  The question "What is life?" has been asked and studied by the researchers of
various fields. Nevertheless, no global theory which unified various aspects of
life has been proposed so far. Considering that the physical principle for the
theory of birth should be the one known for the unanimated world, and that the
life processes are irreversibly selective, we showed by a deductive inference
that the maximum entropy production principle plays an essential role for the
birth and the evolution of life in a fertile environment. In order to explain
the survival strategy of life in a barren period of environment, we also
proposed that life had simultaneously developed a reversible on and off
switching mechanism of the chemical reactions by the dynamics of equilibrium
thermodynamics. Thus, the birth and evolution of life have been achieved by the
cooperation between the driving force due to the non-equilibrium thermodynamics
and the protective force due to the equilibrium thermodynamics in the
alternating environmental conditions.
