We propose a hypothesis according to which there is a hierarchy of included steady states in living systems. Each steady state is not stable and exists only in a certain frame of time, named characteristic time. Evolution of system to any steady state leads to a change of boundary conditions for all steady states having lesser characteristic time. It should not be very rapid. In the opposite case, the level of entropy production could change so much that the system achieves a critical unstable point of any included steady state. Passing through the critical point leads to reorganization of the entire hierarchy of the steady states or to the complete collapse of the system as a dissipative structure. Also one should take into account that living systems are the result of long-term biological evolution. The species that are able to maintain their integrity for the longest time interval have evolutionary advantage. Therefore, it is quite likely that difference between current value of the entropy production and value of the entropy production in nearest steady state is small enough to satisfy the laws of linear thermodynamics. Experimental data confirm the hypothesis. Limits of applicability of linear thermodynamics to biological systems are discussed.