How to respond to change? Try to keep your inner state constant or instead adjust your inner state according to the external change?        

Staying constant inside is the classic idea of homeostasis, pioneered by the physiologist Claude Bernard in 1865 with the name coined by physiologist Walter Cannon in 1926. Homeostasis describes the essential feature of all living things that they define an inside and keep it stable in an unstable environment. Body temperature is a classic example.        

Homeostasis is, however, not very dynamic or darwinian: the business of living creatures is not to optimize their interior state. It is to survive. Whether or not the internal state is stable.        

Therefore, the concept of allostasis was created in the 1980ies by neuroscientist Peter Sterling and coworkers. The word allostasis means a changing state, where homeostasis means staying in about the same state. The idea of allostasis is that the organism will change its inner milieu to meet the challenge from the outside. Blood pressure is not constant, but will be higher if the organism has to be very active and lower if it does not have to.        

Constancy is not the ideal. The ideal is to have the relevant inner state for the particular outer state.        

The stress reaction is an example of allostasis: When there is a tiger in the room it is highly relevant to mobilize all the resources available. Blood pressure and many other parameters go up very quickly. All depots are emptied.        

The emergency stress reaction is a plus for survival, but only when there is a stressor to meet. If the reaction is permanent, it is not relevant, but dangerous.        

Allostasis also brings out another important physiological feature: looking ahead in time. Where homeostasis is about conserving a state and therefore looking back in time, allostasis looks forward. What will be the most relevant inner state in the next moment?        

The role of the brain is essential in allostasis because it predicts the environment and allows for adjustment, so that blood pressure or blood glucose level can become relevant to what is up.       

Although born in physiology, it is likely that the idea of allostasis in the coming years can become important as an umbrella for trends currently fermenting in the understanding of the mind.        

States of mind exemplify the role of relevance: It is not always relevant to be in a good mood. When the organism is challenged, negative emotions are highly relevant. But if there all the time, negative emotions become a problem. When there is no challenge it is more relevant to have positive emotions that will broaden your perspective and build new relationships, as described by psychologist Barbara Frederickson.        

Reward prediction has over the past decades become a key notion in understanding perception and behavior in both robots and biological creatures. Navigation is based on predictions and prediction errors rather than a full mapping of the entire environment. The world is described inside-out by throwing predictions at it and seeing how they work out. Controlled hallucinations has become a common phrase to describe this process of generously imagining or predicting a spectrum of perceptional sceneries—made subject to selection by experience. Very much like the scientific process of making hypotheses and testing them.

Prospection, originally described by Daniel Gilbert in 2005, allows a person to imagine several possible futures and observe the internal emotional reaction to them. Anticipating allostasis.       

Allostasis is an important concept for science because it roots the future-oriented aspects of the mind in bodily physiology.

It is an important concept in everyday life because it points to the importance of embracing change.