indicated that multiple animal species, and likely humans, will be able to adapt to continuous levels of and increased baseline radiation exposure. However, we must understand the biology of human responses to radiation and relate the data to another concern, namely, the management of casualties from a nuclear reactor accident or the unthinkable consequences of exposure to radiation from fission or fusion bombs. Both space radiation and unplanned radiation exposure from an accident or weapon will require medical countermeasures. This is not simply an exercise in optimistic or pessimistic approaches to a controversy but rather addressing the reality of the biology of humans to adapt to a change in environmental levels of radiation.