Evolution is a process of system's temporal gradual irreversible changes. Therefore, the evolution system is the system which changes gradually (permanently) and irreversibly.

The process of evolution can be either progressive (with rise in system's complexity and organization), or regressive (with reduction of system's complexity and organization). During evolution process important role belongs to both intrinsic factors and the environment of the system.

In concordance with the general systems theory by Y.A.Urmantsev only four basic non-evolutional transformations of a system (object-system) exist within the bounds of a system of objects of one and the same type (one type of systems which possess similar properties):
Identical - transformation into self;
Quantitative - transformation of "quantity" of primary elements;
Qualitative - transformation of "quality" of primary elements;
Relative - transformation of "relations" of primary elements
and 11 derivative transformations which are the combinations of the basic ones.

Evolutional transformations (which are given specific names) correspond to the above-listed non-evolutional transformations as follow:
Identical - stasigenesis;
Quantitative - quantigenesis;
Qualitative - qualigenesis;
Relative - isogenesis.

To undergo evolution the system must be of enough complexity to possess the potentiality of changing insignificantly, i.e. to hold fixed almost all the most insignificant divergences in structure, functions and behavior.
We are of the opinion that the most complete theory of non-evolutional and evolutional systems' changes is developed by Y. A. Urmantsev in his works "General Systems Theory" and Evolutionics.

Evolution allows to substantiate a great variety of objects of the Universe and their changes during existence, but it doesn't reveal the reasons of occurrence of fundamentally new instances and new classes of objects. Another type of irreversible processes (which are called revolution) allows to explain this phenomenon.

Revolution is an essential drastic qualitative change or a leap in gradual system's change, conjugated with gap between current and previous system's state (or gap between influence and its result).

Revolutionary processes are transient, so they can change systems considerably during rather a short period of time. It is precisely this fact that explains the occurrence of new instances and even new objects' classes.
However, revolution often causes disruption (decomposing) and elimination of systems. In this case the revolutionary process is defined as catastrophe.

The above mentioned definitions of irreversible systems' changes are phenomenological. They reflect the outer aspect of systems' changes only - systems' behavior perceived from without. Therefore this approach allows only to ascertain how irreversible systems' changes occur, but it does not allow to reveal the cause of irreversible changes and to understand the physics of inner processes.

Synergetics (the new science - a part of general systems theory) allows to understand and explain the inner physics of evolutional and revolutionary systems' changes.

Synergetics is a science about occurrence, maintaining of steadiness and disintegration of structures of different nature on basis of processes of self-organization in open non-linear environment.

The term "synergetics" was introduced by the founder of this science Hermann Haken in his work of the same name "Synergetics".

Synergetics revealed the systemic relation between macro-processes, which embrace the whole system, and micro-processes, which flow inside the system. This means that micro- and macro-processes, being independent, influence considerably on each other. Synergetics showed that in stable conditions of systems' existence macro-processes prevail, stabilizing the systems' behavior and determining evolutional changes. On then contrary, in the state of instability micro-processes prevail, they undergo considerable changes due to insignificant fluctuations, and this results in revolutionary change.

Thus, synergetics as a part of general systems theory allows to describe with an utmost precision the occurrence, existence and destruction of real systems of the Universe.