Dual Phase Evolution Theory

Dual Phase Evolution (DPE, Dual phase evolution) is a theoretical framework proposed by David Green of Monash University, Australia, and others to explain the evolution of complex systems. This theory originates from observations of ecosystem evolution, including: 1) Punctuated equilibrium in species evolution shown by fossil records on geological time scales, meaning species numbers remain stable over a long period, followed by a mass extinction event and then a brief period of great explosion. 2) Quaternary palynology shows that vegetation can be divided into multiple periods by species composition; the species composition of vegetation differs greatly between periods, and transitions between them are often accompanied by fires. The main content of DEP theory is as follows (Green et al., 2006):

1) The state space includes two phases (phase): one phase (exploration phase) dominated by variation, and another phase (exploitation phase) dominated by selection.

2) With repeated transitions between the two phases, the complexity reached by the system gradually increases.

3) Transitions between the two phases are driven by external disturbances.

4) After disturbance, the system decouples into patches with low connectivity, at which point chaos can become a source of novelty.

5) As time passes, the connectivity of the system gradually increases.

6) When connectivity exceeds a threshold, unstable interactions and designs with poor fitness are eliminated by natural selection, leaving more complex, stable, and ordered structures. (Figures 3-5, 3-6).

DPE theory explains many complex phenomena, including continuous generation of novelty, modularity, scale-free networks, and criticality. DPE processes have been observed in large numbers of CAS at different scales: ecosystems, socio-economic systems, search algorithms, etc. The DPE process in ecosystems manifests as: when landscape connectivity is low, the selection pressure on species is smaller, so various variations are not immediately eliminated, increasing diversity. At this time, external disturbances only act on local patches without global impact. As connectivity increases, selection pressure increases, causing some species to go extinct and diversity to decrease, with the system entering a stable state. But the impact of disturbances (such as fires) also becomes global, ultimately dealing a devastating blow to the system and returning it to the phase of low connectivity. When the system is in the disconnected phase, it tends toward equilibrium, showing strong local variability but rarely large-scale variation. In the high-connectivity phase, local variability is small, but the response to external stimuli is unpredictable, showing obvious changes at all scales. Tight interaction networks, while providing stability mechanisms, also facilitate the spread of disturbances.

DPE theory has many similarities with SOC, but also some differences. SOC theory holds that complex adaptive systems self-organize to the critical state between order and chaos, while DPE theory holds that complex adaptive systems will cycle between two phases.