Evolution proceeds in phases, alternatingly convergent and divergent. During the divergent phases, many variants of an evolutionary system arise, and in the convergent phases, these are brought together in a new, higher unity, which in turn varies, and so on. Thus the mechanism of evolution is trialistic, proceeding according to the Hegelian principle (in the widest sense) of thesis, antithesis and synthesis. This mechanima is at the same time mirrored in the structure of the evolving systems, being most clearly expressed in the derivation of periodic systems of the individual levels of evolution. These relationships will be discussed using examples from symbiosis research, population dynamics and biogenesis.
1. PHASE PRINCIPLE
The evolution of ever more complex systems has not been a continuous process. Rather, it was driven by a constant alternation between divergent and convergent phases (Kuhn, 1976). According to this principle, each newly developed evolutionary system soon gives rise to many variants or mutations with similar chances for survival; for raw materials or sources of nutrition are present in excess. There are no major changes; this is a divergent phase. However, the explosive growth of the organisms gradually exhausts their resources. As soon as new variants appear which serve a new purpose, namely the utilization of new sources of energy or materials, a convergent phase is entered. The convergent phase is strongly selective, and the selection is directed. Only those representatives of the new variant survive which are best adapted to the new purpose. The transition from the divergent to the convergent phase is initiated by chance, but if the population is large enough and one waits long enough, this change must occur. It is not the event itself, but only the time at which it occurs which is a matter of chance. This effect is typical of evolving systems (Fig. 1).
It must be mentioned that not all scientists accept the above phase principle. To be ~sure, it is generally agreed that chance and necessity have than-