Underlying the theory of Spiral Dynamics is the core axiom that we adopt a system of values in order to survive in our environment. In other words, our circumstances lead us to value certain things that help us survive. If the world is full of primal danger, we form familial bands and stick together to avoid predators. If the world is full of violent anarchy, we come together to form government. If the world is a certain way, we adapt a certain way, and our values and consciousness shift accordingly.
Fundamentally, this process of value systems ("vMEMEs" as defined by the authors) engaging in a dance with environmental conditions ("Life Conditions") is a classic constraint satisfaction problem. Life Conditions are the constraint that our brains attempts to satisfy via vMEMEs. When a particular vMEME satisfies Life Conditions appropriately, it remains there until changing conditions necessitate a corresponding vMEME change.
As we can see through the many stages present in the spiral, there have been many attempts at solving the problem of surviving in the environment. The "First Tier" vMEMEs reflect successive attempts that each worked for a time, but eventually faced categorically new conditions it was not equipped to handle, fostering change to a new way of thinking - a new vMEME.
The "Second Tier" vMEMEs, however, are fundamentally different. At Stage Yellow, the first integrated, multiperspectival approach is achieved, which incorporates all stages below it. While first tier vMEMEs were local solutions for specific constraints, Yellow represents the first 'general solution' that applies not to specific constraints, but to constraints in general. However, as we see a shift to Turquoise, it does not see the whole picture yet.
Turquoise, in its full form, sees the whole picture. As a Turquoise-level theory, Integral Theory by Ken Wilber maps out the categorical structure of all of reality. Thus, all Life Conditions can be mapped by this theory, since any Life Condition is just a particular moment in reality. Turquoise includes this holistic, comprehensive view of reality in its value system, and adapts itself accordingly. This last point is extremely significant, and worth reiterating - Turquoise is adapted to the very structure of reality itself. Thus, any Life Condition that may arise is compatible with the Turquoise value system. Since no further advance is necessary, ever again, Turquoise is the last stage in the theory of Spiral Dynamics.